Distribution considerations

Distribution is the way a media product is shared, spread out or released so that an audience can actually get to it. A finished product that nobody receives has not really been distributed, so the route you choose affects who can access it and how quickly they receive it.

Online distribution

Online distribution sends the product over the internet. It covers the World Wide Web, meaning pages viewed in a browser, and other internet services such as streaming, which delivers audio and video as it plays. Nothing physical changes hands: the audience streams or downloads the file onto a device they already own, so the product can be with them in seconds.

Online distribution is used for:

• video, music and podcasts, such as a youth theatre group making a filmed version of its pantomime available to download from its website
• image sharing and social media, such as a school art department hosting a gallery of students' ceramic work on the school website
• digital publishing, such as news and reviews: a school science department puts its revision newsletter on the school website as a PDF

Physical distribution

Physical distribution puts the product onto a tangible item the audience can hold, such as paper, a disc or a memory stick. That item is printed or copied, packaged and then handed over, posted or sold, so the audience must have the item in front of them before they can use the product.

For example, a model railway club prints a track-plan booklet to sell at its open day, while a downloadable copy sits on the members' webpage for people who have moved away. One product, two routes: the club reaches visitors who want a printed keepsake at the event and former members who want it straight away.

A streaming service uses the internet to deliver audio and video that plays as it arrives, rather than handing the audience a file to keep. The programme or track is only part of what reaches them.

Is it web distribution?

Streaming counts as web distribution only when the audience gets it through a browser. Someone who opens the service's site on a laptop or tablet is using the web. The same service reached by tapping an installed icon on a phone or a smart TV is distribution through an app instead. An app and a website are separate routes, so say which one the audience actually uses.

For example, an online observatory called Starline streams live telescope views. Watching it in a browser window on a laptop is web distribution; opening the Starline app on a phone is not.

What else gets distributed

Alongside the main programme, a service also distributes supporting content:

• Title images – thumbnails that catch your eye and show what each episode or track looks like.
• Text descriptions – short summaries and episode notes that help you choose something and understand it once it starts.
• Interface graphics – buttons, menus and icons you use to search, play and pause.
• Subtitles – on-screen text of the speech, which helps in a noisy room and for viewers who are deaf or hard of hearing.

These assets are part of the distribution, not decoration: the audience relies on them to pick what to watch or listen to and to follow it afterwards.

So a streaming service distributes the programme or track together with the supporting content that surrounds it.

Online distribution means releasing a product over the internet, through a website, an app or a streaming service, rather than on a physical item. It has real strengths, but also limits worth weighing against physical media.

Why providers choose online distribution

The audience gets instant access: a new episode of a school-run podcast plays the moment it is published, with no delivery wait. There are no geographical limits, so a small animation studio in Leeds can reach viewers in Brazil or Japan. Providers have lower costs because nothing is manufactured, packaged or shipped: no cases, no printing, no courier. The audience needs no physical storage space for shelves of discs. Online distribution can also be greener, cutting down on discarded plastic and on the emissions created by making and delivering discs.

Providers can collect analytics: which trailer was watched to the end, where viewers paused or left, and how often they returned. That helps them improve what they make. Providers can also scale up to a very large audience without making extra physical copies.

What can go wrong

A stable internet connection is needed and is not available everywhere, such as on a train through the countryside. High-quality streaming uses a lot of bandwidth, which is a problem on a limited mobile data plan. Access usually depends on a subscription or account, and the provider can remove a title or shut the service down, so you may lose access and do not own the copy as you would a disc. Geoblocking blocks some content in certain regions because of licensing agreements. Unauthorised copying and sharing are simpler with digital files than with physical copies.

Playback may stall while it loads (buffering), and outages can interrupt access. And having several services can leave consumers overwhelmed by too much choice and too many monthly fees.

A platform is a combination of computer hardware and an operating system. The hardware is the physical device, and the operating system is the software that runs and manages it. Because platforms run different operating systems, the software available differs between them, so a product built for one platform may not run on another.

Platforms come in two groups. The physical platforms are computers, interactive television, kiosks and mobile devices; online platforms include apps, websites and other multimedia services. Whatever the group, a platform delivers the product to the audience by running it and presenting it.

Media are the items that carry the product, and a single item is a medium. Paper, a disc and a memory stick are media. A smartphone is a platform because it runs the product, while an SD card is media because it stores and carries it. A website is an online platform, but a printed booklet is paper-based media.

Keeping the two apart

Platform and media must not be confused. When naming a platform, give the device or system that runs and presents the product; when naming media, give the tangible item that holds it. A garden centre, for example, could show a plant-care guide on a tablet: the tablet is the platform, and a printed care card is media.

Platforms and media compared

A computer is a physical platform for distributing a media product. It includes desktop machines, which stay in one place, and laptops, which fold shut and can be carried.

Computers are flexible because you can install a wide range of software and apps on them. A user could install an animation tool, open a browser, run a game or view an interactive product. That means one computer can present many different media products, and the audience is not limited to a single built-in service.

Computers usually have a web browser. This lets the audience use websites, such as watching a video on a web page or browsing a web-based gallery. For distribution, that is useful: a product placed online can be opened on a computer without a separate app being installed.

Portability

The main limitation is portability. A desktop is not portable at all, and a laptop is portable but much less easy to carry in a pocket than a phone or tablet. So a computer suits an audience sitting at a desk or on a sofa with a laptop, but it is awkward for someone who needs the product while travelling.

Controls

Computers are usually controlled with a mouse, keyboard or touchscreen. This is precise for typing, selecting small details and design work. However, it is less convenient than a television remote control when the audience is sitting back to watch. For example, a school could put a virtual art exhibition on its website; computers can open it and show detailed artwork, but a visitor on a bus would need a more portable platform.

Mobile devices are portable computers such as smartphones and tablets. You carry them with you, and they run feature-rich operating systems that support many apps, a web browser and multimedia playback.

That makes them useful for reaching an audience on the move. For example, a city library could release a short animation about its reading challenge through a phone app and a mobile web page, so visitors can watch it on a bus or while waiting in a queue. An app is installed on the device, while a mobile web page is opened in the device's browser. A tablet is small enough to pass around, which suits a family watching together or a group on a journey.

Design limits

Mobile devices have small screens, so content must be designed for a small display. Use readable text sizes, simple layouts and large, easy-to-tap buttons. A product built for a wide desktop screen may need a mobile version with fewer columns and shorter lines.

Streaming over mobile data can also be expensive, particularly high-quality video, because it uses up a data allowance. A lower-bandwidth option, such as a smaller video or an audio version, helps the audience use the product without worrying about cost. On Wi-Fi the same video usually costs nothing extra, so the expense depends on how the audience connects.

When you choose mobile devices as the platform for a product, they give reach and convenience, but the product must be adapted to the small screen and to data limits.

An interactive television, often called a smart TV, is a television that receives broadcast digital television and also connects to the internet to use streaming services. It is interactive because you choose what to watch and when, rather than only watching what is being broadcast. It can also show apps, your own photos and music on the screen and speakers.

Its strengths come from where it sits: in the living room. A remote control lets you choose a programme from the sofa without a keyboard or mouse, which suits family viewing. The large screen makes high-definition films and television more enjoyable, and it is comfortable for several people to watch together. Television makers test the hardware and software so that streaming services and apps play reliably, which gives the audience a smooth experience rather than a stuttering one.

The main weakness is the limited range of apps and services. A smart TV offers fewer apps and services than a computer or mobile device, so a product that depends on a niche app may not be available on it. A service can also be missing if the television's software is older or the maker has not added it.

Choose a smart TV when the audience wants comfortable, large-screen streaming in a shared room, but check that the required service is supported. For example, a tennis club wants to show match highlights at a social evening. The clubhouse smart TV gives a big picture and a simple remote control, but the club must first check that the highlights are on a service the television can open.

A kiosk is a computer built into a stand, often in a public place. It has a touch screen and limited functionality: it usually delivers images, animation and sounds, not a full desktop where users can install or open anything they like.

Types of kiosk

• Self-service checkouts let customers pay for their own items without a cashier.
• Information kiosks show maps, photos and text, such as a zoo screen giving enclosure locations and feeding times.
• Internet kiosks let the public open websites, such as a leisure centre screen for opening a swimming club's website.
• Advertisement displays loop animations and short video, such as trailers in a cinema foyer.
• Service kiosks let people complete a task themselves, such as requesting a replacement bin at a town hall.
• Ordering kiosks let customers choose items, such as a bakery screen for ordering a birthday cake.

Why kiosks suit public places

A kiosk can be locked to a single service, so the public cannot close it, load other services or delete the app. A zoo can leave its map running all day, and it should still work properly the next morning.

A kiosk can be updated digitally and automatically. New images and text can be sent to every unit at once, so staff do not visit each machine and the venue saves the cost of printing and reprinting paper guides.

Drawbacks

Being locked down is also a limitation. A visitor cannot use a zoo-map kiosk to check train times, and adding an extra service may not be possible. The hardware can fail too: an older kiosk with a slow processor and a low-resolution screen may not run a new high-definition animation, and a unit without a card reader cannot take payments.

Paper-based media are the printed group of physical media; the other two groups are removable flash memory and discs. Paper carries images, illustrations, photos and text, so it suits a product the audience reads, keeps or displays rather than plays.

What counts as paper-based media

The media are the items themselves: printed publications such as magazines, newspapers and books, plus flyers, maps and posters, including billboard posters. Name the item — a leaflet, a trail map, a poster — because the medium is the physical thing that carries the product, not the event it advertises.

For example, a city farm prints a folded trail map for visitors and a printed activity booklet for school groups. Both are paper-based media; neither needs a screen.

Why print costs what it does

Full-colour printing costs more than mono printing, which uses a single ink, because full colour lays down four inks: cyan, magenta, yellow and key (black). Each ink means more plates, more passes through the press and more setting up, so a full-colour poster costs more per copy than a black-only price list.

Distribution adds a second cost. Printed items are run off, packed, then moved physically through the supply chain. For example, a print shop runs off 500 programmes for a school show; some are boxed and couriered to the school office, and the rest are posted to relatives who live too far away to come. Delivering the same item online avoids that journey, which is why paper is much more expensive to distribute.

What paper does better

• It can reach every household by post or a door drop, with nothing to sign up for.
• It needs no account, device, electricity or batteries, so a reader can use it anywhere.
• It shows up well in bright sunlight, unlike a phone screen.
• It cannot be corrupted or fail like a device, though it can of course be torn or soaked.

An optical disc is a physical medium that carries a media product such as music or a film, and it plays in a matching player. The CD, DVD and Blu-ray are the main types. All three are 12 cm across, so their capacity, not their physical size, is the best clue to what each one suits.

A CD holds about 650 to 700 MB. That is enough for roughly 74 to 80 minutes of uncompressed audio, about the length of a music album, so a band can fit its whole album on one disc. Uncompressed audio takes a lot of space because none of the sound data is thrown away to shrink the file.

A DVD stores standard-definition video. A single-layer DVD holds about 4.7 GB and a dual-layer disc about 8.5 GB, so a longer film or extra features have more room. A double-sided, dual-layer DVD holds about 17 GB by using both faces and two layers, but the disc may need turning over part-way through and has no room for printed graphics, because both sides carry data.

A Blu-ray disc holds around 25 GB on one layer and up to 50 GB on two. High-definition video needs much more data for every second of picture than standard definition does, so the larger capacity lets one disc carry a full HD film at high quality.

Suppose a community garden group films a standard-definition guide to its allotments and the footage comes to 6 GB. A single-layer DVD holds 4.7 GB, so it is too small; a dual-layer DVD holds 8.5 GB and fits. A Blu-ray would fit too, but the group's laptop and the village hall both play DVDs, so the DVD is the sensible choice.

Removable flash memory is portable storage that you can take out of one device and plug into another. The main forms are memory sticks (USB flash drives), SD cards and the smaller mini or micro-SD cards. It is physical media: the card or stick is the item that carries the files, so it is not a platform.

These cards and sticks are sold in many capacities, with 1 TB or more available. That is enough to carry a large collection of photos, audio or video. They are often used to store and share media files, such as photos taken on a camera, a portfolio of artwork to take to an interview or a video clip for a presentation. You copy files onto the card using a computer, then move it to another device or hand it to someone else.

Sharing without an internet connection

Removable flash memory is especially important when files have to be shared where there is no internet connection. For example, a geography field trip group could fill an SD card with photos and short videos on a camcorder, then take the card to a laptop back at school to review and edit them. No upload, download or account is needed. It also helps you give files to someone who is offline: you can pass them the stick or card directly.

Practical points

Its main practical advantage is that it is small and portable, and it does not need an internet connection to transfer files. A memory stick can fit in a pocket, and a micro-SD card is very small. The card or stick still needs a compatible slot or reader in the device, and it can be lost or damaged, so keep a backup. Even so, it is a simple physical way to move large media files between devices.

Physical media are tangible items that carry a media product, such as a CD, DVD, memory stick or printed pack. They are a distribution option alongside online delivery, and they have strengths and weaknesses you can weigh up.

Advantages of physical media

Tangible ownership means the audience has something they can hold. That makes physical media good for building and displaying a collection, such as a set of illustrated recipe cards or a shelf of album CDs. A disc or printed pack also makes a ready-made gift, because it can be wrapped and given without needing an account or a download code.

No internet connection is needed. A printed revision booklet can be read on a coach with no Wi-Fi, and an audio CD of a school concert will play on a kitchen stereo that has never been connected to the internet. The copy is also owned outright: buying a DVD means you can keep watching it even if a subscription service later drops that film or changes its licensing deal.

Disadvantages of physical media

Physical media take up storage space. Boxes of CDs, DVD cases and printed packs need shelves, cupboards or a bag, which matters when space is limited.

They cost more to produce and move. Manufacturing, packaging and shipping add expense: discs must be pressed, cases and sleeves printed, and stock transported to shops or customers. There is an environmental impact too, from plastic cases and wrap creating waste to the carbon emissions of delivery vans and lorries.

Stock can run out. A popular title may be out of stock, so the audience waits for a delivery or makes a trip to a shop. Finally, physical items can be damaged: a memory stick dropped in a puddle may lose a media project completely, and a printed pack left in a damp cupboard can warp until it cannot be read.

Choosing a platform or a medium is a decision about how a product reaches its audience. It depends on the audience, where and how the product will be used, portability, screen size, internet availability, cost, capacity and the quality needed. A product for people on the move needs a portable platform; high-definition video needs a medium with room to hold it.

Choosing the medium

Capacity and quality drive the choice: a CD holds about 700 MB, enough for an album, while high-definition video needs the space of a Blu-ray. DVDs and Blu-rays are the same physical size; the difference is how much they hold and the video quality they can carry.

How the platform shapes the file format

The device and its operating system must be able to open and play the file, so the platform's characteristics decide the format. Storage matters: a phone with little space free cannot hold a long, high-quality video. Screen size and resolution matter: a large television can show fine detail that a small phone screen cannot, so it needs the sharper version. The internet connection matters too: a slow or capped connection needs a smaller file that will not stall or swallow a data allowance.

A bike-repair charity films short how-to videos. Most of its viewers use older phones on limited data, so it exports smaller, lower-resolution files that play smoothly; for volunteers with no internet it puts the full-quality files on a memory stick.

Checking compatibility

Compatibility is checked before distribution by trying the finished file on the target platform to be sure it opens and plays. A file in a format the platform cannot open will never reach the audience, however good it is, so platform, medium and format must fit together.

A file format is the way data is stored inside a file. Two files might hold the same song or picture but arrange the data completely differently, and each arrangement is a different format. The file extension is the short tag at the end of a file name, after the full stop, which shows which format that file uses.

Extensions exist so software can recognise a file without having to guess. When you double-click match_highlights.mp4 your computer reads mp4 and hands the file to a video player; open shopping_list.txt instead and a text editor launches. The extension is only a label that points to the format — it does not hold the content itself.

Reading an extension

Extensions are usually three or four letters, often lower case: .png, .mp3, .docx. A file name can contain more than one full stop, so software always looks at the part after the last one. In trip.2025.jpg the format is jpg, and the earlier full stop is just part of the name. Some formats also use a longer version, such as .jpeg or .mpeg, which the same software still recognises.

When the label is wrong

Renaming a file does not convert it. Change cookbook.docx to cookbook.pdf and the computer will happily try to open it as a PDF, but the data inside is still in DOCX, so the file either refuses to open or appears scrambled. That is why the extension must always match the format the file was actually saved in — a correct match is what gets the right software to open it.

filename = "book_report.docx"
extension = filename.rsplit(".", 1)[1]

opening_software = {"docx": "word processor", "png": "image viewer", "mp3": "music player"}
print("Extension:", extension)
print("Open with:", opening_software.get(extension, "app not found"))

Output:

Extension: docx
Open with: word processor

Raster (bitmap) images, such as photographs, are made from a grid of tiny squares called pixels. Pixel dimensions are the number of pixels across the width and the number down the height of an image, written as width × height.

A photo of a school football team saved at 2400 × 1600 contains 3,840,000 pixels. Crop the same photo to 240 × 160 and it contains 38,400 pixels — one hundredth of the pixels.

More pixels allow an image to hold finer detail. Thin lines stay crisp, curved edges look smooth and small text remains readable. If you show two versions of a picture at the same size on a screen or on paper, the one with higher pixel dimensions packs more pixels into the same space, so each pixel is smaller and the picture looks sharper.

With too few pixels, the image has to be enlarged to fill the space. Each pixel becomes a visible block and the edges look jagged or blocky, which is called pixelated. For a given use — such as a large printed photo or a small on-screen picture — higher pixel dimensions generally give higher image quality, provided the extra pixels are actually needed at that size.

A huge pixel count mainly helps when the picture will be viewed large or zoomed in. A tiny thumbnail does not reveal the benefit of millions of extra pixels. Pixel dimensions also do not guarantee a good picture on their own: a blurry or badly lit photo stays blurry even at a high pixel count.

DPI (dots per inch) and PPI (pixels per inch) both measure resolution: how many dots or pixels are packed into one inch of an image. A higher number means more detail in each inch, so the image looks sharper.

Print and screen

DPI is used for print resolution. It counts the dots of ink a printer places in one inch of paper. PPI is used for screen resolution. It counts the pixels shown in one inch of a display. People sometimes say DPI when they mean PPI on a screen, but the correct term there is PPI.

Quality

A higher resolution gives more detail and higher image quality. At a lower resolution, there are fewer dots or pixels in each inch, so edges and fine detail can look blurred or pixelated. For example, a printed photo at 600 DPI can show the fine fur on a pet, while the same photo at 60 DPI may look soft and blocky.

Resolution and pixel dimensions

Pixel dimensions are the number of pixels across and down an image, such as 2400 wide by 1600 high. Resolution is a separate property: the same 2400 by 1600 image can be set to 250 PPI or 500 PPI. At 250 PPI it is displayed or printed larger, with fewer pixels in each inch; at 500 PPI it is smaller, with more pixels in each inch, so detail looks finer. Changing the PPI setting does not add pixels — it changes how tightly they are packed.

Digital images are stored in one of two ways: as a raster (also called bitmap) image or as a vector image. The difference becomes obvious when you make an image bigger.

Raster images

A raster image is made from a grid of pixels — tiny squares, each holding one colour. The image is just that grid, so its quality depends on how many pixels are in it. If you zoom in far enough, you see the individual squares. If you enlarge the image, the software stretches the pixels it already has and guesses the gaps, so edges turn jagged and blocky. This is pixelation.

For example, a photo of a school netball team taken at a small size looks fine on a phone. Blown up to cover a sports hall banner, the players' faces become a patchwork of coloured squares. Raster images suit photographs, where every pixel may be a slightly different shade.

Vector images

A vector image is not a grid of pixels. It is made from lines, curves and fills, stored as instructions: draw a curve from here to there, fill this shape with blue. When the image is enlarged, the instructions are used to redraw it at the new size, so the edges stay crisp. A vector logo on a small membership card can be scaled up for a large shop sign with no loss of quality.

Vector images suit logos, icons and diagrams built from clean shapes. A vector image is not automatically better quality — a simple drawing is still simple — but scaling it does not cause pixelation.

Comparing raster and vector

Raster image formats include JPEG, PNG, GIF, TIFF and RAW. Each format balances file size, quality and features, so the right choice depends on how the image will be used.

JPEG uses lossy compression and gives small files, which is useful for a sports-day photo you attach to an email. It does not support transparency. PNG uses lossless compression and supports transparency, so a cut-out photo of a badminton shuttlecock can sit over a poster for the school club without a pale rectangle behind it.

TIFF is uncompressed and keeps all the image data, making it suitable for high-quality printing, such as a scanned pressed-leaf collection where the faint veins must be kept before it is printed for a nature display. RAW is also uncompressed and is used by professional cameras; files are large, but they are good for editing, letting a photographer brighten a dark photo of an owl. GIF is heavily compressed and can hold multiple frames for simple animation, like a looping arrow on a classroom slide. It is now largely obsolete except for those simple animations.

Vector image formats store artwork as shapes, lines and curves, so the picture can be made larger or smaller without turning blocky. Two common vector image formats are SVG and EPS.

SVG and EPS

SVG is designed for screens and the web. Because it describes shapes rather than pixels, an SVG file is usually small, and it can be scaled to fit a phone or a large display without loss of quality. SVG can also include animation, such as a shape that moves or changes colour. For example, a museum's online floor plan could use SVG, with a small dot that pulses to show where you are. EPS is another vector format, often used for artwork that will be printed, because a printer can scale it cleanly.

SWF and older animations

SWF is a vector animation format, but it needs a plugin to play. Modern browsers no longer support the plugin, so SWF is now uncommon and a poor choice for a new product. An old revision game with a bouncing character saved as SWF may not open on a current laptop.

Storing animation

Animation can be stored in video formats such as MP4, or in vector formats such as SVG. MP4 works well for detailed or photographic animation that needs to play in many places. SVG suits simple animation made from shapes, such as a recipe app where a whisk icon rotates while a timer counts down. The choice depends on the content and where it will be used: MP4 for realistic motion and wide playback, SVG for small, sharp, shape-based animation.

Sound in the real world is analogue: it travels as a smoothly changing wave. Computers store and process numbers, so analogue audio must be digitised before it can be saved or edited. Digitising means taking measurements of the wave at regular moments in time and storing each measurement as a number.

Sample rate

Sample rate is the number of times sound is sampled each second, measured in hertz (Hz). A sample rate of 48,000 Hz means 48,000 measurements are taken every second. A higher sample rate takes more measurements per second, so the digitised version follows the shape of the original wave more closely. This makes the sound more accurate and improves quality. Imagine recording a friend's drum kit: at a low sample rate, a very quick cymbal hit might fall between samples and be missed. At a higher sample rate, there are more chances to capture it.

Bit depth

Bit depth sets how many bits are kept for every single sample. This decides how many possible levels each sample can be stored at, so it determines the accuracy of each measurement. With 8-bit depth there are 256 levels; with 12-bit depth there are 4,096 levels. More levels mean each sample can be stored closer to its true height, which gives better sound quality, especially for quiet details.

Sample rate and bit depth are different properties: sample rate is how often you measure the wave, while bit depth is how precisely each measurement is recorded.

Audio file formats are the different ways digital sound is saved, such as WAV, MP3, AAC, FLAC and Ogg. The format you choose changes two things: how much of the original sound is kept, and how much storage the file needs.

Formats that keep all the sound

WAV is normally uncompressed. It stores every sample exactly as it was recorded, so it gives the highest quality, but the files are very large. A three-minute WAV of the school orchestra rehearsal takes up more than 30 MB, so a whole concert would use a big slice of a phone's storage, and the file takes a long time to send over the internet.

FLAC is lossless compressed: it packs the same sound into a smaller file without throwing anything away, so the quality matches WAV. FLAC is open source, so it does not require licence fees and app developers can add support without paying. However, not all players support it, so a FLAC track you send to a friend might not open on their device.

Lossy formats

MP3 is lossy compressed: it permanently removes the parts of the sound people are least likely to notice. The file becomes small and nearly every device will play it, but some quality is lost.

AAC is a lossy compressed format, and at the same file size it gives better sound quality than MP3. The drawback is that not all players support it, so check compatibility before you distribute a file.

Ogg is a lossy compressed format too, so files stay small, but fewer devices and programs can play it than MP3.

Frame rate describes how many individual still images are displayed in each second of a moving image. Each frame is a single still picture, and playing many of them quickly one after another creates the illusion of movement. Frame rate is measured in frames per second (fps).

What the numbers mean

A clip at 30 fps shows 30 separate pictures every second. Raise it to 60 fps and you show 60, so each second is split into twice as many moments. Because every frame stays on screen for less time, a moving subject is caught in smaller steps from one frame to the next.

For example, a pupil waving at the camera at 15 fps might see their hand jump to a new position between frames, so the wave looks jerky. Film the same wave at 60 fps and the gaps between positions are tiny, so the hand moves smoothly.

Smoother motion

Higher frame rates produce smoother motion. The extra frames fill in the movement, so your eye sees a continuous flow rather than a series of separate pictures. A low frame rate can make quick movement look jerky, and a fast object may seem to jump from place to place rather than glide across the screen.

Fast movement needs more frames

When things move quickly, a fast frame rate matters more. A clip of a bee darting between foxgloves, a dog shaking water from its coat or a chef tossing a pancake in a pan all change position a lot from moment to moment. Plenty of frames each second keeps that action smooth instead of choppy, and helps you spot the detail of what happened. Fast frame rates are important for fast-moving content, because there is more change to capture between frames.

Frame rate is not the same as resolution. Resolution is about the number of pixels in each frame, while frame rate describes how many frames you see every second.

Resolution describes how much detail a video frame can hold, based on the number of pixels across and down. Comparing frames by their resolution standards helps you judge and compare video quality.

SD, HD and UHD

SD (standard definition) is a lower resolution video format, so the picture can look softer and less detailed. HD (high definition) has a higher resolution than SD and comes in more than one level, such as 720p and 1080p; the number is close to the number of pixel rows down the frame. A higher HD level has more pixels than a lower one, so it can show finer detail.

UHD (ultra high definition) is a higher resolution than HD, and the UHD family is split into two tiers, 4K and 8K.

Why it matters

Higher video resolution significantly improves picture quality because more pixels can show finer detail, cleaner edges and more realistic textures. For example, a clip of a busy market filmed in SD can look blocky on a large screen, in HD the signs on each stall are easy to read, and in 4K you can pick out individual price tags.

A video file format is the way the frames and sound of a moving image are stored in a file. Formats store or compress video in different ways, which affects file size, quality and whether a device can play the video.

Common video formats and compression standards include MP4, AVI, MOV, WMV, MPEG-2 and H.264.

MPEG-2 is an older compressed standard still used for some broadcast and disc video. H.264 is a compression method often used inside MP4 files.

Compressed or uncompressed?

Uncompressed video preserves all the original data and gives the highest quality, but the files are very large. A short clip can take up more storage than a whole folder of photos. Compressed video reduces the file size by storing less data. The more compression applied, the more likely you are to see digital artefacts — blocky, smeared or fuzzy patches, especially around fast movement or sharp edges.

For example, a youth theatre group recording its summer show might export an MP4 for its website so parents can watch on a phone without a long wait. It keeps an uncompressed copy until the final edit is agreed, so every cut is made from complete data.

Compatibility matters

A format is only useful if the audience's device can open it. Less common formats may have compatibility issues: a video saved in a rare format might not play on a phone, tablet or smart TV, so the audience sees nothing at all. Checking support before distributing a video avoids this problem.

Compression is the process of reducing the size of a file by reducing the amount of data it contains. A compressed song, poster or game level still plays, opens or works, but it takes up less room.

Why compress a file?

Every file you store or send costs space and time, and compression cuts both:

• Storage — a phone, memory card or school network drive holds far more files when each one is smaller, so you run out of room less often.
• Transfer — a smaller file uploads, downloads and streams more quickly, because there is less data to push across the connection.
• Web pages and online media — a photo-heavy page opens sooner on a weak mobile signal, a video streams with less buffering, and a podcast episode downloads faster before a journey.

What it can cost

The two main types are lossy compression and lossless compression. Lossy compression discards some of the original data, so the file can lose quality — though often you would not notice unless it is squeezed very hard. Lossless compression throws nothing away, so the original quality is kept. Which one suits a file depends on whether its exact contents must survive.

A worked example: a 300 MB project file takes 60 seconds to upload over a connection that carries 5 MB every second. Compressed to 60 MB, the same upload takes 12 seconds. The time saved by sending less data is often worth more than the space saved on the drive.

Lossy compression reduces a file's size by removing or discarding some of the original data. The file still opens, plays or displays, but it no longer holds everything the original did, so some quality is lost — and that removed data can never be put back.

How much is thrown away?

Lossy compression usually gives a significant reduction in file size. You often choose the compression level yourself, and the more heavily a file is compressed, the more information is lost.

• Light compression keeps most of the detail, so the result usually looks or sounds the same as the original.
• Heavy compression discards much more, and the drop in quality becomes easy to spot.

Imagine a school orchestra recording a rehearsal on a phone to send to a group chat. At a light setting the strings and voices sound as they did; squeeze the same recording much harder and the cymbals smear and quiet passages go fuzzy. That copy is fine for a quick message, but not for selling the concert CD.

Digital artefacts

Heavy compression can cause digital artefacts: visible or audible damage that was not in the original. A picture may show pixelation, where smooth areas break into blocks and edges look jagged; audio can turn watery or metallic. At moderate settings the loss is normally hard to notice, which is why the method is so widely used.

When to use it

Lossy compression suits any situation where a smaller file size matters more than keeping every piece of original data or perfect quality, such as shrinking a photo before you send it so it uploads quickly over a weak connection. It is the wrong choice when the file must stay identical, like a spreadsheet of race times where every hundredth of a second counts. It removes detail inside a file; it never removes whole files or whole sections.

Lossless compression makes a file smaller without throwing away any of the original data. Every detail that was in the file is still there afterwards, so the quality stays exactly as it was.

When every detail has to stay

Lossless compression is used when the contents of a file must stay exactly the same and any loss of data would be unacceptable. Imagine a vet takes an X-ray of a dog's leg and stores it in the practice's records. The image must stay exactly as it was so a tiny hairline fracture is still visible when another vet checks it weeks later. Compressing the X-ray losslessly means it takes up less storage space and is quicker to send, yet none of the original image data has been lost.

Smaller savings, nothing lost

Lossless compression usually gives a smaller reduction in file size than lossy compression. The file does get smaller, just not by as much, because no data has been removed to free up space.

For example, a 40 MB X-ray might shrink to about 16 MB with lossless compression. Lossy compression could take the same X-ray down to 3 MB, but only by removing some of the detail, and a fine hairline fracture could end up blurred. So lossless is the right choice whenever keeping every piece of the original data matters more than making the file as small as possible.

Decompression is the process of restoring a compressed file so it can be opened, read, played or used. When you download a compressed file, the software you use usually decompresses it first, because most apps can only work with a file once its data is back in its usual format. The decompressed file also takes up more storage space again.

The result depends on how the file was compressed. With lossless decompression, the decompression algorithm rebuilds every piece of the original data, so the decompressed file is exactly the same as the file before compression. For example, a scanned copy of a signed trip consent form might be compressed losslessly to save space when emailed; when the school office decompresses it, every letter and signature is identical to the original scan.

With lossy decompression, the file is rebuilt so it can be used, but the data removed during compression cannot be put back. The decompressed file is not exactly the original. A recording of a school choir rehearsal compressed lossily for a highlights video will still play after decompression, but the quietest details that were discarded are gone for good.

Compression and decompression are different

Compression reduces file size. Decompression restores a compressed file for use. They are opposite processes, not the same one.

Both lossy and lossless compression make a file smaller. The important difference is what happens to the original data and to the quality.

Lossy compression

Lossy compression makes a file smaller by discarding some of the data or detail. This can lose quality, especially if the file is compressed heavily, but it usually gives the largest reduction in file size: a 24 MB file might become 6 MB. Choose lossy compression when a much smaller file matters more than keeping every piece of original data or perfect quality. It does not delete whole files; it reduces the amount of detail stored inside the file.

Lossless compression

Lossless compression reduces file size without removing any data. Nothing is discarded, so the contents stay exactly the same and the original quality is kept. It usually gives a smaller reduction in file size: the same 24 MB file might become 18 MB. Choose lossless compression when the contents must stay exactly the same and any loss of data is unacceptable.

Comparing the two