Moving Image Files
Properties of Digital Moving Image Files
Frame Rate
A moving image is not truly continuous motion — it is a rapid sequence of individual still images called frames. Frame rate is the number of those frames displayed every second, measured in fps (frames per second). The faster the frames change, the more convincingly the brain perceives smooth, continuous movement.
A low frame rate — say, 12 fps — produces noticeably jerky or stuttery motion. A frame rate of 24 fps is the long-established standard for cinema, creating the particular look audiences associate with film. 25 fps is standard for broadcast television in the UK (matching the 50 Hz electrical frequency). 30 fps is common in online video and gaming content. Higher frame rates such as 60 fps and above are used in sports broadcasting and gaming, where fluid motion is critical.
It is important to understand that frame rate and resolution are entirely separate properties. Changing the frame rate does not make an image sharper or more pixelated — it only affects how smoothly motion is rendered.
Resolution
Resolution in moving image refers to the number of pixels making up each individual frame, expressed as width × height. More pixels per frame means finer detail, sharper images, and larger file sizes. The common resolution standards are:
SD (Standard Definition) is 720 × 576 pixels. It was the broadcast standard before HD became widespread and appears soft by modern expectations, particularly on large screens.
HD (High Definition) is most commonly 1920 × 1080 pixels, also written as 1080p. This is the current standard for most online video platforms, streaming services, and broadcast television.
UHD (Ultra High Definition) is 3840 × 2160 pixels — four times the pixel count of HD. Often marketed as 4K, this is increasingly standard for modern televisions and premium streaming.
4K in its strictest cinema definition is 4096 × 2160 pixels, though the term is widely and loosely applied to UHD content as well.
8K reaches 7680 × 4320 pixels, offering extraordinary detail but requiring enormous storage and processing power. It remains a niche standard, used in high-end broadcast and future-proofing production workflows.
Higher resolutions produce richer, more detailed images but result in significantly larger file sizes, which has implications for storage, editing, and distribution.
Moving Image File Formats
Moving image files can be divided into two broad categories: video and animation. Both can be saved as either uncompressed or compressed files.
Video Formats
Video files contain footage recorded from a camera, capturing real-world motion. The most important examples to know are:
MP4 is the dominant format for online video distribution. It uses efficient lossy compression (via the H.264 or H.265 codec) to keep file sizes small while maintaining good visual quality. MP4 combines video and audio in a single file, plays on virtually every device and platform, and is well suited to streaming — making it the natural choice for social media, YouTube, and web delivery.
AVI (Audio Video Interleave) is an older Microsoft format that can store video with relatively little compression, preserving good quality. File sizes are considerably larger than MP4, making it less practical for online use, though it remains in use for editing workflows on Windows-based systems.
WMV (Windows Media Video) is another Microsoft format designed for streaming. It uses high compression to keep file sizes manageable, though it is less universally compatible than MP4 — it works best within Windows environments.
Animation Formats
Animation files contain moving images created digitally rather than recorded from life. They may be frame-by-frame drawings, computer-generated sequences, or looping motion graphics.
GIF is a widely used format for short, looping animations — particularly on social media and in web design. Its major limitation is a maximum of 256 colours per frame, which makes it unsuitable for detailed or photographic animation. It produces no sound.
SWF (Small Web Format, formerly Shockwave Flash) was historically used for interactive animations and browser-based content. It has largely fallen out of use following the decline of Adobe Flash.
HTML5 Canvas and CSS animations have largely replaced SWF for browser-based animation, though these are not single file formats in the traditional sense.
Unlock All Revision Notes
Syllabus-perfect, clutter-free summaries — so you only study what really matters.
Start your 7-day free trial (no card needed!)Existing User? Sign In