Encoding audio and video
Digital audio and video has a sample rate, bit depth and bit rate. They are usually compressed to reduce file size and stream more efficiently over networks. Compression can be lossy or lossless.
Digital video
A digital film is created from a series of static images played at a high speed. Digital films are usually around 24 frames per second but can be anything up to around 100 frames per second or more.
Films have a frame rate per second (fps). This is similar to sample rate. HD film is normally 50 or 60 fps. This can also be measured in frequency (Hz). TV and computer screens have a specification in Hz to indicate the frame rate they support.
Digital films also have a bit rate that accounts for the total audio and image data processed every second.
Video compression
Videos are compressed in order to:
- reduce the resolution
- reduce the dimensions
- reduce the bit rate
Data lost during the compression process can cause poor picture quality or even random coloured blocks that appear and disappear on the screen. These blocks are called artefacts.
Examples of popular lossy video file formats include MP4 and MOV. Video file formats use codecs to carry out compression algorithms on the video's picture and audio data.
App developer Ivo Jansch explains why compression is used to reduce the amount of binary numbers contained within a video file