What is video bitrate?
The bitrate of a file is measured by the number of bits being transmitted over a period of time. For video it is typically measured in kilobytes per second (kbps) or megabytes per second (mbps).
The bitrate of a video is most influenced by the size and quality of the video being transmitted. As an example a 4K video (3840 x 2160) has over 8 times as many pixels per frame than a HD video (1280x720) (8.2M pixels vs 921kpixels), and will therefore have a higher bitrate (assuming similar compression settings for both videos). (See table below for the bitrates delivered by api,video.)
Different compression codecs have a large effect on bitrate. As video compression algorithms improve, videos can be compressed more and more at the same quality, lowering the bitrate of the video. As an example VP9 files are ~50% smaller than VP8, and AV1 files are 30% smaller than VP9 For this reason, new codecs are under constant development.
If a video's bitrate exceeds the throughput of the network, the video will stall - it will playback faster than it can be downloaded.
Adaptive Bitrate Streaming (ABS)
ABS is the ability of the video player to identify the display size, and the network capability of the device - and request a version of the video that will play for the end user.
Bitrate at api.video
At api.video, all uploaded videos are converted into Adaptive Bitrate Streams. currently, our streams are encoded as follows:
|Resolution||FPS||Video Bitrate||Audio Bitrate|
|240p||18||250 KBPS||96 KBPS|
|360p||25||800 KBPS||128 KBPS|
|480p||25||1400 KBPS||128 KBPS|
|720p||25||2600 KBPS||128 KBPS|
|1080p||30||4400 KBPS||128 KBPS|
|2160p (4k)||60||16000 KBPS||128 KBPS|
This ensures that even on the slowest network connections, video can be played. Typically video players will pick a video bitrate that matches the screen size or 80% of the available network speed.