hello, i’m trying to understand what a video file format is and if it’s any different then a video container format, for example
mp4
mv4
mkv
.webm
.flv
.ogg
.gif
.avi
.mov
are these all “video file formats” or video container formats? if these are container formats then what is the video file format of each of them and the difference between the video file format and the container format?
thank you
In: 3
Video file formats are based on containers, containers are not always video file formats.
MPEG-2 TS is intended to be sent over a network, and can be played from the middle of a stream, so it’s considered a container. When written to disk as a mp2ts file, it is a file format.
Some containers (MP4) are made to save to a disk, and store the information about what codec was used, and information on how to feed the decoder, usually at the end (moov atom), and thus is considered a file format.
In more detail:
Video and audio is a lot of data, and it has to be made smaller (encoded).
There are lots of ways to make it smaller (codecs).
Sometimes people want to send video to other people, so they can play them over an antenna, or the internet, without downloading them entirely.
Sometimes they want to save their video to a disk, to play later.
When video and audio are played it has to be made bigger again (decoded), and it has to be played together correctly (synchronized). Containers store the information on how to perform both of these things, as well as synchronize other data (subtitles for instance).
Networks send data in small units, files are read in chunks and not completely into memory, and decoders need that data on very specific boundaries depending on the codec used.
Some containers (MPEG2 TS) are made to send video and audio over a network in tiny packets, and to allow people who start listening to those packets anywhere in the middle to put those packets together into the right sizes, to synchronize them, and to know how that data was compressed (codec), so that they can decode them without having seen the whole stream.
Some (MPEG4) are made to be played directly from a disk, and require the player seek (potentially the entire file) for information they need to decode and play the encoded streams it contains.
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