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Is that possible, that a video (.mp4 or etc) had two video streams and we could to do work with each stream individually ? (like we do with 2 audio streams and we can remove any of them)..

if so:

1) do you know which video editors can handle such videos? Adobe Premiere , Sony Vegas, DaVinci or ... ?

2) At this moment, my typical MP4 files are converted by youtube (after upload) to i.e. mpeg-4 10 AVC. And will those 2-stream videos will be converted to 1-stream video anyway? (maybe I have to ask that to YT forum, right?)

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    Certainly can. MP4 files can contain any number of video, audio, subtitle and other data tracks. – stib Mar 15 '17 at 12:15
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    In practice, yes. Although I'm sure the field storing the number of streams has a max limit of 2^16 or 32. – Gyan Mar 15 '17 at 13:00
  • @T.Todua, out of curiosity, what is your use case? – Michael Liebman Mar 15 '17 at 23:43
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Yes. MPEG-4 Part 14 (the MP4 container format) supports any number of objects (e.g. video, audio and subtitle streams) and isn't limited to only one stream per content type.

In practice however, you seldom see a video file that has multiple video streams, because the range of applications for this is very limited. I would also advise you not to put multiple video streams into one file, as (a) users don't expect it, many won't know how to switch the video track or not notice there is a second video track at all and (b) many players (soft- and hardware) aren't equipped to play files with multiple video streams and either won't have any option to switch between streams or fail to play the file completely.

It is also more common to use Matroska (.mkv) containers for video files with multiple audio/subtitle streams, but even with those, you rarely see files with more than one video stream.

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    1) do you know which video editors can handle such videos? Adobe Premiere , Sony Vegas or?... 2) will youtube convert such video file into 1-streamed file (at this moment, my typcal m4 files are converted by youtube to mpeg-4 10 AVC_ – T.Todua Mar 16 '17 at 11:14
  • Another disadvantage of multiple video streams in one file is (c) that it dramatically increases the filesize. To play one of the streams the player has to access the data for all of them at the same time. – stib Mar 16 '17 at 11:29
  • @T.Todua No idea. As I said, in my experience most applications aren't built to handle multiple video streams because in practice there's really no application for them. You should be able to build a file with multiple video streams with ffmpeg, but what is YouTube supposed to do with it? It doesn't even have an option to switch between multiple Audio streams, let alone Video streams ... just create two seperate videos and be done with it – MoritzLost Mar 16 '17 at 12:49
  • One application I think is storing footage from depth cameras (RGB-D). Synchronizing the two video tracks at a frame level could be tricky I suspect -- does .mkv support this? – thinkski Aug 2 '18 at 21:52

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