I understand why there might be multiple audio and/or subtitle tracks in an MP4 file. But, it would seem that multiple video tracks is a possibility, although I have only seen them in a DVD. I have seen where multiple titles in a DVD can each have separate chapters. But, I don't quite understand why you would want to have multiple video tracks in an MP4. Can anybody give me examples of where that is useful?
If I were to have multiple video tracks in an MP4, I imagine that each track would want/need to have an associated set of chapters, audio track, and, possibly subtitle tracks. Can anybody point me to a site/sites that explains and talks about the issues and processes necessary to deal with multiple video tracks?
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Can anybody give me examples of where that is useful?
They are usually used to store stream with different resolutions or angles, basically the same you would do on DVD or Blu-ray.
(iirc. in .mpd files also use something similar to pack multiple parts into one file, you might have some luck looking into this when searching for DASH.)
If I were to have multiple video tracks in an MP4, I imagine that each track would want/need to have an associated set of chapters, audio track, and, possibly subtitle tracks.
So this would only work with a custom player and some custom (non-standard) additional stream holding the mapping.
Cu Selurusers currently on my ignore list: deadrats, Stears555
I have read about DVDs that have both the fullscreen and widescreen versions on the same disc. In that case, the chapters, audio, and, subtitle tracks would obviously match up without any other considerations. The only other possibility that I could think of was the the 1985 film "Clue the Movie". It was based on the board game and had three different endings. In the theaters, they only showed one of the endings and the theaters did not advertise which ending they were showing. I have the DVD and just looked at it. They resolved the issue by showing the first ending, then, show a panel that says something like "or, it could have happened this way" and went on to show the next ending.
I recently purchased the "Heavy Metal" DVD and it has two main titles. Both of them have a different number of chapters. But, there is only one video track shown. That may mean that each title only has one video track. Otherwise, I have always tried to purchase the widescreen versions of DVDs, so, I don't know if I have one that has both the fullscreen and widescreen versions on the same disc.
The possibility of an additional video track was just something I noticed in VLC and couldn't come up with a good reason for it. I guess it is a trade-off where VLC wants to accommodate both DVDs and computer videos. Maybe someday when I have nothing better to do, I will try adding a second video track to an MP4 file - and I will make sure that I have a fire extinguisher handy
Multiple tracks has uses with stereoscopic video. However, again, without being designed with a specific playback standard, it might be a crap shoot how apps support it.
Btw, I have tested all the major containers and they can all support it, more or less.
VLC, they do not show that multiple video tracks are available. Do you know where I can download some stereoscopic videos with multiple video tracks so that I can see what is going on?
Sorry, it's crunch time on campus right now, so I'll have to get back to you in a few days...