[FFmpeg-user] mjpeg stream

[Carl Eugen Hoyos]

2019-01-16 20:25 GMT+01:00, Gabriel Zachmann <zach at cs.uni-bremen.de>:
> I would love to get some insights.
>
> I have a video that contains 3 streams (see below for the full output of
> ffprobe).
> This is causing me a bit of a headache.
>
> My questions are:
> -  what is Stream #0.2

It is a low-quality sample frame from the original video,
you can extract it (for example) with:
$ ffmpeg -i input -map 0:2 -vcodec copy out.jpg

> ? is it the same video footage as Stream #0.0, except
> in a different codec ?

No, it is just one frame.

> why is it there?

Possibly to allow a peek into the content of the video.

> -  can I just delete it, or is it necessary to view the video as a whole?

You can not easily "delete" it because it part of a multimedia file
(that is typically non-trivial to edit) but it is not necessary and
if you create a new multimedia file with the same audio and same
video as your file, you can choose not to copy the still frame.
(In this case, you have not "deleted" it because you have created
a new file with certain different properties.)
Note that the single frame is 127k of 32M.

> -  when converting the video (as a whole) , should I convert it , too, or
> just copy it? or can I safely omit it?

You can omit it if you don't need it.

> -  Can I assume that if there is a second video stream in a file, then it is
> usually not really needed?

No, stereo presentations and presentations with a stream showing sheets
and another stream showing the presenter exist (for example).

> -  If yes, can I assume that the second video stream is usually the one that
> could be omitted?

> -  in Quicktime Player 7, I can see only one video track - why don't I see
> two tracks?

There should be directory viewers that should show you the still
frame instead of a general symbol.

Carl Eugen