On 22/12/2015 10:11, Carl Eugen Hoyos wrote:
Jean-Marie Baran <jean-marie.baran <at> ama.bzh> writes:
What I try to achieve here is to have Ffmpeg somehow
record the variation in the framerate. Ideally I
would tell it, «well, record the timestamp of the
frame as they arrive»,
Which timestamp are you talking about?
stdint cannot provide timestamps and is
read as fast as possible.
Where does the mjpeg stream originate?
Whatever it is, you should try to use it
as input for FFmpeg, maybe it provides
timestamps...
Carl Eugen
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The stream comes from a third-party application which sends at an
approximate rate of 15fps. It sends raw MJPEG frames alternated with
metadata which contains only the size of the next frame :
| size of next frame | MJPEG frame | size of next frame | MJPEG frame |
size of next frame | MJPEG frame | ...
My program reads this, remove the sizes, and send the frames on ffmpeg's
stdin. So indeed ffmpeg reads as fast as the frames arrive, which is
approximatively 15fps, but record a fixed frame rate of 15fps in the
mp4. For example, if "|" is the moment at which a frame arrives, and "-"
is a unit of time, the frames could arrive on stdin like this:
|---|--|-|--|----|-----|----|---|---| (1)
And ffmpeg will record it like this:
|---|---|---|---|---|---|---|---|---| (2)
So when playing back the video, at some moment it seems it is played too
quickly, at others too slowly. If that is possible, I would like ffmpeg
to record this irregularities into the mp4, so that players do not play
the video as it were a fixed frame rate.
On a side note, I imagined ffmpeg would be able to detect the fps (hence
my first question about removing "-r 15"), but I was wrong.
--
*Jean-Marie Baran*
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