Changing Frame Rate

Peter Maersk-Moller pmaersk at gmail.com
Fri Jun 24 08:04:44 UTC 2016


Hi Sabastian.

Assuming you are using mp4mux with h264parse prepended and assuming the
stream could be ... lets say a RTP stream received using udpsrc, then you
can send first a stream with frame rate A (and resolution X) and then frame
rate B (and resolution Y). In theory h264parse should detect the frame rate
change and in theory, it should signal that to mp4mux and in theory mp4mux
should accept this and create a new entry describing the new condition, as
it can with resolution change in the middle of a stream. If the code is
there in mp4mux and h264parse, that ought to work.

Likewise the demuxer should be able to detect frame rate change and
resolution change and a player should be able to handle change of both
resolution and frame rate during play. However implementations may not
always be full.

Regards
PMM

On Fri, Jun 24, 2016 at 9:47 AM, Sebastian Dröge <sebastian at centricular.com>
wrote:

> On Do, 2016-06-23 at 20:03 -0700, ht techdev wrote:
> > Hi
> > Is there a way, within gst-launch, to change the frame rate on fly?
> > Failing that is it possible to append to an existing encoded file,
> > using a different rate:
> >
> > gst-launch-1.0 videotestsrc is-live=true num-frame=10 !  video/x-raw,
> > framerate=\(fraction\)”30/1” ! \ ! x264enc ! filesink location=t.mp4
> > gst-launch-1.0 videotestsrc is-live=true num-frame=10 !  video/x-raw,
> > framerate=\(fraction\)”50/1” ! \ ! x264enc ! filesink –append
> > location=t.mp4
>
> With gst-launch-1.0 you can't do it, with actual code you relatively
> easily can (you "just" change the framerate).
>
> Appending MP4 files is not easily possible, you would at least have to
> remux them but for full correctness you would also have to reencode the
> h264 stream as the avcC struct (the "header") is going to be different
> for both encodings in your case and that's not really allowed by the
> spec (there can only be one).
>
> --
>
> Sebastian Dröge, Centricular Ltd · http://www.centricular.com
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>
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