[FFmpeg-devel] [PATCH] Implement an option in ffmpeg to make it print the output SDP and exit

Luca Abeni lucabe72
Wed Jul 16 08:38:54 CEST 2008

Hi Stefano,

Stefano Sabatini wrote:
> Hi all,
> this patch changes the current behavious of ffmpeg which currently
> print if needed the SDP of the output streams.

Michael is ffmpeg.c maintainer, but since I am the one who
implemented SDP output I have some comments.

First of all, thanks for the patch: I believe the "-sdp" option is
needed (and I've been lazy not implementing it :).

> This patch implements a behaviour which could result useful when
> scripting things like this:
> ffmpeg  -i ~/test.avi -vn -sdp -f rtp rtp://localhost:5004 > test.sdp
> ffplay test.sdp
> ffmpeg  -i ~/test.avi -vn -f rtp rtp://localhost:5004 > test.sdp
> Since I think this is the assumed use for the SDP output then I think
> this behaviour is preferable since it doesn't require the user to
> invoke a transcoding just to print out the SDP.

I generally use "-t 0.001" if I want to generate the SDP without actually
streaming anything.

> Note that this breaks compatibility with the previous behaviour, now
> when ffmpeg is invoked without -sdp it won't print the SDP anymore.

I think this is ok.

> Also the SDP printed won't be prefixed by "SDP:\n" as before.

I believe this is ok too.

> Comments/suggestions are welcome as always.

In my opinion, it would be more useful to have a "-sdp" option that
prints the SDP without exiting (if the user wants ffmpeg to exit
immediately after printing the SDP, he can use "-t 0.001").
But I have no strong opinions about this: if other people think that
"-sdp" should exit, I am ok with it.

Another small comments about your patch: since the SDP is now
printed when "-sdp" is specified, maybe the want_sdp variable can
be removed? Or, at least it can be merged with print_sdp_and_exit:
make it global, set it to 0 by default (and set it to 1 when "-sdp"
is used), and set it to 0 if the output format is != "rtp" (as
currently done for want_sdp).


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