Re: [FFmpeg-devel] [PATCH] avformat/rtpenc: Add flag AVFMT_NODIMENSIONS.

From: Koushik Dutta <koushd@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] avformat/rtpenc: Add flag AVFMT_NODIMENSIONS.
Date: Fri, 28 Mar 2025 23:30:05 -0700
Message-ID: <CAO4LPj_nUcjKYMpcA5OFa1nzRH=ya-nU9V3AgpU-aVRca_B-Uw@mail.gmail.com> (raw)
In-Reply-To: <20250328233922.GM4991@pb2>

Yes, that’s what I am doing. I am repacketizing h264 and hevc without
inspection of the stream itself. RTSP over tcp can transmit rtp packets up
to 64k. Some cameras utilize this to reduce fragmentation overhead but
those large packets need to be fragmented for udp rebroadcast on typical
network mtu.

I could inspect the stream for sps and then parse the dimensions out of
there, or maybe set some dummy values on the rtp encoder somehow and work
around this. But neither of those seemed like proper solutions given rtp
doesn’t need to know the steam dimensions for all but 2 codecs.

On Fri, Mar 28, 2025 at 4:39 PM Michael Niedermayer <michael@niedermayer.cc>
wrote:

> Hi
>
> On Wed, Mar 26, 2025 at 01:13:13PM -0700, koushd@gmail.com wrote:
> > From: Koushik Dutta <koushd@gmail.com>
> >
> > Not all rtp formats require the video dimensions to be available
> > up front. H264 and HEVC will send them as stream parameters.
> > The flag is restrictive and prevents RTP repacketization
> > without parsing the codec information out of the stream.
> >
> > This change checks to see if the codec parameters are available
> > on the rtp formats that need it.
> >
> > Signed-off-by: Koushik Dutta <koushd@gmail.com>
> > ---
> >  libavformat/rtpenc.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
>
> In general when muxing a stream, the dimensions are known
>
> Can you explain what you are doing with rtpenc that lacks
> known dimensions ?
> is this some sort of low latency remuxing ?
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Some people wanted to paint the bikeshed green, some blue and some pink.
> People argued and fought, when they finally agreed, only rust was left.
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