[FFmpeg-devel] [PATCH] sdp: Add a framesize attribute to H263 SDP descriptions

Martin Storsjö martin
Mon Dec 20 14:08:24 CET 2010

Hi Luca,

On Mon, 20 Dec 2010, Luca Abeni wrote:

> On 12/20/2010 01:42 PM, Martin Storsjo wrote:
> > While not mentioned in RFC 4629, this is required for H263 in
> > 3GPP TS 26.234.
> Is it really mandatory? I seem to remember it was optional...
> But I might be wrong.

Quoting from the 3GPP spec:

    For H.263 streams, a PSS server shall include the "a=framesize" field 
    at the media level for each stream in SDP, and a PSS client should 
    interpret this field, if present. Clients should be ready to receive SDP 
    descriptions without this attribute.

So depending on the interpretation of "shall", it's more or less 

> Anyway, I think we already discussed this some time ago...
> I think setting framesize in this way is not correct (it should
> be the maximum possible frame size in the session).

Yes, we've discussed it before, but then I didn't know about any players 
actually requiring it - now I've stumbled upon such ones.

Do we btw normally support muxing streams with varying frame size? We've 
got the same issue for all other formats that transmit the frame size 
implicitly in extradata in the SDP (such as H264 or MPEG4).

> I am not against this patch, but I believe that a comment
> is needed to explain that this code is not 100% correct, and
> why this is better than nothing (mentioning the Android and
> Samsung phones).

// Martin

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