Re: [Sip-implementors] Video Codec presentation in SDP-Offer/Answer

[Alan Ford]

> On 6 Oct 2016, at 18:48, Dale R. Worley  wrote:
> 
> Sachin Rastogi  writes:
>> I have a User Agent, which can decode H.264-HP as well as H.264-BP. But it
>> can encode only H.264 BP. So how should I share my offer in SDP
> 
> Clearly, you can only express this in SDP by providing two different
> m-lines, one for the send codec and one for the receive codecs.  (Which
> you could bundle.)  The problem that I see is that very few devices will
> be prepared to split sending and receiving of a video channel on
> different m-lines, they will be looking for one sendrecv m-line that
> they find acceptable.

Indeed; I’ve never met any SIP device that would handle two video m-lines like 
that.

Although it’s a bit laborious, probably the most compatible way of doing this 
is to offer both HP and BP in a single sendrecv m-line. If the far end supports 
BP, you’re all good, and can send BP to them, and they could choose to send HP 
to you if they want. The only problem would occur if the far end offered only 
HP. At that point, you should re-INVITE without HP support, and see what 
happens - the far end may at that point decide it supports BP after all, or it 
may zero port it if it doesn’t support BP at all. Which is probably the result 
you’d expect. If one-way video was acceptable, you could re-INVITE again as 
sendonly HP, but that would seem a very niche case.

Incidentally, HP can decode CB, so if you can encode as CB you could send that 
if the far end claimed to only support HP.

Regards,
Alan

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Re: [Sip-implementors] Video Codec presentation in SDP-Offer/Answer

[Dale R. Worley]

Sachin Rastogi  writes:
> I have a User Agent, which can decode H.264-HP as well as H.264-BP. But it
> can encode only H.264 BP. So how should I share my offer in SDP

Clearly, you can only express this in SDP by providing two different
m-lines, one for the send codec and one for the receive codecs.  (Which
you could bundle.)  The problem that I see is that very few devices will
be prepared to split sending and receiving of a video channel on
different m-lines, they will be looking for one sendrecv m-line that
they find acceptable.

You might have one sendrecv m-line for H.264-BP and a separate recvonly
m-line for H.264-HP.  That maximizes the chance that the far-end UA will
accept the SDP, but only my making it easy to use H.264-BP.

Dale
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Re: [Sip-implementors] Video Codec presentation in SDP-Offer/Answer

[Paul Kyzivat]

On 10/6/16 12:40 AM, Sachin Rastogi wrote:

Hi Everyone,

I have a User Agent, which can decode H.264-HP as well as H.264-BP. But it
can encode only H.264 BP. So how should I share my offer in SDP

Option 1 :

m=video 2300 RTP/AVP 100 109
a=rtpmap:100 H264/9
a=fmtp:100 profile-level-id=640029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=rtpmap:109 H264/9
a=fmtp:109 profile-level-id=428029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=sendrecv

Option 2 :

m=video 2300 RTP/AVP 100 109
a=rtpmap:100 H264/9
a=fmtp:100 profile-level-id=640029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=rtpmap:109 H264/9
a=fmtp:109 profile-level-id=428029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=recvonly

m=video 2300 RTP/AVP 109
a=rtpmap:109 H264/9
a=fmtp:109 profile-level-id=428029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=sendonly


I think the only way to negotiate asymetric codec usage is with two 
m-lines, as you show in (2).


You could however get them on a single 5-tuple by using 
draft-ietf-mmusic-sdp-bundle-negotiation-32.


The downside of this is that it probably won't interoperate well with 
legacy video devices.


Thanks,
Paul

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[Sip-implementors] Video Codec presentation in SDP-Offer/Answer

[Sachin Rastogi]

Hi Everyone,

I have a User Agent, which can decode H.264-HP as well as H.264-BP. But it
can encode only H.264 BP. So how should I share my offer in SDP

Option 1 :

m=video 2300 RTP/AVP 100 109
a=rtpmap:100 H264/9
a=fmtp:100 profile-level-id=640029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=rtpmap:109 H264/9
a=fmtp:109 profile-level-id=428029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=sendrecv

Option 2 :

m=video 2300 RTP/AVP 100 109
a=rtpmap:100 H264/9
a=fmtp:100 profile-level-id=640029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=rtpmap:109 H264/9
a=fmtp:109 profile-level-id=428029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=recvonly

m=video 2300 RTP/AVP 109
a=rtpmap:109 H264/9
a=fmtp:109 profile-level-id=428029; packetization-mode=1; max-mbps=245760;
max-fs=8196
a=sendonly

Please provide your view and if possible any reference.

Thanks & Regards,
Sachin Rastogi
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