opus - Dec 2012 - multi stream decode

Hi,

I don't understand how works the multi stream api in opus.

I need to send two mono streams over network with RTP.

I think I'm right when I create an OpusMsDecoder with

opus_multistream_decoder_create (48000, 2, 2 ,0 ,mapping, NULL)

where mapping is:  unsigned char mapping[2] = {0,1} isn't it ?

Next, i need to encode data which I get from jack (float) so I use
opus_multistream_encode_float(enc, data, 480 , encodedData, MAX_DATA)

Then I send it using RTP.

My question is how can I make the opposite in the client.
I created my decoder with
m_decoder = opus_multistream_decoder_create (48000, 2, 2 ,0,mapping,NULL)
and
unsigned char mapping[2] = {0,1};

Currently, I can read my RTP packet from network, and get data from it. I
need now to decode opus data to something readable for jack. I do it like
that :
opus_multistream_decode_float(m_decoder, data, len, decodedBuffer, BUFLEN,
0);

But how can I know the start of the two packets ?

Thanks for your help,
Audric Ackermann
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Hi Audric,

First thing I'd like to point out is that the current RTP draft does not
support transmitting more than one stream. Unless the two streams are
truly unrelated, I recommend sending as a stereo stream using the
standard (non multi-stream) API. Otherwise, you will not be compatible
with any other application, in which case, I strongly recommend *not*
using "opus" as the SDP codec name.

On 12/18/2012 10:21 AM, Audric Ackermann wrote:
> I think I'm right when I create an OpusMsDecoder with
> 
> opus_multistream_decoder_create (48000, 2, 2 ,0 ,mapping, NULL)
> 
> where mapping is:  unsigned char mapping[2] = {0,1} isn't it ?
> 
> Next, i need to encode data which I get from jack (float) so I use
> opus_multistream_encode_float(enc, data, 480 , encodedData, MAX_DATA)
Looks correct.
> My question is how can I make the opposite in the client.
> I created my decoder with
> m_decoder = opus_multistream_decoder_create (48000, 2, 2
> ,0,mapping,NULL) and
> unsigned char mapping[2] = {0,1};
> 
> Currently, I can read my RTP packet from network, and get data from it.
> I need now to decode opus data to something readable for jack. I do it
> like that :
> opus_multistream_decode_float(m_decoder, data, len, decodedBuffer,
> BUFLEN, 0);
Also looks correct.
> But how can I know the start of the two packets ?
I don't understand your question.

	Jean-Marc

On Tue, Dec 18, 2012 at 10:21 AM, Audric Ackermann
<audric.bilb at gmail.com> wrote:
> Currently, I can read my RTP packet from network, and get data from it. I
Multistream is not used with RTP as defined today.  The multistream
support requires a mechanism to communicate the mapping, see the
Ogg/Opus draft for an example of his this is actually used.

What you appear to be describing is just stereo? however. You don't
use multistream fo stereo, you can just use a single stereo stream.
Using multistream for stereo will make you incompatible with
everything RTP based.