opus - Sep 2017 - Force Opus/CELT to encode 2 mono instead of 1 stereo

Hi, folks,

I have an old CELT thing that I'm updating to Opus and I'm trying to get
individual pieces upgraded.  My first task is upgrading the CELT encoder
to Opus.

The old CELT thing treated the L and R channels as independent mono
streams, encoded them somehow with CELT to form one bitstream, sent one
bitstream across, and then unpacked it manually after the decoder.

Can I do that with Opus?

Right now, I'm choosing OPUS_APPLICATION_RESTRICTED_LOWDELAY in order to
only use the CELT subsystem.  However, I'm getting a lot of bleedthrough
on the stereo channels which I didn't get before.  Is there a magic
setting to adjust this?

Thanks,
-a

On 2017-09-25 10:24 AM, Andrew P. Lentvorski wrote:
> The old CELT thing treated the L and R channels as independent mono
> streams, encoded them somehow with CELT to form one bitstream, sent one
> bitstream across, and then unpacked it manually after the decoder.
You can try calling `opus_encoder_ctl(enc, OPUS_SET_FORCE_CHANNELS(2))` 
on the encoder context. That will prevent the encoder from producing 
mono packets when it thinks that's a more efficient representation of 
the signal.

Does upping the bitrate help?

In general, I suspect the answer is no. The opus encoder expects to 
exploit correllations between the two channels when given them, so it's 
not too surprising there's bleed-through at low bitrates. The general 
expectation is that applications will use distinct codec contexts for 
uncoupled streams, or for coupled streams with more that two channels.

  -r

At very low bitrate (e.g. < 32 kb/s) the encoder can't preserve all the
stereo width. But if you're encoding at higher bitrates, then there
should be absolutely no energy leakage across channels (it's actually
enforced by the bitstream(.

	Jean-Marc

On 25/09/17 01:24 PM, Andrew P. Lentvorski wrote:
> Hi, folks,
> 
> I have an old CELT thing that I'm updating to Opus and I'm trying
to get
> individual pieces upgraded.  My first task is upgrading the CELT encoder
> to Opus.
> 
> The old CELT thing treated the L and R channels as independent mono
> streams, encoded them somehow with CELT to form one bitstream, sent one
> bitstream across, and then unpacked it manually after the decoder.
> 
> Can I do that with Opus?
> 
> Right now, I'm choosing OPUS_APPLICATION_RESTRICTED_LOWDELAY in order
to
> only use the CELT subsystem.  However, I'm getting a lot of
bleedthrough
> on the stereo channels which I didn't get before.  Is there a magic
> setting to adjust this?
> 
> Thanks,
> -a
> 
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> http://lists.xiph.org/mailman/listinfo/opus
>