[opus] Hybrid mode and Packet Loss Concealment

Jean-Marc Valin jmvalin at jmvalin.ca
Fri Nov 30 00:21:50 PST 2012

On 12-11-28 03:31 AM, van Bijleveld Christian (ST-CO/ENG1.3) wrote:
>   * I am using as input a 48 KHz sampling rate speech file, thus full
>     band speech. I have tested several bitrates and frame sizes.
>     According to the documentation, OPUS codec will work in hybrid mode
>     when frame sizes of 10 or 20 ms are used, and bitrates from 40Kbps
>     and above. However, the configuration info generated by the tool
>     says that packets are coded either in LP mode (SILK) or MDCT mode
>     (CELT), and I cannot see any reference to hybrid mode. Further
>     reading the documentation, it says that the codec mode depends on,
>     among others, the type of signal (speech vs. music) and that
>     currently this parameter needs to be provided to the application (no
>     automatic detection). I understand from this that by default, OPUS
>     works in music mode. But there is no means to set the parameter to
>     speech at least via a command line flag. How can OPUS be configured
>     to work in speech mode for full band audio?

In general, what you probably just want to do is configure your encoder
with OPUS_APPLICATION_VOIP. Otherwise, you can be more specific and do:
opus_encoder_ctl(encoder_state, OPUS_SET_SIGNAL(OPUS_SIGNAL_VOICE));

> I also have a question regarding Packet Loss Concealment in hybrid mode:
>   * the documentation describes (section 4.4) a PLC method for CELT mode
>     and one for SILK mode. What is the PLC algorithm when OPUS works in
>     hybrid mode?

Hybrid PLC :-)


> Thanks in advance.
> Met vriendelijke groeten | Best Regards,
> *Christian van Bijleveld
> *Bosch Security Systems BV
> Bosch Communications Systems, BL Public Address and Conference Systems
> (ST-CO/ENG1.3)
> P.O. Box 80 002
> 5600 JB  Eindhoven
> The Netherlands
> _www.bosch__security.com_ <http://www.boschsecurity.com>
> T. +31 (0)40 257 7076
> F. +31 (0)40 257 7091
> _christian.vanbijleveld at nl.bosch.com_
> <mailto:christian.vanbijleveld at nl.bosch.com>
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