[opus] Question on opus_decoder output sampling rate

Jean-Marc Valin jmvalin at jmvalin.ca
Thu Apr 2 07:46:16 PDT 2015

The encoder and decoder can handle, 8, 12, 16, 24 and 48 kHz
input/output. If doesn't matter what it gets encoded to/decoded from.
you can initialize a decoder at 8 kHz and it'll still decode 48 kHz
audio fine (you just won't get the high frequencies obviously). For
sampling rates other than 8/12/16/24/48, then you'll have to do
resampling. Have a look at the speexdsp resampler if you don't already
have one.



On 02/04/15 10:42 AM, Julien Chavanton wrote:
> Hi, is there any way to tell the decoder the output sampling Fz we want ?
> opus_decoder_create = Sampling rate of input signal (Hz)
> Considering this example (VoIP-out from WebRTC/RTP)
> MICROPHONE(44.1/48kHz) >> [encoder created at 48kHz but with
> internalSampleRate set to 8kHz]>> INTERNET >> [decoder(created with
> 48kHz)] >> 48kHz(?) >> G.711(8kHz)
> This leaves us with the only option to re-sample even if the internal
> sample rate was set to 8kHz.
> This may not seem like a big problem since we could simply resample but
> on a server with a lot of load this could be significant ?
> https://tools.ietf.org/html/draft-ietf-payload-rtp-opus-08
> Is not very clear on these points.
> Regards
> Julien
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