Audio transcode

Julien

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Sep 14, 2021, 6:25:21 AM9/14/21

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Hi everyone,

I successfully developed a TTS plugin on unimrcp server.

However, I have a question about the audio steaming function. The TTS server generates 16bits linear pcm 16kHz whereas I need PCMA.

Is UniMRCP server/SofiaSip able to do the job?

Yours sincerely,

Julien BAUMGARTEN

Lewis Bergman

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Sep 14, 2021, 7:38:05 AM9/14/21

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You mean something like this from page 14 of the manual?

<codecs>20 PCMU PCMA L16/96/8000 telephone-event/101/8000</codecs>

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Lewis Bergman

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Julien

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Sep 17, 2021, 1:56:27 AM9/17/21

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Hi Lewis,

Exactly BUT this information defines the codec used in the RTP stream.

My TTS engine provides linear PCM 16bit 16kHZ and I need to stream in PCMA.

I defined PCMA in codecs section of unimrcpserver.xml file BUT I need to convert and resample the stream coming from the engine.

mayamatakeshi

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Sep 17, 2021, 3:07:52 AM9/17/21

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On Fri, Sep 17, 2021 at 2:56 PM Julien <julien.b...@viatelecom.com> wrote:

Hi Lewis,

Exactly BUT this information defines the codec used in the RTP stream.
My TTS engine provides linear PCM 16bit 16kHZ and I need to stream in PCMA.

I defined PCMA in codecs section of unimrcpserver.xml file BUT I need to convert and resample the stream coming from the engine.

I never wrote a unimrcp plugin but I was expecting unimrcp headers to define some helper functions that would be commonly used by plugins.

To resample from 16000 to 8000, I would get every 2 samples, sum them and divide by 2.

Then if a function to convert from linear16 to PCMA (a-law) is not available, I would try to use linear2alaw() from here:

http://web.mit.edu/audio/src/build/i386_linux2/sox-11gamma-cb/g711.c

Julien

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Sep 17, 2021, 5:22:34 AM9/17/21

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Hi,

Thank you for your answer.

I am able to resample by using lib soxr and convert with linear2alaw function but I was looking for a "out of the box" solution.

If unimrcp server is not able to act like a bridge, i'll keep that solution.

Thx all :)

Arsen Chaloyan

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Oct 9, 2021, 2:56:26 PM10/9/21

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Hi Julien,

There is no integrated resampler in the MPF layer, even though that was provisioned originally.

In general, you are supposed to specify the capabilities of your plugin/engine while creating a new channel.

https://github.com/unispeech/unimrcp/blob/master/plugins/demo-synth/src/demo_synth_engine.c#L217

The specified capabilities are taken into account for negotiating codecs in the scope of SDP offer/answer and composing a media path.

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