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Sound format from svxlink to Qtel

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Sound format from svxlink to Qtel

Robert

I am trying to work on a bigger project but the part that I need help with is just the format of the sound (audio) packets that comes through the UDP interface. I know where the header and data parts are but I don’t know what format the data is really in. It appears to be an integer format that is converted to float and then somehow send to be played. I want to capture the UDP packet (which I am doing) and then play the sound myself. The big problem is, I need to do it on a Windows platform. If I can just figure out the format of the byte level data, I am sure I can find a way to play it. Unfortunately, I get a bit lost following the code in qTel when it comes to playing the audio.

 

Is anyone able to help clarify this for me. Thanks in advance.

 

Robert Grimes

 


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Re: Sound format from svxlink to Qtel

Rob Janssen
Robert wrote:

I am trying to work on a bigger project but the part that I need help with is just the format of the sound (audio) packets that comes through the UDP interface. I know where the header and data parts are but I don’t know what format the data is really in. It appears to be an integer format that is converted to float and then somehow send to be played. I want to capture the UDP packet (which I am doing) and then play the sound myself. The big problem is, I need to do it on a Windows platform. If I can just figure out the format of the byte level data, I am sure I can find a way to play it. Unfortunately, I get a bit lost following the code in qTel when it comes to playing the audio.

 

Is anyone able to help clarify this for me. Thanks in advance.

 

Robert Grimes



Which UDP interface?  Do you mean the Echolink interface (UDP port 5198)?
This data is in a format that is negotiated during session setup.   Normally in Echolink it is GSM CODEC format but
svxlink also supports SPEEX format and when you connect Qtel to svxlink it will switch to SPEEX (which you can see
in the log or on standard output).   This results in better quality of the audio.

However, when you are looking at other UDP interfaces in the system, e.g. the RAW_AUDIO_UDP_DEST or the
AUDIO_DEV with type "udp", the format is different.   Look in the svxlink.conf manual page.

Rob

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Re: Sound format from svxlink to Qtel

Robert
Sorry, I should have been more specific. I am using speex. I have got the upd packet and separate the audio packets from the stream. I want to play the sound in the packet. I just can't figure out what interface in my windows code to use. I can get more specific if necessary . I will also look at the reference you gave. Thanks.

Robert Grimes

On Jan 14, 2016, at 1:51 PM, Rob Janssen <[hidden email]> wrote:

Robert wrote:

I am trying to work on a bigger project but the part that I need help with is just the format of the sound (audio) packets that comes through the UDP interface. I know where the header and data parts are but I don’t know what format the data is really in. It appears to be an integer format that is converted to float and then somehow send to be played. I want to capture the UDP packet (which I am doing) and then play the sound myself. The big problem is, I need to do it on a Windows platform. If I can just figure out the format of the byte level data, I am sure I can find a way to play it. Unfortunately, I get a bit lost following the code in qTel when it comes to playing the audio.

 

Is anyone able to help clarify this for me. Thanks in advance.

 

Robert Grimes



Which UDP interface?  Do you mean the Echolink interface (UDP port 5198)?
This data is in a format that is negotiated during session setup.   Normally in Echolink it is GSM CODEC format but
svxlink also supports SPEEX format and when you connect Qtel to svxlink it will switch to SPEEX (which you can see
in the log or on standard output).   This results in better quality of the audio.

However, when you are looking at other UDP interfaces in the system, e.g. the RAW_AUDIO_UDP_DEST or the
AUDIO_DEV with type "udp", the format is different.   Look in the svxlink.conf manual page.

Rob
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