Stuart,
Some things that might help:
- I'm currently working on a number of small tools that capture /
playback audio with codec2 encoding and UDP transport.
Althou it is designed to be part of the c2_gmsk modem package (having a
modem is nice, but you also need to have a tool to capture the voice and
play it back); these tools can also be used to send/receive
codec2-encoded stream between any two hosts.
If all goes will, I should be able to release some more development code
this weekend, together with a "how to compile / install" text.
- real-time codec2 encoding and decoding does indeed work without an
issue; using about 20 % of the CPU of the pi.
- There DO are some other issues on the pi.
As you mention indeed, there is no audio input on the pi. You need to
use a USB audio-dongle for that.
However, there seams to be a problem on the ALSA layer with USB audio
input at 48000 Kbps (as used by the gmsk modem). When using portaudio
(which uses ALSA) with callback functions, I still have about 1.5 % loss
of "lost frames" on the audio layer.
This is a lot better then when using blocking I/O but still "not good".
It should be zero % "lost frames".
Audio output can be done using the onboard audio-interface and that one
does not have this issue.
In short. If we manage to get the audio lost-frames issue under control,
the raspi should surely be a nice device for codec2 based applications.
73
kristoff - ON1ARF
On 14-12-12 17:41, Stuart Marsden wrote:
It does not have native audio input but USB sound should work. Not
tried it yet though I just used a raw file to see if it was fast
enough. I plan to use a USB Skype phone for my application.
Stuart
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