On Thu, 13 Mar 2008 18:16:13 +0100
John Sigler <linux.kernel@xxxxxxx> wrote:
> Hello,
>
> I've been struggling with alsa-lib for about a week, mainly trying to
> come up with the appropriate configuration file.
>
> I'd like to describe what I'm trying to do, so that ALSA users might
> tell me whether the ALSA infrastructure is the correct tool for the
> app I'm writing.
>
> Consider two systems A and B in separate physical locations, both
> connected to some kind of network.
>
> A is considered the "sender" because it captures audio, and sends it
> to B, while B is considered the "receiver" because it receives the
> data sent by A, and plays it back.
>
> The code running on A is conceptually simple:
>
> while ( 1 )
> {
> capture a packet's worth of data (e.g. 1024 bytes)
> add some information in a header
> send the datagram to B
> }
>
> The input is an AES signal. I've been told that it is very rare for
> capture boards to provide the raw AES frames. Is this correct? If it
> is true, the board would capture the AES payload (either PCM or
> compressed Dolby E).
>
> Now, to add some complexity, I'm considering a board with multiple
> inputs, to be able to run many processes in parallel.
>
> (I have an RME AES-32 board which provides 8 AES inputs.)
>
> On B, the code is more complex, because the issue of synchronization
> rears its ugly head.
>
> B is trying to playback the stream sent by A, with a small time shift
> (e.g. 200 ms) at the exact same rate that it was captured by A. This
> means the code needs to buffer a number of audio frames, then start
> the playback, and monitor the level of the hardware buffer to
> determine whether that buffer is slowly emptying or filling up. Every
> time B receives data from A, it pushes the data to the board's
> hardware buffer. To keep the level constant, it might need to add or
> remove a few frames once in a while.
>
> The AES-32 board also provides 8 AES outputs, so I'd use another such
> board on B. There might be several streams played back at the same time.
>
> What is your opinion / thoughts on this architecture?
>
Have you thought of using bigger pieces like jackd/jack-diplomat,
named pipes + netcat ?
Regards,
Sergei.
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