[alsa-devel] Exemple of source code for capture without using callback
Hi all,
it's my first time on this list and my knowledge about using poll() mutex and thread creation is a bit far away from now, so please, if this list is the wrong place for such a question, could you point me in the right direction?
Does anyone can point me a place to find a good exemple of source code for capturing sound with alsa without using callbacks?
I'm trying to interface a voice recognition software with the alsa drivers.
I have to get audio from alsa convert it and then send to the recognition engine. I've read everywhere that using callback is a bad method to use the alsa drivers.
As the recognition software is a server, it needs to be synchronized with my application. And so my main() cannot loop on a endless loop with the snd_pcm_readi() function inside.
My first idea was to create a new thread and to let this thread running with a endless loop that do the snd_pcm_readi() and send the buffer to the recognition software. But I 've read the existence of smd_pcm_poll_descriptors() function. For now I not shure was it is for and how to use it properly.
What do you think?
I'm sorry if my question is a real newbie question, but exemple online are only for playback not capture.
Many thanks for all your answers.
Bruno.
2009/10/20 brunal2496 gmail brunal2496@gmail.com:
I'm trying to interface a voice recognition software with the alsa drivers.
I have to get audio from alsa convert it and then send to the recognition engine. I've read everywhere that using callback is a bad method to use the alsa drivers.
This is wrong. callback is the best method. With current distributions all doing pulseaudio, it would probably be better interfacing with pulse. If you need a more professional real time interface, use jackd interface. For what you need, jackd is probably the simplest api to use.
James Courtier-Dutton wrote:
2009/10/20 brunal2496 gmail brunal2496@gmail.com:
I've read everywhere that using callback is a bad method to use the alsa drivers.
This is wrong. callback is the best method.
But _not_ the snd_async_add_pcm_handler function, which is evil. (This is the only ALSA PCM function that mentions "callback" in its documentation, so these are often confused.)
The 'good' callback method means that the audio driver informs the application when its wants to have new audio data, not the other way.
Best regards, Clemens
2009/10/22 Clemens Ladisch clemens@ladisch.de:
James Courtier-Dutton wrote:
2009/10/20 brunal2496 gmail brunal2496@gmail.com:
I've read everywhere that using callback is a bad method to use the alsa drivers.
This is wrong. callback is the best method.
But _not_ the snd_async_add_pcm_handler function, which is evil. (This is the only ALSA PCM function that mentions "callback" in its documentation, so these are often confused.)
The 'good' callback method means that the audio driver informs the application when its wants to have new audio data, not the other way.
Yes, to clarify, not that call. A poll() that then does the callback is the preferred method.
Tanks for your answer.
But _not_ the snd_async_add_pcm_handler function, which is evil. (This is the only ALSA PCM function that mentions "callback" in its documentation, so these are often confused.)
The 'good' callback method means that the audio driver informs the application when its wants to have new audio data, not the other way.
If I'm not wrong you're talking about playback in that case, isn't it? I'm considering capture so you mean that the good callback method is when the audio driver tells the application that it have new audio data (the buffer contains at least a "period_size" of audio samples) to give to it. Am I right?
Yes, to clarify, not that call. A poll() that then does the callback is the preferred method.
Ok. But I cannot find a source code using poll() for capture on internet. Would you please gimme a pointer or at least a pseudo-code for an application using poll() i.e. just what is the sequence of the function? Many thanks.
participants (3)
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brunal2496 gmail -
Clemens Ladisch -
James Courtier-Dutton