[Discuss-gnuradio] Audio Questions

[Michael Dickens]

I'm working on gr-audio-osx (MacOS X 10.4 using "CoreAudio" or a  
related framework), and have some questions.  I did a quick search of  
the email archive, but didn't come upon anything useful for this  
question in the first few pages of results (lots of other interesting  
stuff though).  Should be pretty straight forward to create a basic  
source and sink, though I do have a few (should be) simple questions.

Looking at gr-audio-oss and gr-audio-alsa, it looks like I primarily  
have to define src/audio_osx_sink.[cc,h] and src/audio_osx_source. 
[cc,h]; the other files will follow from the changes made to these  
files.

Taking "sink" as an example, it looks like what I need to do is modify

1) "audio_osx_sink::audio_osx_sink" to open and start the audio  
channels, allocate any buffers, setup audio parameters
2) "audio_osx_sink::~audio_osx_sink" to close the channels, delete  
buffers, etc...
3) "audio_osx_sink::work" to "play" the incoming data to the output  
audio channels

Questions about "audio_osx_sink::work":
int audio_osx_sink::work (int noutput_items,
  gr_vector_const_void_star &input_items,
  gr_vector_void_star &output_items)

a) It looks like the audio input (input_items) is in float's; is this  
true?

b) On CoreAudio, I can open channels to use float's as inputs, and  
thus could use the audio input ( (input_items) directly for audio  
playback.  I believe that CoreAudio doesn't copy the input buffer,  
but rather uses it as is; this can be done either a/synchronously.   
But: Do I need to copy the input data to a temporary buffer before  
playing, or will the input buffer (input_items) have a long enough  
life to allow for its playing?  Can any other subroutine use this  
buffer simultaneously, or do all subroutines need to make a copy of  
it before doing their processing?

c) When does ::work get called?  Is it on a regular period, no matter  
how much data has come in since the last time it was called?  Or when  
enough data is available to fill a given buffer size?