I’m currently on a project that involve disabled peoples, audio and kinect. Theses boys and girls are doing lot of loud sounds, so the idea is to use their sound as a trigger. We can use gstreamer to make that work quite easily, cause it have everything we need: a audio source, and level calculator.
import pygst pygst.require('0.10') import gst, gobject gobject.threads_init() pipeline = gst.parse_launch( 'pulsesrc ! audioconvert ! ' 'audio/x-raw-int,channels=2,rate=44100,endianness=1234,' 'width=32,depth=32,signed=(bool)True !' 'level name=level interval=10000000 !' 'fakesink') level = pipeline.get_by_name('level') bus = pipeline.get_bus() bus.add_signal_watch() def show_peak(bus, message): # filter only on level messages if message.src is not level: return if not message.structure.has_key('peak'): return # read peak print 'peak', message.structure['peak'][0] # connect the callback bus.connect('message', show_peak) # start the pipeline pipeline.set_state(gst.STATE_PLAYING) ctx = gobject.gobject.main_context_default() while ctx: ctx.iteration()
The output could be something like this :
peak -35.2370719856 peak -35.0252114393 peak -10.8591229158 peak -4.6007387433 peak -4.85102463679 peak -6.45292575653 peak -6.83102903668 peak -7.39486319074 peak -13.9852340247 peak -17.423901433 peak -35.0852178272 peak -35.8725208237
Next, we can use that information to record their sound, and use it on some scenario. So, instead of use the fakesink, we can use appsink. This module allow you to read the buffer pushed by the previous module. So we can put theses buffers into a list, and use them when needed 
The state machine will handle the 3 phases :
- Wait for a peak > -30db
- Recording the sound, stop when the peak is < -32db
- Replay the last sound
Note: The -30 / -32 are taken from my tests. If you have more noise, you need to adjust theses triggers.
And here is the final example:
import pygst pygst.require('0.10') import gst, gobject gobject.threads_init() pipeline_play = None pipeline = gst.parse_launch( 'pulsesrc ! audioconvert ! ' 'audio/x-raw-int,channels=2,rate=44100,endianness=1234,' 'width=32,depth=32,signed=(bool)True !' 'level name=level interval=10000000 !' 'appsink name=app emit-signals=True') state = 'wait' peak = -99 buffers = [] level = pipeline.get_by_name('level') app = pipeline.get_by_name('app') bus = pipeline.get_bus() bus.add_signal_watch() def show_peak(bus, message): global peak # filter only on level messages if message.src is not level: return if not message.structure.has_key('peak'): return # read peak peak = message.structure['peak'][0] def enqueue_audio_buffer(app): buffers.append(str(app.emit('pull-buffer'))) def play_sample(sample): global pipeline_play with open('audio.dat', 'wb') as fd: fd.write(sample) if pipeline_play is None: pipeline_play = gst.parse_launch( 'filesrc location=audio.dat !' 'audio/x-raw-int,channels=2,rate=44100,endianness=1234,' 'width=32,depth=32,signed=(bool)True !' 'audioamplify amplification=2 ! autoaudiosink') pipeline_play.set_state(gst.STATE_NULL) pipeline_play.set_state(gst.STATE_PLAYING) # connect the callback bus.connect('message', show_peak) app.connect('new-buffer', enqueue_audio_buffer) # start the pipeline pipeline.set_state(gst.STATE_PLAYING) # main loop ctx = gobject.gobject.main_context_default() while ctx: ctx.iteration() print state, peak # wait for somebody to make a sound if state == 'wait': if peak > -30: state = 'record' continue # discard any buffer buffers = [] # record the current audio, until the peak is going down elif state == 'record': if peak < -32: state = 'replay' continue # replay last sound elif state == 'replay': play_sample(''.join(buffers)) state = 'wait'
Usage: Just make a sound… and it will replay just after.