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Synchronous/Asynchrnous Audio play with pymedia


I'm developing a piece of software to assist illiteraate adults to learn to
read. I'm trying to figure out how, if possible, to make audio playback
asynchrnous but still controllable. I'm using python 2.4 with pymedia on
XP. I started out with the example in the tutorials section of the pymedia
website. The pymedia docs imply to me that playback using Output's play()
method should already be asynchronous and controllable. I judge this
because of the presence of the pause() and unpause() methods. However, when
I run the example I find that play() in fact is not returning until an
entire frame has been played through the sound card. This isn't entirely a
problem since the frames are small, but I would prefer to give the entire
sound file to the class and let it go on playing while I continue with other
processing. If, at some point during playback, I wish to pause, unpause or
completely stop playback, I would like, again, to be able to make
asynchronous calls to do so. Doe anybody know if this is possible? Am I
using pymedia incorrectly?

I've attempted to construct a threaded class to handle my problem, but I'm a
novice with threads and It's not working properly. To use this class, first
make an instance. To assign an mp3 file for playback use myInst.select(
myFileObj ). To begin playback or to unpause use: myInst.play( ). to
pause use: myInst.pause( ). to stop use: myInst.stop( ). Once stopped,
myInst.play( ) should restart playback from the beginning. The problem is
that when I stop(), restarting with play() doesn't work. Instead, the
thread silently terminates.

Thanks for any help you can offer. I've been trying to solve this on my own
for days now and just know it shouldn't be this hard.

import time
import pymedia.audio.sound as sound
import pymedia.audio.acodec as acodec
import threading, Queue

class AudioPlayer( threading.Thread ):
# States
PLAY = 1
STOP = 3

def __init__( self ):
threading.Thread.__init__( self )

self.setDaemon( 1 )
self.requestQueue = Queue.Queue( )
self.start( )

def select( self, filelikeObj ):
self.requestQueue.put( filelikeObj )

def play( self ):
self.requestQueue.put( AudioPlayer.PLAY )

def pause( self ):
self.requestQueue.put( AudioPlayer.PAUSE )

def stop( self ):
self.requestQueue.put( AudioPlayer.STOP )

def run( self ):
state = AudioPlayer.STOP
file = None
snd = None

while True:
if (state == AudioPlayer.PLAY) and self.requestQueue.empty( ):
if not snd:
cparams= { 'id': acodec.getCodecID( 'mp3' ) }
codec = acodec.Decoder( cparams )
file.seek( 0 )
bytes = file.read( 8192 )
frame = codec.decode( bytes )
snd = sound.Output( frame.sample_rate, frame.channels,
sound.AFMT_S16_LE )
bytes = file.read( 512 )
if len(bytes) > 0:
frame = codec.decode( bytes )

if frame:
snd.play( frame.data )
if snd:
snd.stop( )
snd = None
state = AudioPlayer.STOP
msg = self.requestQueue.get( )

if msg in ( AudioPlayer.PAUSE, AudioPlayer.PLAY ):
state = msg
if snd:
snd.stop( )
snd = None
state = AudioPlayer.STOP
if msg != AudioPlayer.STOP:
file = msg

# Test application
if __name__ == '__main__':
import time
player = AudioPlayer( )
snd = open( 'music.mp3', 'rb' )
player.select( snd )
player.play( )
time.sleep( 3 )

player.pause( )
time.sleep( 3 )
player.play( )
time.sleep( 10 )
player.stop( )
time.sleep( 3 )
player.play( )

Sep 18 '05 #1
1 4267
At 01:22 19.09.2005, Ron Provost wrote:

I'm developing a piece of software to assist illiteraate adults to learn to
read. I'm trying to figure out how, if possible, to make audio playback
asynchrnous but still controllable. I'm using python 2.4 with pymedia on

there's a pymedia mailing list at:
better ask there, the author of pymedia is generally very helpful in
answering question.

Sep 19 '05 #2

This thread has been closed and replies have been disabled. Please start a new discussion.

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