Sound only plays once in tcl/tk (snack, pulseaudio, Linux) - linux

Question

I'm using snack package in Linux Mint 13 (Maya), tk8.5 (wish).
My audio output is an analog stereo with pulseaudio software.
Acording to this: http://www.speech.kth.se/snack/tutorial.html
all I have to do to play a sound again is to use play command again.
I have a sound object and it only plays once no matter how many times I call the play command.
I tried putting a stop command before play, like this:
mysound stop
mysound play
What happens: it plays on the first but not on the second call, plays on the third but not on the fourth call, and it goes on. This is asynchronous, which means I pushed buttons to repeat stop-play. Now, this script:
package require snack
snack::sound s
s read knock.wav
after 1000 {s play}; #play sound effect
after 5000 {s play}; #this one doesn't work
after 10000 {s play}; #this one doesn't work
after 15000 {s stop; s play}; #played
after 20000 {s stop; s play}; #not played
after 25000 {s stop; s play}; #played
Same behavior as I had using button release events. In Android, the behavior work exactly as in theory, except that it has huge delays depending on the device (e.g. the sound comes after 2 seconds in one phone and after 200ms in another with better hardware).
I know the theory is right, and my final question is: how can I improve a Linux implementation that uses a more robust sound playing? Maybe using midi sounds. A solution that could work in any UNIX machine. Does snack provide that?
Thank you so much, for this is very important for me and I believe for other as well!

Answer 1

Unfortunately you don't tell us what your system is (what linux are you using and what is your audio system and device) or what you are really doing. So please provide a minimal working example.
Here is mine, that is working interactively (I routinely use Tkcon for this).
package require sound
snack::sound s1 -load longrunning-audio.wav
s1 play
# wait
s1 stop
s1 play
s1 pause
s1 pause; # resumes playing
I use the sound package instead of snack, because we don't need the graphical elements here.
And as a script
#!/usr/bin/env tclsh
package require sound
snack::sound s1 -load longrunning-audio.wav
puts "play"; s1 play
after 4000 puts "stop" \; s1 stop
after 6000 puts "play" \; s1 play
after 10000 puts "pause" \; s1 pause
after 12000 puts "resume" \; s1 pause;
after 16000 {apply {{} {
puts "stop and exit"
s1 stop
exit
}}}
# start the event loop
vwait forever
after starts a command after the given time in microseconds. In a real program you would use some procedures for this, here it is only to simulate some interaction.
Maybe you are suffering from a badly packaged snack or your audio system is playing fools with you. I remember a similar problem with some version of pulseaudio in combination with one of the output devices. Only the start of the sound was played but the audio system stayed active (use snack::audio active to show the current state).

Answer 2

Wow, you've got a lot of callback scripts scheduled at the same time! The after calls themselves take very little time. This means that you've got several calls to s play happening at virtually the same time. You are aware that only the last such one will have any effect? It's effectively as if you did this (in the “1000ms from now” timeslot):
s play
s play
s stop; s play
s stop; s play
s stop; s play
Yes, they're several callbacks, but they'll all actually get evaluated one after each other. You won't see any time between them.
I believe that the sound object, s, can only ever be playing or not playing. Also, sounds don't play instantly (obviously) so you've got to allow time from starting the playing to stopping it if you want the sound to be heard. Doing what you're doing will result in lots of activity at the command processing level, but not so much will be observable.