AudioQueue basics - elapsed time and seeking
AudioQueue basics - elapsed time and seeking
- Subject: AudioQueue basics - elapsed time and seeking
- From: Alex Kac <email@hidden>
- Date: Tue, 23 Sep 2008 12:02:53 -0500
So I thought I understood everything and I thought I got it all
working perfectly. Only to find out I must not know anything and
everything I've done was an accident :(
I am using AudioQueue to play files in PCM and IMA4 format. These
sound files show up in the UI with elapsed time and a scrubbing slider.
Now there are some methods in my player class that I have written that
work perfectly in PCM format, but not IMA4. I don't understand
AudioQueue timelines yet, but the docs are so sparse I'm not even sure
they would help.
My methods:
- (Float64) duration
{
Float64 duration = 0;
UInt32 sizeOfCount = sizeof (duration);
AudioFileGetProperty (
[self audioFileID],
kAudioFilePropertyEstimatedDuration,
&sizeOfCount,
&duration
);
return duration;
}
- (Float64) secondsElapsed
{
Float64 numPacketsForTime = self.startingPacketNumber /
(audioFormat.mSampleRate * audioFormat.mFramesPerPacket);
return numPacketsForTime;
}
- (void) seekToTimeSeconds:(Float64)timeSeconds;
{
seeking = YES;
Float64 numPacketsForTime = audioFormat.mSampleRate /
audioFormat.mFramesPerPacket * timeSeconds;
self.startingPacketNumber = numPacketsForTime;
}
So we call the "secondsElapsed" method and get a time and that works
for PCM. For IMA4 I get such small numbers that it reads 0 seconds at
all times in my elapsed time string. I tried using
- (Float64) secondsElapsed
{
AudioTimeStamp t = {0};
OSStatus err = AudioQueueGetCurrentTime(self.queueObject,NULL,&t,NULL);
if (err == noErr)
return t.mSampleTime / audioFormat.mSampleRate;
return 0;
}
but that only returned the total playing time - not the elapsed time
from the position in the scrubber.
So I'm sitting here scratching my head, trying to read through the
docs and figure out what I'm missing. It all works well enough for
PCM, but not for IMA4 or anything else. I'd like to not only get help
for this, but also simply understand why.
Thanks.
--
Alex Kac
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