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Re: AudioQueue newbie : Handling Forward , Rewind , etc..,
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Re: AudioQueue newbie : Handling Forward , Rewind , etc..,

Devon and William , thanks for the valuable and timely input.
your suggestions lead to different solution , thought all the solutions are working like a charm :D ( for forward and backward features )

but I have come across some issue .......

the Structure I employed is

typedef struct {
    AudioStreamBasicDescription   mDataFormat;
    AudioQueueRef                 mQueue;
    AudioQueueBufferRef           mBuffers[kNumberBuffers];
    AudioFileID                   mAudioFile;
    UInt32                        bufferByteSize;
    SInt64                        mCurrentPacket;
    UInt32                        mNumPacketsToRead;
    AudioStreamPacketDescription  *mPacketDescs;
    bool                          mIsRunning;
}AQPlayer


-(id)init
{
aqData = malloc(sizeof(AQPlayer));
// other allocation and initialization routines for AudioQueue
AudioQueueNewOutput (&(aqData- >mDataFormat),HandleOutputBuffer,aqData,CFRunLoopGetCurrent (),kCFRunLoopCommonModes,0,&(aqData->mQueue));
//etc.,,,,

}

- (void)startPlayback
{
	AudioQueueStart (aqData->mQueue,NULL);
}

- (void)pausePlayback
{
	AudioQueuePause(aqData->mQueue);
}

- (void)playFrom:(float )seekPoint
{
UInt32 propertySize;
UInt64 totPackets;
propertySize = sizeof(totPackets);
OSStatus err = AudioFileGetProperty(aqData->mAudioFile, kAudioFilePropertyAudioDataPacketCount, &propertySize, &totPackets);
totPackets= totPackets* seekPoint ;
aqData->mCurrentPacket = totPackets;
}

static void HandleOutputBuffer (void *aqData,AudioQueueRef inAQ,AudioQueueBufferRef inBuffer)
{
AQPlayer *pAqData = (AQPlayer *) aqData;
if (pAqData->mIsRunning == 0) return;
UInt32 numBytesReadFromFile;
UInt32 numPackets = pAqData->mNumPacketsToRead;
AudioFileReadPackets (pAqData->mAudioFile, false,&numBytesReadFromFile,pAqData->mPacketDescs,pAqData- >mCurrentPacket,&numPackets,inBuffer->mAudioData);
if (numPackets > 0) {
inBuffer->mAudioDataByteSize = numBytesReadFromFile;
AudioQueueEnqueueBuffer (pAqData->mQueue,inBuffer, (pAqData- >mPacketDescs ? numPackets : 0), pAqData->mPacketDescs );
pAqData->mCurrentPacket += numPackets;
} else {
AudioQueueStop (
pAqData->mQueue,
false
);
pAqData->mIsRunning = false;
}


UInt32 propertySize = sizeof(pAqData->mDataFormat);
UInt64 numBytes;
propertySize = sizeof(numBytes);
UInt64 totPackets;
propertySize = sizeof(totPackets);
OSStatus err = AudioFileGetProperty(pAqData->mAudioFile, kAudioFilePropertyAudioDataPacketCount, &propertySize, &totPackets);
printf("numPackets ------- %d mCurrentPacket %d percentage is %f mAudioDataByteSize %d \n", totPackets,pAqData->mCurrentPacket , (pAqData->mCurrentPacket)/totPackets ,inBuffer->mAudioDataByteSize );
NSTimeInterval seconds;
propertySize = sizeof(seconds);
err = AudioFileGetProperty(pAqData->mAudioFile, kAudioFilePropertyEstimatedDuration, &propertySize, &seconds);
printf("seconds %f \n",seconds);
}



The issue is :
o/p is numPackets ------- 7444 mCurrentPacket 0 percentage is 0.000000 mAudioDataByteSize 0 seconds 194.455510

1) currentPacket is always "zero" no matter what I do...... hence I cant get percentage played. Hence showing the percentage played has to be calculated in reverse way.... ( but its working so far ) I think I have to maintain separate index for maintaining the packet Index ( as suggested by Devon )

2) and also observe that , the Estimated Time differs to the actual time by a 'mile' to be precise by 7 sec.
Is there a way to get the actual duration of file ??

am I missing any obvious part in it ? :)

Once again thank you guys.



On Jul 30, 2008, at 1:27 AM, William Stewart wrote:

On Jul 29, 2008, at 12:22 PM, Devon Tucker wrote:

Raj,

I'm currently grappling with the exact same issues. I think I know how to solve these problems conceptually but I'm not sure about the implementation. Keep in mind that I know very little about digital audio so I hope someone will correct me if I'm wrong (Which I very well could be).

For forward and rewind, seeking, you need to determine the packet index given the time in seconds you wish to seek to. For example given that you want to seek to time "pos" you would calculate the necessary packet index like this:

packetIndex = (pos * sampleRate) / framesPerPacket

Implementation-wise, I guess, depends on how you want to do it. You could stop playback, clear your buffers, start buffering from then new packet index and start playback again. You could also simply reset your packetIndex to the desired index and keep playing normally.

Yes - that's pretty much it. You can implement a skip-type fast forward by just feeding in bits of data as you skip through the file.

As for tracking the position through the song, this can be accomplished much the same way. Given the currently playing packet we can determine the position by:

AudioQueueGetCurrentTime

An audio queue always starts at sample time == 0.

position = (packetIndex * framesPerPacket) / sampleRate

In order to keep track of the position in the audio file, with respect to implementation, we need to keep track of our current packet index. This packet index could be different from the packet index needed for your buffer callback however, due to buffer priming. I recommend keeping a separate packet index for playback, which starts at zero when playback starts and gets incremented by the number of packets read in your buffer callback.

Hope this helps,
Devon

On 28-Jul-08, at 5:56 AM, Rajeswar Rao wrote:

Hi ,

Im trying to paly audio file, using AudioQueue ,
I could Play , Pause using AudioQueueStart and AudioQueuePause ;

Now im trying to implement 'Forward/Rewind' functionality also the duration played so far .....
How can I achieve this ? Do I have to handle these things in "Callback function" ? if so , how ?

any suggestions are appreciated.

Thanks in Adavance
~Raj
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Cheers,
Devon








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