Archived:MaoscPlayCompete() callback not received after output stream underflow (Known Issue)

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When using CMdaAudioOutputStream, MaoscPlayCompete() callback is not received automatically after all the buffers have been sent to server side and played back.

Article Metadata

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Compatibility

Platform(s): S60 2nd Edition and FP1, FP2, FP3
S60 3rd Edition (initial release) and FP1

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Article

Created: User:Technical writer 1 (16 Apr 2007)

Last edited: hamishwillee (21 Jun 2012)

Description

CMdaAudioOutputStream uses callbacks (MMdaAudioOutputStreamCallback) to notify the client of the playback progress. According to SDK documentation, MaoscPlayComplete() callback is received when all descriptors have been sent.

However, MaoscPlayComplete() callback is received only after an explicit call to CMdaAudioOutputStream::Stop(), not after the all the buffers have been processed and the output stream has underflowed.

Solution

After the output stream underflows, it will continue to wait for new buffers. At this point, the only way of releasing the stream is to call CMdaAudioOutputStream::Stop().

Since no notification about the underflow is received, the client will need some mechanism to determine when to stop the stream. Specifically, the client needs to know which buffer will be the last one to be played back. When (a pointer to) the last buffer is known, it is possible to detect when it has been copied to server side in MaoscBufferCopied, and then proceed to stop the stream.

On S60 2nd Edition devices, a call to CMdaAudioOutputStream::Stop() should not be made directly inside MaoscBufferCopied(), as it may result in a panic. Instead, the client can start a low-priority active object (CIdle), which will then call Stop() once it completes.

The following code demonstrates stopping the output stream with an active object:

    void CAudioStreamEngine::ConstructL()
        {
        ...
        // Construct the active object (CIdle) used for stopping the stream
        iStop = CIdle::NewL( EPriorityIdle );
        }
 
    void CAudioStreamEngine::MaoscBufferCopied( TInt aError, const TDesC8& aBuffer )
        {
        if( aError == KErrNone )
            {
            // Compare the copied buffer to the known last buffer
            if( &aBuffer == iLastBuffer )
                {
                // Playback is complete:
                // Start the active object that will stop the stream
                iStop->Start( TCallBack(BackgroundStop, this) );
                return;
                }
            // Write the next playback buffer to the stream
            else
                {
                iOutputStream->WriteL( GetNextBuffer() );
                }    
            }
        else
            {
            // Error handling
            }   
        }
 
 
    TInt CAudioStreamEngine::BackgroundStop( TAny *aStream )  // static member function
        {
        return ((CAudioStreamEngine*)aStream)->Stop();
        }
 
    TBool CAudioStreamEngine::Stop()
        {
        iOutputStream->Stop();  // will result in MaoscPlayComplete() call
        return EFalse;
        }

Note: On S60 3rd Edition, CMdaAudioOutputStream::Stop() can also be called from within MaoscBufferCopied().