flac dev - Sep 2004 - FLAC++ SeekableStream write_callback not being called?

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Hi,

I am trying to create a FLAC plugin for the K3b CD burning program. To do this 
I have subclassed the FLAC::Decoder::SeekableStream class. I can obtain the 
vorbiscomment data using set_metadata_respond, process_until_end_of_metadata 
and the metadata_callback, however I cannot decode the audio data. It seems 
to me as though the write_callback is never actually being called.

Before I pepper my code with a bazillion trace statements, can anyone tell me 
if there is some obvious "trick-for-new-players" which I might have
missed?

My write_callback looks like:

::FLAC__StreamDecoderWriteStatus 
K3bFLACDecoder::Private::write_callback(const ::FLAC__Frame *frame, const 
FLAC__int32 * const buffer[]) {
  int i;
  // Note that in canDecode we made sure that the input is only 16 bit stereo.
  int samples = frame->header.blocksize;

  internalBuffer = new QBuffer();
  internalBuffer->open(IO_ReadWrite);
  for(i=0; i < samples; i++) {
    internalBuffer->putch(buffer[i][0] >> 8); // msb left
    internalBuffer->putch(buffer[i][0] & 0xFF); // lsb left
    internalBuffer->putch(buffer[i][1] >> 8); // msb right
    internalBuffer->putch(buffer[i][1] & 0xFF); // lsb right
  }

  // Rewind the buffer so the decode method will take data from the beginning.
  internalBuffer->at(0);
  
  return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
}

And the code which I expect to have call it is (where "d" is an
instance of my
K3bFLACDecoder::Private class) :

  if(d->internalBuffer == 0) {
    if(d->get_state() == FLAC__SEEKABLE_STREAM_DECODER_END_OF_STREAM) {
      // Nothing left to do.
      return 0;
    } else {
      // Get some more data into our internal buffer.
      d->process_single();
    }
  }

Yet my internalBuffer is never initialised. I have also tried to have:

 while(d->internalBuffer==0)
   d->process_single();

but this only results in an infinite loop. I get similarly depressing results 
from process_until_end_of_stream.

Any suggestions would be appreciated.

cheers,

John
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I'll have to see the whole class definition to tell what's
wrong; nothing below looks wrong.

the unit tests (see src/test_libFLAC++/) have some examples
and the write callbacks do get called.

Josh

--- John Steele Scott <toojays@toojays.net> wrote:
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> Hash: SHA1
> 
> Hi,
> 
> I am trying to create a FLAC plugin for the K3b CD burning program.
> To do this 
> I have subclassed the FLAC::Decoder::SeekableStream class. I can
> obtain the 
> vorbiscomment data using set_metadata_respond,
> process_until_end_of_metadata 
> and the metadata_callback, however I cannot decode the audio data. It
> seems 
> to me as though the write_callback is never actually being called.
> 
> Before I pepper my code with a bazillion trace statements, can anyone
> tell me 
> if there is some obvious "trick-for-new-players" which I might
have
> missed?
> 
> My write_callback looks like:
> 
> ::FLAC__StreamDecoderWriteStatus 
> K3bFLACDecoder::Private::write_callback(const ::FLAC__Frame *frame,
> const 
> FLAC__int32 * const buffer[]) {
>   int i;
>   // Note that in canDecode we made sure that the input is only 16
> bit stereo.
>   int samples = frame->header.blocksize;
> 
>   internalBuffer = new QBuffer();
>   internalBuffer->open(IO_ReadWrite);
>   for(i=0; i < samples; i++) {
>     internalBuffer->putch(buffer[i][0] >> 8); // msb left
>     internalBuffer->putch(buffer[i][0] & 0xFF); // lsb left
>     internalBuffer->putch(buffer[i][1] >> 8); // msb right
>     internalBuffer->putch(buffer[i][1] & 0xFF); // lsb right
>   }
> 
>   // Rewind the buffer so the decode method will take data from the
> beginning.
>   internalBuffer->at(0);
>   
>   return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
> }
> 
> And the code which I expect to have call it is (where "d" is an
> instance of my 
> K3bFLACDecoder::Private class) :
> 
>   if(d->internalBuffer == 0) {
>     if(d->get_state() == FLAC__SEEKABLE_STREAM_DECODER_END_OF_STREAM)
> {
>       // Nothing left to do.
>       return 0;
>     } else {
>       // Get some more data into our internal buffer.
>       d->process_single();
>     }
>   }
> 
> Yet my internalBuffer is never initialised. I have also tried to
> have:
> 
>  while(d->internalBuffer==0)
>    d->process_single();
> 
> but this only results in an infinite loop. I get similarly depressing
> results 
> from process_until_end_of_stream.
> 
> Any suggestions would be appreciated.
> 
> cheers,
> 
> John
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On Thu, 27 Nov 2003 04:59, you wrote:
> I'll have to see the whole class definition to tell what's
> wrong; nothing below looks wrong.
>
> the unit tests (see src/test_libFLAC++/) have some examples
> and the write callbacks do get called.
Josh,

Thanks for your reply. It turns out that the problem was due to finish() 
inadvertently being called on the stream prior to process_single(). It works 
fine now.

cheers,

John
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