/****************************************************************************
* Main decoding loop. This is where mad is used. *
****************************************************************************/
#define INPUT_BUFFER_SIZE (5*8192)
#define OUTPUT_BUFFER_SIZE 8192 /* Must be an integer multiple of 4. */
static int MpegAudioDecoder(FILE *InputFp, FILE *OutputFp)
{
struct mad_stream Stream;
struct mad_frame Frame;
struct mad_synth Synth;
mad_timer_t Timer;
unsigned char InputBuffer[INPUT_BUFFER_SIZE+MAD_BUFFER_GUARD],
OutputBuffer[OUTPUT_BUFFER_SIZE],
*OutputPtr=OutputBuffer,
*GuardPtr=NULL;
const unsigned char *OutputBufferEnd=OutputBuffer+OUTPUT_BUFFER_SIZE;
int Status=0,
i;
unsigned long FrameCount=0;
bstdfile_t *BstdFile;
/* First the structures used by libmad must be initialized. */
mad_stream_init(&Stream);
mad_frame_init(&Frame);
mad_synth_init(&Synth);
mad_timer_reset(&Timer);
/* Decoding options can here be set in the options field of the
* Stream structure.
*/
/* {1} When decoding from a file we need to know when the end of
* the file is reached at the same time as the last bytes are read
* (see also the comment marked {3} bellow). Neither the standard
* C fread() function nor the POSIX read() system call provides
* this feature. We thus need to perform our reads through an
* interface having this feature, this is implemented here by the
* bstdfile.c module.
*/
BstdFile=NewBstdFile(InputFp);
if(BstdFile==NULL)
{
fprintf(stderr,"%s: can't create a new bstdfile_t (%s).\n",
ProgName,strerror(errno));
return(1);
}
/* This is the decoding loop. */
do
{
/* The input bucket must be filled if it becomes empty or if
* it's the first execution of the loop.
*/
if(Stream.buffer==NULL || Stream.error==MAD_ERROR_BUFLEN)
{
size_t ReadSize,
Remaining;
unsigned char *ReadStart;
/* {2} libmad may not consume all bytes of the input
* buffer. If the last frame in the buffer is not wholly
* contained by it, then that frame's start is pointed by
* the next_frame member of the Stream structure. This
* common situation occurs when mad_frame_decode() fails,
* sets the stream error code to MAD_ERROR_BUFLEN, and
* sets the next_frame pointer to a non NULL value. (See
* also the comment marked {4} bellow.)
*
* When this occurs, the remaining unused bytes must be
* put back at the beginning of the buffer and taken in
* account before refilling the buffer. This means that
* the input buffer must be large enough to hold a whole
* frame at the highest observable bit-rate (currently 448
* kb/s). XXX=XXX Is 2016 bytes the size of the largest
* frame? (448000*(1152/32000))/8
*/
if(Stream.next_frame!=NULL)
{
Remaining=Stream.bufend-Stream.next_frame;
memmove(InputBuffer,Stream.next_frame,Remaining);
ReadStart=InputBuffer+Remaining;
ReadSize=INPUT_BUFFER_SIZE-Remaining;
}
else
ReadSize=INPUT_BUFFER_SIZE,
ReadStart=InputBuffer,
Remaining=0;
/* Fill-in the buffer. If an error occurs print a message
* and leave the decoding loop. If the end of stream is
* reached we also leave the loop but the return status is
* left untouched.
*/
ReadSize=BstdRead(ReadStart,1,ReadSize,BstdFile);
if(ReadSize<=0)
{
if(ferror(InputFp))
{
fprintf(stderr,"%s: read error on bit-stream (%s)\n",
ProgName,strerror(errno));
Status=1;
}
if(feof(InputFp))
fprintf(stderr,"%s: end of input stream\n",ProgName);
break;
}
/* {3} When decoding the last frame of a file, it must be
* followed by MAD_BUFFER_GUARD zero bytes if one wants to
* decode that last frame. When the end of file is
* detected we append that quantity of bytes at the end of
* the available data. Note that the buffer can't overflow
* as the guard size was allocated but not used the the
* buffer management code. (See also the comment marked
* {1}.)
*
* In a message to the mad-dev mailing list on May 29th,
* 2001, Rob Leslie explains the guard zone as follows:
*
* "The reason for MAD_BUFFER_GUARD has to do with the
* way decoding is performed. In Layer III, Huffman
* decoding may inadvertently read a few bytes beyond
* the end of the buffer in the case of certain invalid
* input. This is not detected until after the fact. To
* prevent this from causing problems, and also to
* ensure the next frame's main_data_begin pointer is
* always accessible, MAD requires MAD_BUFFER_GUARD
* (currently 8) bytes to be present in the buffer past
* the end of the current frame in order to decode the
* frame."
*/
if(BstdFileEofP(BstdFile))
{
GuardPtr=ReadStart+ReadSize;
memset(GuardPtr,0,MAD_BUFFER_GUARD);
ReadSize+=MAD_BUFFER_GUARD;
}
/* Pipe the new buffer content to libmad's stream decoder
* facility.
*/
mad_stream_buffer(&Stream,InputBuffer,ReadSize+Remaining);
Stream.error=0;
}
/* Decode the next MPEG frame. The streams is read from the
* buffer, its constituents are break down and stored the the
* Frame structure, ready for examination/alteration or PCM
* synthesis. Decoding options are carried in the Frame
* structure from the Stream structure.
*
* Error handling: mad_frame_decode() returns a non zero value
* when an error occurs. The error condition can be checked in
* the error member of the Stream structure. A mad error is
* recoverable or fatal, the error status is checked with the
* MAD_RECOVERABLE macro.
*
* {4} When a fatal error is encountered all decoding
* activities shall be stopped, except when a MAD_ERROR_BUFLEN
* is signaled. This condition means that the
* mad_frame_decode() function needs more input to complete
* its work. One shall refill the buffer and repeat the
* mad_frame_decode() call. Some bytes may be left unused at
* the end of the buffer if those bytes forms an incomplete
* frame. Before refilling, the remaining bytes must be moved
* to the beginning of the buffer and used for input for the
* next mad_frame_decode() invocation. (See the comments
* marked {2} earlier for more details.)
*
* Recoverable errors are caused by malformed bit-streams, in
* this case one can call again mad_frame_decode() in order to
* skip the faulty part and re-sync to the next frame.
*/
if(mad_frame_decode(&Frame,&Stream))
{
if(MAD_RECOVERABLE(Stream.error))
{
/* Do not print a message if the error is a loss of
* synchronization and this loss is due to the end of
* stream guard bytes. (See the comments marked {3}
* supra for more informations about guard bytes.)
*/
if(Stream.error!=MAD_ERROR_LOSTSYNC ||
Stream.this_frame!=GuardPtr)
{
fprintf(stderr,"%s: recoverable frame level error (%s)\n",
ProgName,MadErrorString(&Stream));
fflush(stderr);
}
continue;
}
else
if(Stream.error==MAD_ERROR_BUFLEN)
continue;
else
{
fprintf(stderr,"%s: unrecoverable frame level error (%s).\n",
ProgName,MadErrorString(&Stream));
Status=1;
break;
}
}
/* The characteristics of the stream's first frame is printed
* on stderr. The first frame is representative of the entire
* stream.
*/
if(FrameCount==0)
if(PrintFrameInfo(stderr,&Frame.header))
{
Status=1;
break;
}
/* Accounting. The computed frame duration is in the frame
* header structure. It is expressed as a fixed point number
* whole data type is mad_timer_t. It is different from the
* samples fixed point format and unlike it, it can't directly
* be added or subtracted. The timer module provides several
* functions to operate on such numbers. Be careful there, as
* some functions of libmad's timer module receive some of
* their mad_timer_t arguments by value!
*/
FrameCount++;
mad_timer_add(&Timer,Frame.header.duration);
/* Between the frame decoding and samples synthesis we can
* perform some operations on the audio data. We do this only
* if some processing was required. Detailed explanations are
* given in the ApplyFilter() function.
*/
if(DoFilter)
ApplyFilter(&Frame);
/* Once decoded the frame is synthesized to PCM samples. No errors
* are reported by mad_synth_frame();
*/
mad_synth_frame(&Synth,&Frame);
/* Synthesized samples must be converted from libmad's fixed
* point number to the consumer format. Here we use unsigned
* 16 bit big endian integers on two channels. Integer samples
* are temporarily stored in a buffer that is flushed when
* full.
*/
for(i=0;i<Synth.pcm.length;i++)
{
signed short Sample;
/* Left channel */
Sample=MadFixedToSshort(Synth.pcm.samples[0][i]);
*(OutputPtr++)=Sample>>8;
*(OutputPtr++)=Sample&0xff;
/* Right channel. If the decoded stream is monophonic then
* the right output channel is the same as the left one.
*/
if(MAD_NCHANNELS(&Frame.header)==2)
Sample=MadFixedToSshort(Synth.pcm.samples[1][i]);
*(OutputPtr++)=Sample>>8;
*(OutputPtr++)=Sample&0xff;
/* Flush the output buffer if it is full. */
if(OutputPtr==OutputBufferEnd)
{
if(fwrite(OutputBuffer,1,OUTPUT_BUFFER_SIZE,OutputFp)!=OUTPUT_BUFFER_SIZE)
{
fprintf(stderr,"%s: PCM write error (%s).\n",
ProgName,strerror(errno));
Status=2;
break;
}
OutputPtr=OutputBuffer;
}
}
}while(1);
/* The input file was completely read; the memory allocated by our
* reading module must be reclaimed.
*/
BstdFileDestroy(BstdFile);
/* Mad is no longer used, the structures that were initialized must
* now be cleared.
*/
mad_synth_finish(&Synth);
mad_frame_finish(&Frame);
mad_stream_finish(&Stream);
/* If the output buffer is not empty and no error occurred during
* the last write, then flush it.
*/
if(OutputPtr!=OutputBuffer && Status!=2)
{
size_t BufferSize=OutputPtr-OutputBuffer;
if(fwrite(OutputBuffer,1,BufferSize,OutputFp)!=BufferSize)
{
fprintf(stderr,"%s: PCM write error (%s).\n",
ProgName,strerror(errno));
Status=2;
}
}
/* Accounting report if no error occurred. */
if(!Status)
{
char Buffer[80];
/* The duration timer is converted to a human readable string
* with the versatile, but still constrained mad_timer_string()
* function, in a fashion not unlike strftime(). The main
* difference is that the timer is broken into several
* values according some of it's arguments. The units and
* fracunits arguments specify the intended conversion to be
* executed.
*
* The conversion unit (MAD_UNIT_MINUTES in our example) also
* specify the order and kind of conversion specifications
* that can be used in the format string.
*
* It is best to examine libmad's timer.c source-code for details
* of the available units, fraction of units, their meanings,
* the format arguments, etc.
*/
mad_timer_string(Timer,Buffer,"%lu:%02lu.%03u",
MAD_UNITS_MINUTES,MAD_UNITS_MILLISECONDS,0);
fprintf(stderr,"%s: %lu frames decoded (%s).\n",
ProgName,FrameCount,Buffer);
}
/* That's the end of the world (in the H. G. Wells way). */
return(Status);
}
madx_sig madx_read ( unsigned char *in_buffer,
unsigned char *out_buffer, madx_house *mxhouse, madx_stat *mxstat)
{
// "Random" seed for generating dither. Used
// by scale_audio() in preparing the samples
// for 16 bit output.
mad_fixed_t rnscale = 0xa8b9ff7e;
unsigned char *guard_ptr = NULL;
unsigned char *readstart;
// Clear mxstat->msg
sprintf(mxstat->msg,"");
mxstat->buffstart = 0;
// Input file has been read completely
if ( mxstat->is_eof && !mxstat->readsize )
{
sprintf(mxstat->msg,"End of input stream");
return(EOF_REACHED);
}
// Executes on initial loop
if ( (mxstat->readsize == 0) &&
(mxstat->remaining == 0) &&
mxhouse->stream.buffer == NULL )
{
mxstat->readsize = MADX_INPUT_BUFFER_SIZE;
mxstat->remaining = 0;
return(MORE_INPUT);
}
readstart = in_buffer;
// Stream buffer
if ( mxhouse->stream.buffer == NULL ||
mxhouse->stream.error == MAD_ERROR_BUFLEN )
{
// BUFFER_GUARD
// "mxstat->is_eof" must be set to
// non-zero IMMEDIATELY (see "test.cpp")
// once it is detected, so the following
// may execute, padding the buffer.
if( mxstat->is_eof )
{
guard_ptr = in_buffer + mxstat->readsize;
memset( guard_ptr, 0, MAD_BUFFER_GUARD );
mxstat->readsize += MAD_BUFFER_GUARD;
}
// Pipe the new buffer content to libmad's
// stream decoder facility.
mad_stream_buffer( &mxhouse->stream,
in_buffer, mxstat->readsize + mxstat->remaining );
mxhouse->stream.error = (mad_error)0;
}
// [Madlld comment]:
// Decode the next MPEG frame. The streams is read from the
// buffer, its constituents are broken down and stored in the
// mxhouse->frame structure, ready for examination/alteration
// or PCM synthesis. Decoding options are carried in the Frame
// structure from the mxhouse->stream structure.
//
// Error handling: mad_frame_decode() returns a non zero value
// when an error occurs. The error condition can be checked in
// the error member of the mxhouse->stream structure. A mad error is
// recoverable or fatal, the error status is checked with the
// MAD_RECOVERABLE macro.
//
// {4} When a fatal error is encountered all decoding
// activities shall be stopped, except when a MAD_ERROR_BUFLEN
// is signaled. This condition means that the
// mad_frame_decode() function needs more input to complete
// its work. One shall refill the buffer and repeat the
// mad_frame_decode() call. Some bytes may be left unused at
// the end of the buffer if those bytes forms an incomplete
// frame. Before refilling, the remaining bytes must be moved
// to the beginning of the buffer and used for input for the
// next mad_frame_decode() invocation. (See the comments
// marked {2} earlier for more details.)
//
// Recoverable errors are caused by malformed bit-streams, in
// this case one can call again mad_frame_decode() in order to
// skip the faulty part and re-sync to the next frame.
if( mad_frame_decode(&mxhouse->frame, &mxhouse->stream) )
{
if( MAD_RECOVERABLE(mxhouse->stream.error) )
{
// Do not print a message if the error is
// a loss of synchronization or this loss
// is due to the end of stream guard bytes.
if( mxhouse->stream.error != MAD_ERROR_LOSTSYNC
||
mxhouse->stream.this_frame != guard_ptr
||
// Suppress error if caused by ID3 tag.
(mxhouse->stream.this_frame[0] != 'I' && // ID3v2
mxhouse->stream.this_frame[1] != 'D' &&
mxhouse->stream.this_frame[2] != '3')
||
(mxhouse->stream.this_frame[0] != 'T' && // ID3v1
mxhouse->stream.this_frame[1] != 'A' &&
mxhouse->stream.this_frame[2] != 'G') )
{
sprintf(mxstat->msg,"Recoverable frame level error (%s)",
MadErrorString(&mxhouse->stream));
}
return(CALL_AGAIN);
}
else // Non-recoverable error
{
// MAD_ERROR_BUFLEN means that more input
// is needed (it's not recoverable without
// interaction from the calling code). The
// bytes already in the buffer must be
// preserved. "mxstat->buffstart" is used
// to point to the end of the preserved
// bytes in "in_buffer", then MORE_INPUT
// is requested. "mxstat->buffstart" is set
// to 0 every time "madx_read()" is
// called. The calling code checks this
// variable to determine if a full buffer
// read or a partial read is necessary.
// (Not "0" signifies a partial read.)
if( mxhouse->stream.error == MAD_ERROR_BUFLEN )
{
sprintf(mxstat->msg,
"Need more input (%s)", MadErrorString(&mxhouse->stream));
mxstat->remaining =
mxhouse->stream.bufend - mxhouse->stream.next_frame;
memmove(in_buffer,
mxhouse->stream.next_frame, mxstat->remaining);
mxstat->readsize = MADX_INPUT_BUFFER_SIZE - mxstat->remaining;
// How far "forward" in_buffer to begin:
mxstat->buffstart = in_buffer + mxstat->remaining;
return(MORE_INPUT);
}
else // Error returned
{
sprintf(mxstat->msg,"Unrecoverable frame level error (%s).",
MadErrorString(&mxhouse->stream));
return(ERROR_OCCURED);
}
}
}
// [Madlld comment]:
// Accounting. The computed frame duration is in the frame
// header structure. It is expressed as a fixed point number
// whole data type is mad_timer_t. It is different from the
// samples fixed point format and unlike it, it can't directly
// be added or subtracted. The timer module provides several
// functions to operate on such numbers. Be careful there, as
// some functions of libmad's timer module receive some of
// their mad_timer_t arguments by value!
mxhouse->frame_cnt++;
mad_timer_add( &mxhouse->timer, mxhouse->frame.header.duration );
// Once decoded the frame is synthesized to
// PCM samples. No errors are reported by
// mad_synth_frame();
mad_synth_frame( &mxhouse->synth, &mxhouse->frame );
// [Madlld comment]:
// Synthesized samples must be converted from libmad's fixed
// point number to the consumer format. Here we use unsigned
// 16 bit big endian integers on two channels. Integer samples
// are temporarily stored in a buffer that is flushed when
// full.
//
// Note: Code to computer "big-endian" has been preserved
// below. It is simply commented out. This source produces
// 16-bit "little-endian" PCM samples.
for( int i=0; i < mxhouse->synth.pcm.length; i++ )
{
signed short sample;
// Left channel
sample = scale_audio(mxhouse->synth.pcm.samples[0][i], &rnscale);
// Originally big-endian:
// *(mxhouse->output_ptr++)=sample>>8;
// *(mxhouse->output_ptr++)=sample&0xff;
// 16-bit little-endian
*(mxhouse->output_ptr++)=((sample>>0) & 0xff);
*(mxhouse->output_ptr++)=((sample>>8) & 0xff);
// Right channel.
// If the decoded stream is monophonic then
// the right output channel is the same as
// the left one.
if(MAD_NCHANNELS(&mxhouse->frame.header)==2)
sample = scale_audio(mxhouse->synth.pcm.samples[1][i], &rnscale);
// Originally big-endian:
// *(mxhouse->output_ptr++)=sample>>8;
// *(mxhouse->output_ptr++)=sample&0xff;
// 16-bit little-endian
*(mxhouse->output_ptr++)=((sample>>0) & 0xff);
*(mxhouse->output_ptr++)=((sample>>8) & 0xff);
}
// Tell calling code buffer size
mxstat->write_size = mxhouse->output_ptr - out_buffer;
// Indicate that buffer is ready to be
// written.
if (mxhouse->synth.pcm.length < 1152
||
MADX_OUTPUT_BUFFER_SIZE - mxstat->write_size < 1152)
{
// Reset pointer
mxhouse->output_ptr = out_buffer;
return(FLUSH_BUFFER);
}
else
return(CALL_AGAIN); // Otherwise, continue
}