C++ MAD_RECOVERABLE函数代码示例

static int mp3_decode_frame (mp3_s *mp3)
{
  if (mp3->stream.buffer == NULL || mp3->stream.error == MAD_ERROR_BUFLEN) {
    if (mp3_fill_input (mp3) < 0) {
      return DECODE_BREAK;
    }
  }

  if (mad_frame_decode (&mp3->frame, &mp3->stream)) {
    if (MAD_RECOVERABLE (mp3->stream.error)) {
      return DECODE_CONT;
    } else {
      if (mp3->stream.error == MAD_ERROR_BUFLEN) {
	return DECODE_CONT;
      } else {
	printf ("Unrecoverable frame error: \'%s\'\n", mad_stream_errorstr (&mp3->stream));
	mp3->status = 1;
	return DECODE_BREAK;
      }
    }
  }

  mp3->frame_count++;

  return DECODE_OK;
}

    //
    // Read up samples from madSynth_
    // If needed, read some more MP3 data, decode them and synth them
    // Place in audioBuffer_.
    // Return number of samples read.
    //
    size_t MadDecoder::decode(size_t numPendingTotal, AudioBuffer* buffer)
    {
        size_t numProcessedTotal = 0;
        int numChannels = getNumChannels();
        mad_fixed_t sample;

        do {
            size_t numPendingFrame = (madSynth_.pcm.length - currentFrame_) * numChannels;
            numPendingFrame = std::min(numPendingTotal, numPendingFrame);
            size_t numProcessedFrame = 0;

            while (numProcessedFrame < numPendingFrame)
            {
                for (int channel = 0; channel < numChannels; channel++)
                {
                    sample = madSynth_.pcm.samples[channel][currentFrame_];
                    if (sample < -MAD_F_ONE)
                        sample = -MAD_F_ONE;
                    else if (sample >= MAD_F_ONE)
                        sample = MAD_F_ONE - 1;

                    float fSample = (float)(sample / (float)(1L << MAD_F_FRACBITS));
                    float* pos = buffer->getHead() + numProcessedTotal;
                    *pos = fSample;
                    numProcessedFrame++;
                    numProcessedTotal++;
                }
                currentFrame_++;
            }

            numPendingTotal -= numProcessedFrame;
            if (numPendingTotal == 0)
                break;

            if (madStream_.error == MAD_ERROR_BUFLEN) {     // check whether input buffer needs a refill 
                if (readMpgFile() == false)                  // eof
                    break;
            }

            if (mad_frame_decode(&madFrame_, &madStream_))
            {
                if (MAD_RECOVERABLE(madStream_.error)) {
                    consumeId3Tag();
                    continue;
                }
                else  {
                    if (madStream_.error == MAD_ERROR_BUFLEN)
                        continue;
                    else
                        THROW(std::exception, "unrecoverable frame level error (%s).", mad_stream_errorstr(&madStream_));
                }
            }
            mad_timer_add(&madTimer_, madFrame_.header.duration);
            mad_synth_frame(&madSynth_, &madFrame_);
            currentFrame_ = 0;
            numMpegFrames_++;
        } while (true);

        return numProcessedTotal;
    }

int TrackDuration::duration(const QFileInfo &fileinfo)
{
    QString fn = fileinfo.absoluteFilePath();
    if (fn.isEmpty())
        return 0;

    QFile file(fn);
    if (!file.open(QFile::ReadOnly))
        return 0;

    mad_stream infostream;
    mad_header infoheader;
    mad_timer_t infotimer;
    mad_stream_init(&infostream);
    mad_header_init(&infoheader);
    mad_timer_reset(&infotimer);

    qint64 r;
    qint64 l = 0;
    unsigned char* buf = new unsigned char[INPUT_BUFFER_SIZE];

    while (!file.atEnd()) {
        if (l < INPUT_BUFFER_SIZE) {
            r = file.read(reinterpret_cast<char*>(buf) + l, INPUT_BUFFER_SIZE - l);
            l += r;
        }
        mad_stream_buffer(&infostream, buf, l);
        for (;;) {
            if (mad_header_decode(&infoheader, &infostream)) {
                if (!MAD_RECOVERABLE(infostream.error))
                    break;
                if (infostream.error == MAD_ERROR_LOSTSYNC) {
                    TagLib::ID3v2::Header header;
                    uint size = (uint)(infostream.bufend - infostream.this_frame);
                    if (size >= header.size()) {
                        header.setData(TagLib::ByteVector(reinterpret_cast<const char*>(infostream.this_frame), size));
                        uint tagsize = header.tagSize();
                        if (tagsize > 0) {
                            mad_stream_skip(&infostream, qMin(tagsize, size));
                            continue;
                        }
                    }
                }
                qDebug() << "header decode error while getting file info" << infostream.error;
                continue;
            }
            mad_timer_add(&infotimer, infoheader.duration);
        }
        if (infostream.error != MAD_ERROR_BUFLEN && infostream.error != MAD_ERROR_BUFPTR)
            break;
        memmove(buf, infostream.next_frame, &(buf[l]) - infostream.next_frame);
        l -= (infostream.next_frame - buf);
    }

    mad_stream_finish(&infostream);
    mad_header_finish(&infoheader);
    delete[] buf;

    return timerToMs(&infotimer);
}

void MP3Stream::readHeader() {
	if (_state != MP3_STATE_READY)
		return;

	// If necessary, load more data into the stream decoder
	if (_stream.error == MAD_ERROR_BUFLEN)
		readMP3Data();

	while (_state != MP3_STATE_EOS) {
		_stream.error = MAD_ERROR_NONE;

		// Decode the next header. Note: mad_frame_decode would do this for us, too.
		// However, for seeking we don't want to decode the full frame (else it would
		// be far too slow). Hence we perform this explicitly in a separate step.
		if (mad_header_decode(&_frame.header, &_stream) == -1) {
			if (_stream.error == MAD_ERROR_BUFLEN) {
				readMP3Data();  // Read more data
				continue;
			} else if (MAD_RECOVERABLE(_stream.error)) {
				//status("MP3Stream: Recoverable error in mad_header_decode (%s)", mad_stream_errorstr(&_stream));
				continue;
			} else {
				warning("MP3Stream: Unrecoverable error in mad_header_decode (%s)", mad_stream_errorstr(&_stream));
				break;
			}
		}

		// Sum up the total playback time so far
		mad_timer_add(&_totalTime, _frame.header.duration);
		break;
	}

	if (_stream.error != MAD_ERROR_NONE)
		_state = MP3_STATE_EOS;
}

// Seek in the stream, finding the next valid header
void Mp3PspStream::findValidHeader() {
	DEBUG_ENTER_FUNC();

	if (_state != MP3_STATE_READY)
		return;

	// If necessary, load more data into the stream decoder
	if (_stream.error == MAD_ERROR_BUFLEN)
		readMP3DataIntoBuffer();

	while (_state != MP3_STATE_EOS) {
		_stream.error = MAD_ERROR_NONE;

		// Decode the next header.
		if (mad_header_decode(&_header, &_stream) == -1) {
			if (_stream.error == MAD_ERROR_BUFLEN) {
				readMP3DataIntoBuffer();  // Read more data
				continue;
			} else if (MAD_RECOVERABLE(_stream.error)) {
				debug(6, "MP3PSPStream: Recoverable error in mad_header_decode (%s)", mad_stream_errorstr(&_stream));
				continue;
			} else {
				warning("MP3PSPStream: Unrecoverable error in mad_header_decode (%s)", mad_stream_errorstr(&_stream));
				break;
			}
		}

		// Sum up the total playback time so far
		mad_timer_add(&_totalTime, _header.duration);
		break;
	}

	if (_stream.error != MAD_ERROR_NONE)
		_state = MP3_STATE_EOS;
}

static enum mp3_action
decode_next_frame_header(struct mp3_data *data, G_GNUC_UNUSED struct tag **tag)
{
	enum mad_layer layer;

	if ((data->stream).buffer == NULL
	    || (data->stream).error == MAD_ERROR_BUFLEN) {
		if (!mp3_fill_buffer(data))
			return DECODE_BREAK;
	}
	if (mad_header_decode(&data->frame.header, &data->stream)) {
		if ((data->stream).error == MAD_ERROR_LOSTSYNC &&
		    (data->stream).this_frame) {
			signed long tagsize = id3_tag_query((data->stream).
							    this_frame,
							    (data->stream).
							    bufend -
							    (data->stream).
							    this_frame);

			if (tagsize > 0) {
				if (tag && !(*tag)) {
					mp3_parse_id3(data, (size_t)tagsize,
						      tag);
				} else {
					mad_stream_skip(&(data->stream),
							tagsize);
				}
				return DECODE_CONT;
			}
		}
		if (MAD_RECOVERABLE((data->stream).error)) {
			return DECODE_SKIP;
		} else {
			if ((data->stream).error == MAD_ERROR_BUFLEN)
				return DECODE_CONT;
			else {
				g_warning("unrecoverable frame level error "
					  "(%s).\n",
					  mad_stream_errorstr(&data->stream));
				return DECODE_BREAK;
			}
		}
	}

	layer = data->frame.header.layer;
	if (!data->layer) {
		if (layer != MAD_LAYER_II && layer != MAD_LAYER_III) {
			/* Only layer 2 and 3 have been tested to work */
			return DECODE_SKIP;
		}
		data->layer = layer;
	} else if (layer != data->layer) {
		/* Don't decode frames with a different layer than the first */
		return DECODE_SKIP;
	}

	return DECODE_OK;
}

static void
scan_file (FILE * fd, int *length, int *bitrate)
{
    struct mad_stream stream;
    struct mad_header header;
    mad_timer_t timer;
    unsigned char buffer[8192];
    unsigned int buflen = 0;

    mad_stream_init (&stream);
    mad_header_init (&header);

    timer = mad_timer_zero;

    while (1)
    {
	if (buflen < 8192)
	{
            int bytes = 0;

            bytes = fread (buffer + buflen, 1, 8192 - buflen, fd);
            if (bytes <= 0)
		break;

            buflen += bytes;
	}

	mad_stream_buffer (&stream, buffer, buflen);

	while (1)
	{
            if (mad_header_decode (&header, &stream) == -1)
            {
		if (!MAD_RECOVERABLE (stream.error))
                    break;
		continue;
            }
            if (length)
		mad_timer_add (&timer, header.duration);

	}

	if (stream.error != MAD_ERROR_BUFLEN)
            break;

	memmove (buffer, stream.next_frame, &buffer[buflen] - stream.next_frame);
	buflen -= stream.next_frame - &buffer[0];
        SDL_Delay(1);
    }

    mad_header_finish (&header);
    mad_stream_finish (&stream);

    if (length)
	*length = mad_timer_count (timer, MAD_UNITS_MILLISECONDS);
}

static const void *mp_registersong (music_player_t *music, const void *data, unsigned len)
{
	mp_player_t *mp = (mp_player_t*)music;
  int i;
  int maxtry;
  int success = 0;

  // the MP3 standard doesn't include any global file header.  the only way to tell filetype
  // is to start decoding stuff.  you can't be too strict however because MP3 is resilient to
  // crap in the stream.

  // this routine is a bit slower than it could be, but apparently there are lots of files out
  // there with some dodgy stuff at the beginning.
    
  // if the stream begins with an ID3v2 magic, search hard and long for our first valid header
  if (memcmp (data, "ID3", 3) == 0)
    maxtry = 100;
  // otherwise, search for not so long
  else
    maxtry = 20;

  mad_stream_buffer (&mp->Stream, data, len);

  for (i = 0; i < maxtry; i++)
  {
    if (mad_header_decode (&mp->Header, &mp->Stream) != 0)
    {
      if (!MAD_RECOVERABLE (mp->Stream.error))
      {
        lprintf (LO_WARN, "mad_registersong failed: %s\n", mad_stream_errorstr (&mp->Stream));
        return NULL;
      }  
    }
    else
    {
      success++;
    }
  }

  // 80% to pass
  if (success < maxtry * 8 / 10)
  {
    lprintf (LO_WARN, "mad_registersong failed\n");
    return NULL;
  }
  
  lprintf (LO_INFO, "mad_registersong succeed. bitrate %lu samplerate %d\n", mp->Header.bitrate, mp->Header.samplerate);
 
  mp->mp_data = data;
  mp->mp_len = len;
  // handle not used
  return data;
}

/* Returns 1 if a recoverable error occured, 0 else. */
int mad_js_decode_frame(madfile_t *mf)
{
  int dec;

  dec = mad_frame_decode(&mf->frame, &mf->stream);
  if (dec) {
    if (MAD_RECOVERABLE(mf->stream.error)
        || mf->stream.error == MAD_ERROR_BUFLEN) {
      return 1;
    } else {
      _mad_js_raise(mad_stream_errorstr(&mf->stream));
    }
  }

  mad_synth_frame(&mf->synth, &mf->frame);

  return 0;
}

int LibMadWrapper::findValidHeader(struct mad_header &header)
{
    int ret;

    while ((ret = mad_header_decode(&header, this->stream)) != 0 && MAD_RECOVERABLE(this->stream->error))
    {
        if (this->stream->error == MAD_ERROR_LOSTSYNC)
        {
            long tagsize = id3_tag_query(this->stream->this_frame, this->stream->bufend - this->stream->this_frame);
            if (tagsize > 0)
            {
                mad_stream_skip(this->stream, tagsize);
                continue;
            }
        }
    }

    return ret;
}

static enum mp3_action
decodeNextFrame(struct mp3_data *data)
{
	if ((data->stream).buffer == NULL
	    || (data->stream).error == MAD_ERROR_BUFLEN) {
		if (!mp3_fill_buffer(data))
			return DECODE_BREAK;
	}
	if (mad_frame_decode(&data->frame, &data->stream)) {
#ifdef HAVE_ID3TAG
		if ((data->stream).error == MAD_ERROR_LOSTSYNC) {
			signed long tagsize = id3_tag_query((data->stream).
							    this_frame,
							    (data->stream).
							    bufend -
							    (data->stream).
							    this_frame);
			if (tagsize > 0) {
				mad_stream_skip(&(data->stream), tagsize);
				return DECODE_CONT;
			}
		}
#endif
		if (MAD_RECOVERABLE((data->stream).error)) {
			return DECODE_SKIP;
		} else {
			if ((data->stream).error == MAD_ERROR_BUFLEN)
				return DECODE_CONT;
			else {
				g_warning("unrecoverable frame level error "
					  "(%s).\n",
					  mad_stream_errorstr(&data->stream));
				return DECODE_BREAK;
			}
		}
	}

	return DECODE_OK;
}

static gboolean
xmms_mad_init (xmms_xform_t *xform)
{
	struct mad_frame frame;
	struct mad_stream stream;
	xmms_error_t err;
	guchar buf[40960];
	xmms_mad_data_t *data;
	int len;
	const gchar *metakey;

	g_return_val_if_fail (xform, FALSE);

	data = g_new0 (xmms_mad_data_t, 1);

	mad_stream_init (&data->stream);
	mad_frame_init (&data->frame);
	mad_synth_init (&data->synth);

	xmms_xform_private_data_set (xform, data);

	data->buffer_length = 0;

	data->synthpos = 0x7fffffff;

	mad_stream_init (&stream);
	mad_frame_init (&frame);

	len = xmms_xform_peek (xform, buf, 40960, &err);
	mad_stream_buffer (&stream, buf, len);

	while (mad_frame_decode (&frame, &stream) == -1) {
		if (!MAD_RECOVERABLE (stream.error)) {
			XMMS_DBG ("couldn't decode %02x %02x %02x %02x",buf[0],buf[1],buf[2],buf[3]);
			mad_frame_finish (&frame);
			mad_stream_finish (&stream);
			return FALSE;
		}
	}

	data->channels = frame.header.mode == MAD_MODE_SINGLE_CHANNEL ? 1 : 2;
	data->samplerate = frame.header.samplerate;


	if (frame.header.flags & MAD_FLAG_PROTECTION) {
		XMMS_DBG ("Frame has protection enabled");
		if (stream.anc_ptr.byte > stream.buffer + 2) {
			stream.anc_ptr.byte = stream.anc_ptr.byte - 2;
		}
	}

	data->samples_to_play = -1;

	data->xing = xmms_xing_parse (stream.anc_ptr);
	if (data->xing) {
		xmms_xing_lame_t *lame;
		XMMS_DBG ("File with Xing header!");

		metakey = XMMS_MEDIALIB_ENTRY_PROPERTY_IS_VBR;
		xmms_xform_metadata_set_int (xform, metakey, 1);

		if (xmms_xing_has_flag (data->xing, XMMS_XING_FRAMES)) {
			guint duration;
			mad_timer_t timer;

			timer = frame.header.duration;
			mad_timer_multiply (&timer, xmms_xing_get_frames (data->xing));
			duration = mad_timer_count (timer, MAD_UNITS_MILLISECONDS);

			XMMS_DBG ("XING duration %d", duration);

			metakey = XMMS_MEDIALIB_ENTRY_PROPERTY_DURATION;
			xmms_xform_metadata_set_int (xform, metakey, duration);

			if (xmms_xing_has_flag (data->xing, XMMS_XING_BYTES) && duration) {
				guint tmp;

				tmp = xmms_xing_get_bytes (data->xing) * ((guint64)8000) / duration;
				XMMS_DBG ("XING bitrate %d", tmp);
				metakey = XMMS_MEDIALIB_ENTRY_PROPERTY_BITRATE;
				xmms_xform_metadata_set_int (xform, metakey, tmp);
			}
		}

		lame = xmms_xing_get_lame (data->xing);
		if (lame) {
			/* FIXME: add a check for ignore_lame_headers from the medialib */
			data->frames_to_skip = 1;
			data->samples_to_skip = lame->start_delay;
			data->samples_to_play = ((guint64) xmms_xing_get_frames (data->xing) * 1152ULL) -
			                        lame->start_delay - lame->end_padding;
			XMMS_DBG ("Samples to skip in the beginning: %d, total: %" G_GINT64_FORMAT,
			          data->samples_to_skip, data->samples_to_play);
			/*
			metakey = XMMS_MEDIALIB_ENTRY_PROPERTY_GAIN_ALBUM;
			xmms_xform_metadata_set_int (xform, metakey, lame->audiophile_gain);

			metakey = XMMS_MEDIALIB_ENTRY_PROPERTY_PEAK_TRACK;
			xmms_xform_metadata_set_int (xform, metakey, lame->peak_amplitude);

//.........这里部分代码省略.........

static void mp_render_ex (void *dest, unsigned nsamp)
{
  short *sout = (short *) dest;

  int localerrors = 0;

  if (!mp_playing || mp_paused)
  {
    memset (dest, 0, nsamp * 4);
    return;
  }

  while (1)
  {
    // write any leftover data from last MP3 frame
    while (mp_leftoversamps > 0 && nsamp > 0)
    {
      short s = mp_fixtoshort (Synth.pcm.samples[0][mp_leftoversamppos]);
      *sout++ = s;
      if (Synth.pcm.channels == 2)
        s = mp_fixtoshort (Synth.pcm.samples[1][mp_leftoversamppos]);
      // if mono, just duplicate the first channel again
      *sout++ = s;

      mp_leftoversamps -= 1;
      mp_leftoversamppos += 1;
      nsamp -= 1;
    }
    if (nsamp == 0)
      return; // done
    
    // decode next valid MP3 frame
    while (mad_frame_decode (&Frame, &Stream) != 0)
    {
      if (MAD_RECOVERABLE (Stream.error))
      { // unspecified problem with one frame.
        // try the next frame, but bail if we get a bunch of crap in a row;
        // likely indicates a larger problem (and if we don't bail, we could
        // spend arbitrarily long amounts of time looking for the next good
        // packet)
        localerrors++;
        if (localerrors == 10)
        {
          lprintf (LO_WARN, "mad_frame_decode: Lots of errors.  Most recent %s\n", mad_stream_errorstr (&Stream));
          mp_playing = 0;
          memset (sout, 0, nsamp * 4);
          return;
        }
      }  
      else if (Stream.error == MAD_ERROR_BUFLEN)
      { // EOF
        // FIXME: in order to not drop the last frame, there must be at least MAD_BUFFER_GUARD
        // of extra bytes (with value 0) at the end of the file.  current implementation
        // drops last frame
        if (mp_looping)
        { // rewind, then go again
          mad_stream_buffer (&Stream, mp_data, mp_len);
          continue;
        }
        else
        { // stop
          mp_playing = 0;
          memset (sout, 0, nsamp * 4);
          return;
        }
      }
      else
      { // oh well.
        lprintf (LO_WARN, "mad_frame_decode: Unrecoverable error %s\n", mad_stream_errorstr (&Stream));
        mp_playing = 0;
        memset (sout, 0, nsamp * 4);
        return;
      }
    }

    // got a good frame, so synth it and dispatch it.
    mad_synth_frame (&Synth, &Frame);
    mp_leftoversamps = Synth.pcm.length;
    mp_leftoversamppos = 0;

  }
  // NOT REACHED
}

/* Reads the next frame from the file.  Returns true on success or
   false on failure. */
static int
read_next_frame(mad_data *mp3_mad) {
  if (mp3_mad->stream.buffer == NULL ||
      mp3_mad->stream.error == MAD_ERROR_BUFLEN) {
    size_t read_size;
    size_t remaining;
    unsigned char *read_start;

    /* There might be some bytes in the buffer left over from last
       time.  If so, move them down and read more bytes following
       them. */
    if (mp3_mad->stream.next_frame != NULL) {
      remaining = mp3_mad->stream.bufend - mp3_mad->stream.next_frame;
      memmove(mp3_mad->input_buffer, mp3_mad->stream.next_frame, remaining);
      read_start = mp3_mad->input_buffer + remaining;
      read_size = MAD_INPUT_BUFFER_SIZE - remaining;

    } else {
      read_size = MAD_INPUT_BUFFER_SIZE;
      read_start = mp3_mad->input_buffer;
      remaining = 0;
    }

    /* Now read additional bytes from the input file. */
    read_size = SDL_RWread(mp3_mad->src, read_start, 1, read_size);

    if (read_size <= 0) {
      if ((mp3_mad->status & (MS_input_eof | MS_input_error)) == 0) {
        if (read_size == 0) {
          mp3_mad->status |= MS_input_eof;
        } else {
          mp3_mad->status |= MS_input_error;
        }

        /* At the end of the file, we must stuff MAD_BUFFER_GUARD
           number of 0 bytes. */
        SDL_memset(read_start + read_size, 0, MAD_BUFFER_GUARD);
        read_size += MAD_BUFFER_GUARD;
      }
    }

    /* Now feed those bytes into the libmad stream. */
    mad_stream_buffer(&mp3_mad->stream, mp3_mad->input_buffer,
                      read_size + remaining);
    mp3_mad->stream.error = MAD_ERROR_NONE;
  }

  /* Now ask libmad to extract a frame from the data we just put in
     its buffer. */
  if (mad_frame_decode(&mp3_mad->frame, &mp3_mad->stream)) {
    if (MAD_RECOVERABLE(mp3_mad->stream.error)) {
      return 0;

    } else if (mp3_mad->stream.error == MAD_ERROR_BUFLEN) {
      return 0;

    } else {
      mp3_mad->status |= MS_decode_error;
      return 0;
    }
  }

  mp3_mad->frames_read++;
  mad_timer_add(&mp3_mad->next_frame_start, mp3_mad->frame.header.duration);

  return 1;
}

/* Following two functions are adapted from mad_timer, from the 
   libmad distribution */
void scan(void const *ptr, ssize_t len, buffer *buf)
{
    struct mad_stream stream;
    struct mad_header header;
    struct xing xing;
    
    unsigned long bitrate = 0;
    int has_xing = 0;
    int is_vbr = 0;

    mad_stream_init(&stream);
    mad_header_init(&header);

    mad_stream_buffer(&stream, ptr, len);

    buf->num_frames = 0;

    /* There are three ways of calculating the length of an mp3:
      1) Constant bitrate: One frame can provide the information
         needed: # of frames and duration. Just see how long it
         is and do the division.
      2) Variable bitrate: Xing tag. It provides the number of 
         frames. Each frame has the same number of samples, so
         just use that.
      3) All: Count up the frames and duration of each frames
         by decoding each one. We do this if we've no other
         choice, i.e. if it's a VBR file with no Xing tag.
    */

    while (1)
    {
        if (mad_header_decode(&header, &stream) == -1)
        {
            if (MAD_RECOVERABLE(stream.error))
                continue;
            else
                break;
        }

        /* Limit xing testing to the first frame header */
        if (!buf->num_frames++)
        {
            if(parse_xing(&xing, stream.anc_ptr, stream.anc_bitlen))
            {
                is_vbr = 1;
                
                if (xing.flags & XING_FRAMES)
                {
                    /* We use the Xing tag only for frames. If it doesn't have that
                       information, it's useless to us and we have to treat it as a
                       normal VBR file */
                    has_xing = 1;
                    buf->num_frames = xing.frames;
                    break;
                }
            }
        }                

        /* Test the first n frames to see if this is a VBR file */
        if (!is_vbr && !(buf->num_frames > 20))
        {
            if (bitrate && header.bitrate != bitrate)
            {
                is_vbr = 1;
            }
            
            else
            {
                bitrate = header.bitrate;
            }
        }
        
        /* We have to assume it's not a VBR file if it hasn't already been
           marked as one and we've checked n frames for different bitrates */
        else if (!is_vbr)
        {
            break;
        }
            
        mad_timer_add(&buf->duration, header.duration);
    }

    if (!is_vbr)
    {
        double time = (len * 8.0) / (header.bitrate); /* time in seconds */
        double timefrac = (double)time - ((long)(time));
        long nsamples = 32 * MAD_NSBSAMPLES(&header); /* samples per frame */
        
        /* samplerate is a constant */
        buf->num_frames = (long) (time * header.samplerate / nsamples);

        mad_timer_set(&buf->duration, (long)time, (long)(timefrac*100), 100);
    }
        
    else if (has_xing)
    {
        /* modify header.duration since we don't need it anymore */
        mad_timer_multiply(&header.duration, buf->num_frames);
//.........这里部分代码省略.........