mpeg1or2demux.cpp

流媒体传输协议的实现代码,非常有用.可以支持rtsp mms等流媒体传输协议

void MPEGProgramStreamParser::parsePackHeader() {
#ifdef DEBUG
  fprintf(stderr, "parsing pack header\n"); fflush(stderr);
#endif
  unsigned first4Bytes;
  while (1) {
    first4Bytes = test4Bytes();

    // We're supposed to have a pack header here, but check also for
    // a system header or a PES packet, just in case:
    if (first4Bytes == PACK_START_CODE) {
      skipBytes(4);
      break;
    } else if (first4Bytes == SYSTEM_HEADER_START_CODE) {
#ifdef DEBUG
      fprintf(stderr, "found system header instead of pack header\n");
#endif
      setParseState(PARSING_SYSTEM_HEADER);
      return;
    } else if (isPacketStartCode(first4Bytes)) {
#ifdef DEBUG
      fprintf(stderr, "found packet start code 0x%02x instead of pack header\n", first4Bytes);
#endif
      setParseState(PARSING_PES_PACKET);
      return;
    }

    setParseState(PARSING_PACK_HEADER); // ensures we progress over bad data
    if ((first4Bytes&0xFF) > 1) { // a system code definitely doesn't start here
      skipBytes(4);
    } else {
      skipBytes(1);
    }
  }
  
  // The size of the pack header differs depending on whether it's
  // MPEG-1 or MPEG-2.  The next byte tells us this: 
  unsigned char nextByte = get1Byte();
  MPEG1or2Demux::SCR& scr = fUsingSource->fLastSeenSCR; // alias
  if ((nextByte&0xF0) == 0x20) { // MPEG-1
    fUsingSource->fMPEGversion = 1;
    scr.highBit =  (nextByte&0x08)>>3;
    scr.remainingBits = (nextByte&0x06)<<29;
    unsigned next4Bytes = get4Bytes();
    scr.remainingBits |= (next4Bytes&0xFFFE0000)>>2;
    scr.remainingBits |= (next4Bytes&0x0000FFFE)>>1;
    scr.extension = 0;
    scr.isValid = True;
    skipBits(24);

#if defined(DEBUG_TIMESTAMPS) || defined(DEBUG_SCR_TIMESTAMPS)
    fprintf(stderr, "pack hdr system_clock_reference_base: 0x%x",
	    scr.highBit);
    fprintf(stderr, "%08x\n", scr.remainingBits);
#endif
  } else if ((nextByte&0xC0) == 0x40) { // MPEG-2
    fUsingSource->fMPEGversion = 2;
    scr.highBit =  (nextByte&0x20)>>5;
    scr.remainingBits = (nextByte&0x18)<<27;
    scr.remainingBits |= (nextByte&0x03)<<28;
    unsigned next4Bytes = get4Bytes();
    scr.remainingBits |= (next4Bytes&0xFFF80000)>>4;
    scr.remainingBits |= (next4Bytes&0x0003FFF8)>>3;
    scr.extension = (next4Bytes&0x00000003)<<7;
    next4Bytes = get4Bytes();
    scr.extension |= (next4Bytes&0xFE000000)>>25;
    scr.isValid = True;
    skipBits(5);

#if defined(DEBUG_TIMESTAMPS) || defined(DEBUG_SCR_TIMESTAMPS)
    fprintf(stderr, "pack hdr system_clock_reference_base: 0x%x",
	    scr.highBit);
    fprintf(stderr, "%08x\n", scr.remainingBits);
    fprintf(stderr, "pack hdr system_clock_reference_extension: 0x%03x\n",
	    scr.extension);
#endif
    unsigned char pack_stuffing_length = getBits(3);
    skipBytes(pack_stuffing_length);
  } else { // unknown
    fUsingSource->envir() << "StreamParser::parsePack() saw strange byte "
			  << (void*)nextByte
			  << " following pack_start_code\n";
  }
  
  // Check for a System Header next:
  setParseState(PARSING_SYSTEM_HEADER);
}  

void MPEGProgramStreamParser::parseSystemHeader() {
#ifdef DEBUG
  fprintf(stderr, "parsing system header\n"); fflush(stderr);
#endif
  unsigned next4Bytes = test4Bytes();
  if (next4Bytes != SYSTEM_HEADER_START_CODE) {
    // The system header was optional.  Look for a PES Packet instead:
    setParseState(PARSING_PES_PACKET);
    return;
  }
  
#ifdef DEBUG
  fprintf(stderr, "saw system_header_start_code\n"); fflush(stderr);
#endif
  skipBytes(4); // we've already seen the system_header_start_code
  
  unsigned short remaining_header_length = get2Bytes();
  
  // According to the MPEG-1 and MPEG-2 specs, "remaining_header_length" should be
  // at least 6 bytes.  Check this now:
  if (remaining_header_length < 6) {
    fUsingSource->envir() << "StreamParser::parseSystemHeader(): saw strange header_length: "
			  << remaining_header_length << " < 6\n";
  }
  skipBytes(remaining_header_length);
  
  // Check for a PES Packet next:
  setParseState(PARSING_PES_PACKET);
}

#define private_stream_1 0xBD
#define private_stream_2 0xBF

// A test for stream ids that are exempt from normal PES packet header parsing
Boolean MPEGProgramStreamParser
::isSpecialStreamId(unsigned char stream_id) const {
  if (stream_id == RAW_PES) return True; // hack

  if (fUsingSource->fMPEGversion == 1) {
    return stream_id == private_stream_2;
  } else { // assume MPEG-2
    if (stream_id <= private_stream_2) {
      return stream_id != private_stream_1;
    } else if ((stream_id&0xF0) == 0xF0) {
      unsigned char lower4Bits = stream_id&0x0F;
      return lower4Bits <= 2 || lower4Bits == 0x8 || lower4Bits == 0xF;
    } else {
      return False;
    }
  }
}

#define READER_NOT_READY 2 

unsigned char MPEGProgramStreamParser::parsePESPacket() {
#ifdef DEBUG
  fprintf(stderr, "parsing PES packet\n"); fflush(stderr);
#endif
  unsigned next4Bytes = test4Bytes();
  if (!isPacketStartCode(next4Bytes)) {
    // The PES Packet was optional.  Look for a Pack Header instead:
    setParseState(PARSING_PACK_HEADER);
    return 0;
  }
  
#ifdef DEBUG
  fprintf(stderr, "saw packet_start_code_prefix\n"); fflush(stderr);
#endif
  skipBytes(3); // we've already seen the packet_start_code_prefix

  unsigned char stream_id = get1Byte();
#if defined(DEBUG) || defined(DEBUG_TIMESTAMPS)
  unsigned char streamNum = stream_id;
  char* streamTypeStr;
  if ((stream_id&0xE0) == 0xC0) {
    streamTypeStr = "audio";
    streamNum = stream_id&~0xE0;
  } else if ((stream_id&0xF0) == 0xE0) {
    streamTypeStr = "video";
    streamNum = stream_id&~0xF0;
  } else if (stream_id == 0xbc) {
    streamTypeStr = "reserved";
  } else if (stream_id == 0xbd) {
    streamTypeStr = "private_1";
  } else if (stream_id == 0xbe) {
    streamTypeStr = "padding";
  } else if (stream_id == 0xbf) {
    streamTypeStr = "private_2";
  } else {
    streamTypeStr = "unknown";
  }
#endif
#ifdef DEBUG
  static unsigned frameCount = 1;
  fprintf(stderr, "%d, saw %s stream: 0x%02x\n", frameCount, streamTypeStr, streamNum); fflush(stderr);
#endif
  
  unsigned short PES_packet_length = get2Bytes();
#ifdef DEBUG
  fprintf(stderr, "PES_packet_length: %d\n", PES_packet_length); fflush(stderr);
#endif

  // Parse over the rest of the header, until we get to the packet data itself.
  // This varies depending upon the MPEG version:
  if (fUsingSource->fOutput[RAW_PES].isPotentiallyReadable) {
    // Hack: We've been asked to return raw PES packets, for every stream:
    stream_id = RAW_PES;
  } 
  unsigned savedParserOffset = curOffset();
#ifdef DEBUG_TIMESTAMPS
  unsigned char pts_highBit = 0;
  unsigned pts_remainingBits = 0;
  unsigned char dts_highBit = 0;
  unsigned dts_remainingBits = 0;
#endif
  if (fUsingSource->fMPEGversion == 1) {
    if (!isSpecialStreamId(stream_id)) {
      unsigned char nextByte;
      while ((nextByte = get1Byte()) == 0xFF) { // stuffing_byte
      }
      if ((nextByte&0xC0) == 0x40) { // '01'
	skipBytes(1);
	nextByte = get1Byte();
      }
      if ((nextByte&0xF0) == 0x20) { // '0010'
#ifdef DEBUG_TIMESTAMPS
	pts_highBit =  (nextByte&0x08)>>3;
	pts_remainingBits = (nextByte&0x06)<<29;
	unsigned next4Bytes = get4Bytes();
	pts_remainingBits |= (next4Bytes&0xFFFE0000)>>2;
	pts_remainingBits |= (next4Bytes&0x0000FFFE)>>1;
#else
	skipBytes(4);
#endif
      } else if ((nextByte&0xF0) == 0x30) { // '0011'
#ifdef DEBUG_TIMESTAMPS
	pts_highBit =  (nextByte&0x08)>>3;
	pts_remainingBits = (nextByte&0x06)<<29;
	unsigned next4Bytes = get4Bytes();
	pts_remainingBits |= (next4Bytes&0xFFFE0000)>>2;
	pts_remainingBits |= (next4Bytes&0x0000FFFE)>>1;

	nextByte = get1Byte();
	dts_highBit =  (nextByte&0x08)>>3;
	dts_remainingBits = (nextByte&0x06)<<29;
	next4Bytes = get4Bytes();
	dts_remainingBits |= (next4Bytes&0xFFFE0000)>>2;
	dts_remainingBits |= (next4Bytes&0x0000FFFE)>>1;
#else
	skipBytes(9);
#endif
      }
    }
  } else { // assume MPEG-2
    if (!isSpecialStreamId(stream_id)) {
      // Fields in the next 3 bytes determine the size of the rest:
      unsigned next3Bytes = getBits(24);
#ifdef DEBUG_TIMESTAMPS
      unsigned char PTS_DTS_flags       = (next3Bytes&0x00C000)>>14;
#endif
#ifdef undef
      unsigned char ESCR_flag           = (next3Bytes&0x002000)>>13;
      unsigned char ES_rate_flag        = (next3Bytes&0x001000)>>12;
      unsigned char DSM_trick_mode_flag = (next3Bytes&0x000800)>>11;
#endif
      unsigned char PES_header_data_length = (next3Bytes&0x0000FF);
#ifdef DEBUG
      fprintf(stderr, "PES_header_data_length: 0x%02x\n", PES_header_data_length); fflush(stderr);
#endif
#ifdef DEBUG_TIMESTAMPS
      if (PTS_DTS_flags == 0x2 && PES_header_data_length >= 5) {
	unsigned char nextByte = get1Byte();
	pts_highBit =  (nextByte&0x08)>>3;
	pts_remainingBits = (nextByte&0x06)<<29;
	unsigned next4Bytes = get4Bytes();
	pts_remainingBits |= (next4Bytes&0xFFFE0000)>>2;
	pts_remainingBits |= (next4Bytes&0x0000FFFE)>>1;

	skipBytes(PES_header_data_length-5);
      } else if (PTS_DTS_flags == 0x3 && PES_header_data_length >= 10) {
	unsigned char nextByte = get1Byte();
	pts_highBit =  (nextByte&0x08)>>3;
	pts_remainingBits = (nextByte&0x06)<<29;
	unsigned next4Bytes = get4Bytes();
	pts_remainingBits |= (next4Bytes&0xFFFE0000)>>2;
	pts_remainingBits |= (next4Bytes&0x0000FFFE)>>1;

	nextByte = get1Byte();
	dts_highBit =  (nextByte&0x08)>>3;
	dts_remainingBits = (nextByte&0x06)<<29;
	next4Bytes = get4Bytes();
	dts_remainingBits |= (next4Bytes&0xFFFE0000)>>2;
	dts_remainingBits |= (next4Bytes&0x0000FFFE)>>1;

	skipBytes(PES_header_data_length-10);
      }
#else
      skipBytes(PES_header_data_length);
#endif
    }
  }
#ifdef DEBUG_TIMESTAMPS
  fprintf(stderr, "%s stream, ", streamTypeStr);
  fprintf(stderr, "packet presentation_time_stamp: 0x%x", pts_highBit);
  fprintf(stderr, "%08x\n", pts_remainingBits);
  fprintf(stderr, "\t\tpacket decoding_time_stamp: 0x%x", dts_highBit);
  fprintf(stderr, "%08x\n", dts_remainingBits);
#endif

  // The rest of the packet will be the "PES_packet_data_byte"s
  // Make sure that "PES_packet_length" was consistent with where we are now:
  unsigned char acquiredStreamIdTag = 0;
  unsigned currentParserOffset = curOffset();
  unsigned bytesSkipped = currentParserOffset - savedParserOffset;
  if (stream_id == RAW_PES) {
    restoreSavedParserState(); // so we deliver from the beginning of the PES packet
    PES_packet_length += 6; // to include the whole of the PES packet
    bytesSkipped = 0;
  }
  if (PES_packet_length < bytesSkipped) {
    fUsingSource->envir() << "StreamParser::parsePESPacket(): saw inconsistent PES_packet_length "
			  << PES_packet_length << " < "
			  << bytesSkipped << "\n";
  } else {
    PES_packet_length -= bytesSkipped;
#ifdef DEBUG
    unsigned next4Bytes = test4Bytes(); 
#endif

    // Check whether our using source is interested in this stream type.
    // If so, deliver the frame to him:
    MPEG1or2Demux::OutputDescriptor_t& out = fUsingSource->fOutput[stream_id]; 
    if (out.isCurrentlyAwaitingData) {
      unsigned numBytesToCopy;
      if (PES_packet_length > out.maxSize) {
	fUsingSource->envir() << "MPEGProgramStreamParser::parsePESPacket() error: PES_packet_length ("
			      << PES_packet_length
			      << ") exceeds max frame size asked for ("
			      << out.maxSize << ")\n";
	numBytesToCopy = out.maxSize;
      } else {
	numBytesToCopy = PES_packet_length;
      }

      getBytes(out.to, numBytesToCopy);
      out.frameSize = numBytesToCopy;
#ifdef DEBUG
      fprintf(stderr, "%d, %d bytes of PES_packet_data (out.maxSize: %d); first 4 bytes: 0x%08x\n", frameCount, numBytesToCopy, out.maxSize, next4Bytes); fflush(stderr);
#endif
      // set out.presentationTime later #####
      acquiredStreamIdTag = stream_id;
      PES_packet_length -= numBytesToCopy;
    } else if (out.isCurrentlyActive) {
      // Someone has been reading this stream, but isn't right now.
      // We can't deliver this frame until he asks for it, so punt for now.
      // The next time he asks for a frame, he'll get it.
#ifdef DEBUG
      fprintf(stderr, "%d, currently undeliverable PES data; first 4 bytes: 0x%08x - currently undeliverable!\n", frameCount, next4Bytes); fflush(stderr);
#endif
      restoreSavedParserState(); // so we read from the beginning next time
      fUsingSource->fHaveUndeliveredData = True;
      throw READER_NOT_READY;
    } else if (out.isPotentiallyReadable &&
	       out.savedDataTotalSize + PES_packet_length < 1000000 /*limit*/) {
      // Someone is interested in this stream, but hasn't begun reading it yet.
      // Save this data, so that the reader will get it when he later asks for it.
      unsigned char* buf = new unsigned char[PES_packet_length];
      getBytes(buf, PES_packet_length);
      MPEG1or2Demux::OutputDescriptor::SavedData* savedData
	= new MPEG1or2Demux::OutputDescriptor::SavedData(buf, PES_packet_length);
      if (out.savedDataHead == NULL) {
	out.savedDataHead = out.savedDataTail = savedData;
      } else {
	out.savedDataTail->next = savedData;
	out.savedDataTail = savedData;
      }
      out.savedDataTotalSize += PES_packet_length;
      PES_packet_length = 0;
    }
    skipBytes(PES_packet_length);
  }

  // Check for another PES Packet next:
  setParseState(PARSING_PES_PACKET);
#ifdef DEBUG
  ++frameCount;
#endif
 return acquiredStreamIdTag;
}