mpeg4videostreamframer.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

Boolean MPEG4VideoStreamParser::getNextFrameBit(u_int8_t& result) {
  if (fNumBitsSeenSoFar/8 >= curFrameSize()) return False;

  u_int8_t nextByte = fStartOfFrame[fNumBitsSeenSoFar/8];
  result = (nextByte>>(7-fNumBitsSeenSoFar%8))&1;
  ++fNumBitsSeenSoFar;
  return True;
}

Boolean MPEG4VideoStreamParser::getNextFrameBits(unsigned numBits,
						 u_int32_t& result) {
  result = 0;
  for (unsigned i = 0; i < numBits; ++i) {
    u_int8_t nextBit;
    if (!getNextFrameBit(nextBit)) return False;
    result = (result<<1)|nextBit;
  }
  return True;
}

void MPEG4VideoStreamParser::analyzeVOLHeader() {
  // Extract timing information (in particular,
  // "vop_time_increment_resolution") from the VOL Header:
  fNumBitsSeenSoFar = 41;
  do {
    u_int8_t is_object_layer_identifier;
    if (!getNextFrameBit(is_object_layer_identifier)) break;
    if (is_object_layer_identifier) fNumBitsSeenSoFar += 7;

    u_int32_t aspect_ratio_info;
    if (!getNextFrameBits(4, aspect_ratio_info)) break;
    if (aspect_ratio_info == 15 /*extended_PAR*/) fNumBitsSeenSoFar += 16;

    u_int8_t vol_control_parameters;
    if (!getNextFrameBit(vol_control_parameters)) break;
    if (vol_control_parameters) {
      fNumBitsSeenSoFar += 3; // chroma_format; low_delay
      u_int8_t vbw_parameters;
      if (!getNextFrameBit(vbw_parameters)) break;
      if (vbw_parameters) fNumBitsSeenSoFar += 79;
    }

    fNumBitsSeenSoFar += 2; // video_object_layer_shape
    u_int8_t marker_bit;
    if (!getNextFrameBit(marker_bit)) break;
    if (marker_bit != 1) { // sanity check
      usingSource()->envir() << "MPEG4VideoStreamParser::analyzeVOLHeader(): marker_bit 1 not set!\n";
      break;
    }

    if (!getNextFrameBits(16, vop_time_increment_resolution)) break;
#ifdef DEBUG
    fprintf(stderr, "vop_time_increment_resolution: %d\n", vop_time_increment_resolution);
#endif
    if (vop_time_increment_resolution == 0) {
      usingSource()->envir() << "MPEG4VideoStreamParser::analyzeVOLHeader(): vop_time_increment_resolution is zero!\n";
      break;
    }
    // Compute how many bits are necessary to represent this:
    fNumVTIRBits = 0;
    for (unsigned test = vop_time_increment_resolution; test>0; test /= 2) {
      ++fNumVTIRBits;
    }

    if (!getNextFrameBit(marker_bit)) break;
    if (marker_bit != 1) { // sanity check
      usingSource()->envir() << "MPEG4VideoStreamParser::analyzeVOLHeader(): marker_bit 2 not set!\n";
      break;
    }

    if (!getNextFrameBit(fixed_vop_rate)) break;
    if (fixed_vop_rate) {
      // Get the following "fixed_vop_time_increment":
      if (!getNextFrameBits(fNumVTIRBits, fixed_vop_time_increment)) break;
#ifdef DEBUG
      fprintf(stderr, "fixed_vop_time_increment: %d\n", fixed_vop_time_increment);
      if (fixed_vop_time_increment == 0) {
	usingSource()->envir() << "MPEG4VideoStreamParser::analyzeVOLHeader(): fixed_vop_time_increment is zero!\n";
      }
#endif
    }
    // Use "vop_time_increment_resolution" as the 'frame rate'
    // (really, 'tick rate'):
    usingSource()->fFrameRate = (double)vop_time_increment_resolution;
#ifdef DEBUG
    fprintf(stderr, "fixed_vop_rate: %d; 'frame' (really tick) rate: %f\n", fixed_vop_rate, usingSource()->fFrameRate);
#endif

    return;
  } while (0);

  if (fNumBitsSeenSoFar/8 >= curFrameSize()) {
    char errMsg[200];
    sprintf(errMsg, "Not enough bits in VOL header: %d/8 >= %d\n", fNumBitsSeenSoFar, curFrameSize());
    usingSource()->envir() << errMsg;
  }
}

unsigned MPEG4VideoStreamParser::parseVideoObjectLayer() {
#ifdef DEBUG
  fprintf(stderr, "parsing VideoObjectLayer\n");
#endif
  // The first 4 bytes must be a "video_object_layer_start_code".
  // If not, this is a 'short video header', which we currently
  // don't support:
  u_int32_t next4Bytes = get4Bytes();
  if (!isVideoObjectLayerStartCode(next4Bytes)) {
    usingSource()->envir() << "MPEG4VideoStreamParser::parseVideoObjectLayer(): This appears to be a 'short video header', which we current don't support\n";
  }

  // Now, copy all bytes that we see, up until we reach
  // a GROUP_VOP_START_CODE or a VOP_START_CODE:
  do {
    saveToNextCode(next4Bytes);
  } while (next4Bytes != GROUP_VOP_START_CODE
	   && next4Bytes != VOP_START_CODE);
  
  analyzeVOLHeader();

  setParseState((next4Bytes == GROUP_VOP_START_CODE)
                ? PARSING_GROUP_OF_VIDEO_OBJECT_PLANE
		: PARSING_VIDEO_OBJECT_PLANE);

  // Compute this frame's presentation time:
  usingSource()->computePresentationTime(fTotalTicksSinceLastTimeCode);

  // This header ends the 'configuration' information:
  usingSource()->appendToNewConfig(fStartOfFrame, curFrameSize());
  usingSource()->completeNewConfig();

  return curFrameSize();
}

unsigned MPEG4VideoStreamParser::parseGroupOfVideoObjectPlane() {
#ifdef DEBUG
  fprintf(stderr, "parsing GroupOfVideoObjectPlane\n");
#endif
  // Note that we've already read the GROUP_VOP_START_CODE
  save4Bytes(GROUP_VOP_START_CODE);

  // Next, extract the (18-bit) time code from the next 3 bytes:
  u_int8_t next3Bytes[3];
  getBytes(next3Bytes, 3);
  saveByte(next3Bytes[0]);saveByte(next3Bytes[1]);saveByte(next3Bytes[2]); 
  unsigned time_code
    = (next3Bytes[0]<<10)|(next3Bytes[1]<<2)|(next3Bytes[2]>>6);
  unsigned time_code_hours    = (time_code&0x0003E000)>>13;
  unsigned time_code_minutes  = (time_code&0x00001F80)>>7;
#if defined(DEBUG) || defined(DEBUG_TIMESTAMPS)
  Boolean marker_bit          = (time_code&0x00000040) != 0;
#endif
  unsigned time_code_seconds  = (time_code&0x0000003F);
#if defined(DEBUG) || defined(DEBUG_TIMESTAMPS)
  fprintf(stderr, "time_code: 0x%05x, hours %d, minutes %d, marker_bit %d, seconds %d\n", time_code, time_code_hours, time_code_minutes, marker_bit, time_code_seconds);
#endif

  // Now, copy all bytes that we see, up until we reach a VOP_START_CODE:
  u_int32_t next4Bytes = get4Bytes();
  while (next4Bytes != VOP_START_CODE) {
    saveToNextCode(next4Bytes);
  }
  
  // Compute this frame's presentation time:
  usingSource()->computePresentationTime(fTotalTicksSinceLastTimeCode);

  // Record the time code:
  usingSource()->setTimeCode(time_code_hours, time_code_minutes,
                             time_code_seconds, 0, 0);
    // Note: Because the GOV header can appear anywhere (not just at a 1s point), we
    // don't pass "fTotalTicksSinceLastTimeCode" as the "picturesSinceLastGOP" parameter.
  fSecondsSinceLastTimeCode = 0;
  if (fixed_vop_rate) fTotalTicksSinceLastTimeCode = 0;

  setParseState(PARSING_VIDEO_OBJECT_PLANE);

  return curFrameSize();
}

unsigned MPEG4VideoStreamParser::parseVideoObjectPlane() {
#ifdef DEBUG
  fprintf(stderr, "#parsing VideoObjectPlane\n");
#endif
  // Note that we've already read the VOP_START_CODE
  save4Bytes(VOP_START_CODE);

  // Get the "vop_coding_type" from the next byte:
  u_int8_t nextByte = get1Byte(); saveByte(nextByte);
  u_int8_t vop_coding_type = nextByte>>6;

  // Next, get the "modulo_time_base" by counting the '1' bits that follow.
  // We look at the next 32-bits only.  This should be enough in most cases.
  u_int32_t next4Bytes = get4Bytes();
  u_int32_t timeInfo = (nextByte<<(32-6))|(next4Bytes>>6);
  unsigned modulo_time_base = 0;
  u_int32_t mask = 0x80000000;
  while ((timeInfo&mask) != 0) {
    ++modulo_time_base;
    mask >>= 1;
  }
  mask >>= 1;

  // Check the following marker bit:
  if ((timeInfo&mask) == 0) {
    usingSource()->envir() << "MPEG4VideoStreamParser::parseVideoObjectPlane(): marker bit not set!\n";
  }
  mask >>= 1;

  // Then, get the "vop_time_increment".
  // First, make sure we have enough bits left for this:
  if ((mask>>(fNumVTIRBits-1)) == 0) {
    usingSource()->envir() << "MPEG4VideoStreamParser::parseVideoObjectPlane(): 32-bits are not enough to get \"vop_time_increment\"!\n";
  }
  unsigned vop_time_increment = 0;
  for (unsigned i = 0; i < fNumVTIRBits; ++i) {
    vop_time_increment |= timeInfo&mask;
    mask >>= 1;
  }
  while (mask != 0) {
    vop_time_increment >>= 1;
    mask >>= 1;
  }
#ifdef DEBUG
  fprintf(stderr, "vop_coding_type: %d(%c), modulo_time_base: %d, vop_time_increment: %d\n", vop_coding_type, "IPBS"[vop_coding_type], modulo_time_base, vop_time_increment);
#endif
    
  // Now, copy all bytes that we see, up until we reach a code of some sort:
  saveToNextCode(next4Bytes);
  
  // Update our counters based on the frame timing information that we saw:
  if (fixed_vop_time_increment > 0) {
    // This is a 'fixed_vop_rate' stream.  Use 'fixed_vop_time_increment':
    usingSource()->fPictureCount += fixed_vop_time_increment;
    if (vop_time_increment > 0 || modulo_time_base > 0) {
      fTotalTicksSinceLastTimeCode += fixed_vop_time_increment;
      // Note: "fSecondsSinceLastTimeCode" and "fPrevNewTotalTicks" are not used.
    }
  } else {
    // Use 'vop_time_increment':
    unsigned newTotalTicks
      = (fSecondsSinceLastTimeCode + modulo_time_base)*vop_time_increment_resolution
      + vop_time_increment;
    if (newTotalTicks == fPrevNewTotalTicks && fPrevNewTotalTicks > 0) {
      // This is apparently a buggy MPEG-4 video stream, because
      // "vop_time_increment" did not change.  Overcome this error,
      // by pretending that it did change.
#ifdef DEBUG
      fprintf(stderr, "Buggy MPEG-4 video stream: \"vop_time_increment\" did not change!\n");
#endif
      // The following assumes that we don't have 'B' frames.  If we do, then TARFU!
      usingSource()->fPictureCount += vop_time_increment;
      fTotalTicksSinceLastTimeCode += vop_time_increment;
      fSecondsSinceLastTimeCode += modulo_time_base;
    } else {
      if (newTotalTicks < fPrevNewTotalTicks && vop_coding_type != 2/*B*/
	  && modulo_time_base == 0 && vop_time_increment == 0) {
	// This is another kind of buggy MPEG-4 video stream, in which
	// "vop_time_increment" wraps around, but without
	// "modulo_time_base" changing.  Overcome this by pretending that
	// "vop_time_increment" really did wrap around:
#ifdef DEBUG
	fprintf(stderr, "Buggy MPEG-4 video stream: \"vop_time_increment\" wrapped around, but without \"modulo_time_base\" changing!\n");
#endif
	++fSecondsSinceLastTimeCode;
	newTotalTicks += vop_time_increment_resolution;
      }
      fPrevNewTotalTicks = newTotalTicks;
      if (vop_coding_type != 2/*B*/) {
	int pictureCountDelta = newTotalTicks - fTotalTicksSinceLastTimeCode;
	if (pictureCountDelta <= 0) pictureCountDelta = fPrevPictureCountDelta;
	    // ensures that the picture count is always increasing
	usingSource()->fPictureCount += pictureCountDelta;
	fPrevPictureCountDelta = pictureCountDelta;
	fTotalTicksSinceLastTimeCode = newTotalTicks;
	fSecondsSinceLastTimeCode += modulo_time_base;
      }
    }
  }
  
  // The next thing to parse depends on the code that we just saw,
  // but we are assumed to have ended the current picture: 
  usingSource()->fPictureEndMarker = True; // HACK #####
  switch (next4Bytes) {
  case VISUAL_OBJECT_SEQUENCE_END_CODE: {
    setParseState(PARSING_VISUAL_OBJECT_SEQUENCE_END_CODE);
    break;
  }
  case VISUAL_OBJECT_SEQUENCE_START_CODE: {
    setParseState(PARSING_VISUAL_OBJECT_SEQUENCE_SEEN_CODE);
    break;
  }
  case GROUP_VOP_START_CODE: {
    setParseState(PARSING_GROUP_OF_VIDEO_OBJECT_PLANE);
    break;
  }
  case VOP_START_CODE: {
    setParseState(PARSING_VIDEO_OBJECT_PLANE);
    break;
  }
  default: {
    usingSource()->envir() << "MPEG4VideoStreamParser::parseVideoObjectPlane(): Saw unexpected code "
			   << (void*)next4Bytes << "\n";
    setParseState(PARSING_VIDEO_OBJECT_PLANE); // the safest way to recover...
    break;
  }
  }

  // Compute this frame's presentation time:
  usingSource()->computePresentationTime(fTotalTicksSinceLastTimeCode);

  return curFrameSize();
}

unsigned MPEG4VideoStreamParser::parseVisualObjectSequenceEndCode() {
#ifdef DEBUG
  fprintf(stderr, "parsing VISUAL_OBJECT_SEQUENCE_END_CODE\n");
#endif
  // Note that we've already read the VISUAL_OBJECT_SEQUENCE_END_CODE
  save4Bytes(VISUAL_OBJECT_SEQUENCE_END_CODE);

  setParseState(PARSING_VISUAL_OBJECT_SEQUENCE);

  // Treat this as if we had ended a picture:
  usingSource()->fPictureEndMarker = True; // HACK #####

  return curFrameSize();
}