liveMedia/MPEG2IndexFromTransportStream.cpp

/**********
This library is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the
Free Software Foundation; either version 3 of the License, or (at your
option) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.)

This library is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
more details.

You should have received a copy of the GNU Lesser General Public License
along with this library; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
**********/
// "liveMedia"
// Copyright (c) 1996-2020 Live Networks, Inc.  All rights reserved.
// A filter that produces a sequence of I-frame indices from a MPEG-2 Transport Stream
// Implementation

#include "MPEG2IndexFromTransportStream.hh"

////////// IndexRecord definition //////////

enum RecordType {
  RECORD_UNPARSED = 0,
  RECORD_VSH = 1, // a MPEG Video Sequence Header
  RECORD_GOP = 2,
  RECORD_PIC_NON_IFRAME = 3, // includes slices
  RECORD_PIC_IFRAME = 4, // includes slices
  RECORD_NAL_H264_SPS = 5, // H.264
  RECORD_NAL_H264_PPS = 6, // H.264
  RECORD_NAL_H264_SEI = 7, // H.264
  RECORD_NAL_H264_NON_IFRAME = 8, // H.264
  RECORD_NAL_H264_IFRAME = 9, // H.264
  RECORD_NAL_H264_OTHER = 10, // H.264
  RECORD_NAL_H265_VPS = 11, // H.265
  RECORD_NAL_H265_SPS = 12, // H.265
  RECORD_NAL_H265_PPS = 13, // H.265
  RECORD_NAL_H265_NON_IFRAME = 14, // H.265
  RECORD_NAL_H265_IFRAME = 15, // H.265
  RECORD_NAL_H265_OTHER = 16, // H.265
  RECORD_JUNK
};

class IndexRecord {
public:
  IndexRecord(u_int8_t startOffset, u_int8_t size,
	      unsigned long transportPacketNumber, float pcr);
  virtual ~IndexRecord();

  RecordType& recordType() { return fRecordType; }
  void setFirstFlag() { fRecordType = (RecordType)(((u_int8_t)fRecordType) | 0x80); }
  u_int8_t startOffset() const { return fStartOffset; }
  u_int8_t& size() { return fSize; }
  float pcr() const { return fPCR; }
  unsigned long transportPacketNumber() const { return fTransportPacketNumber; }

  IndexRecord* next() const { return fNext; }
  void addAfter(IndexRecord* prev);
  void unlink();

private:
  // Index records are maintained in a doubly-linked list:
  IndexRecord* fNext;
  IndexRecord* fPrev;

  RecordType fRecordType;
  u_int8_t fStartOffset; // within the Transport Stream packet
  u_int8_t fSize; // in bytes, following "fStartOffset".
  // Note: fStartOffset + fSize <= TRANSPORT_PACKET_SIZE
  float fPCR;
  unsigned long fTransportPacketNumber;
};

#ifdef DEBUG
static char const* recordTypeStr[] = {
  "UNPARSED",
  "VSH",
  "GOP",
  "PIC(non-I-frame)",
  "PIC(I-frame)",
  "SPS (H.264)",
  "PPS (H.264)",
  "SEI (H.264)",
  "H.264 non-I-frame",
  "H.264 I-frame",
  "other NAL unit (H.264)",
  "VPS (H.265)",
  "SPS (H.265)",
  "PPS (H.265)",
  "H.265 non-I-frame",
  "H.265 I-frame",
  "other NAL unit (H.265)",
  "JUNK"
};

UsageEnvironment& operator<<(UsageEnvironment& env, IndexRecord& r) {
  return env << "[" << ((r.recordType()&0x80) != 0 ? "1" : "")
	     << recordTypeStr[r.recordType()&0x7F] << ":"
	     << (unsigned)r.transportPacketNumber() << ":" << r.startOffset()
	     << "(" << r.size() << ")@" << r.pcr() << "]";
}
#endif


////////// MPEG2IFrameIndexFromTransportStream implementation //////////

MPEG2IFrameIndexFromTransportStream*
MPEG2IFrameIndexFromTransportStream::createNew(UsageEnvironment& env,
					       FramedSource* inputSource) {
  return new MPEG2IFrameIndexFromTransportStream(env, inputSource);
}

// The largest expected frame size (in bytes):
#define MAX_FRAME_SIZE 400000

// Make our parse buffer twice as large as this, to ensure that at least one
// complete frame will fit inside it:
#define PARSE_BUFFER_SIZE (2*MAX_FRAME_SIZE)

// The PID used for the PAT (as defined in the MPEG Transport Stream standard):
#define PAT_PID 0

MPEG2IFrameIndexFromTransportStream
::MPEG2IFrameIndexFromTransportStream(UsageEnvironment& env,
				      FramedSource* inputSource)
  : FramedFilter(env, inputSource),
    fIsH264(False), fIsH265(False),
    fInputTransportPacketCounter((unsigned)-1), fClosureNumber(0), fLastContinuityCounter(~0),
    fFirstPCR(0.0), fLastPCR(0.0), fHaveSeenFirstPCR(False),
    fPMT_PID(0x10), fVideo_PID(0xE0), // default values
    fParseBufferSize(PARSE_BUFFER_SIZE),
    fParseBufferFrameStart(0), fParseBufferParseEnd(4), fParseBufferDataEnd(0),
    fHeadIndexRecord(NULL), fTailIndexRecord(NULL) {
  fParseBuffer = new unsigned char[fParseBufferSize];
}

MPEG2IFrameIndexFromTransportStream::~MPEG2IFrameIndexFromTransportStream() {
  delete fHeadIndexRecord;
  delete[] fParseBuffer;
}

void MPEG2IFrameIndexFromTransportStream::doGetNextFrame() {
  // Begin by trying to deliver an index record (for an already-parsed frame)
  // to the client:
  if (deliverIndexRecord()) return;

  // No more index records are left to deliver, so try to parse a new frame:
  if (parseFrame()) { // success - try again
    doGetNextFrame();
    return;
  }

  // We need to read some more Transport Stream packets.  Check whether we have room:
  if (fParseBufferSize - fParseBufferDataEnd < TRANSPORT_PACKET_SIZE) {
    // There's no room left.  Compact the buffer, and check again:
    compactParseBuffer();
    if (fParseBufferSize - fParseBufferDataEnd < TRANSPORT_PACKET_SIZE) {
      envir() << "ERROR: parse buffer full; increase MAX_FRAME_SIZE\n";
      // Treat this as if the input source ended:
      handleInputClosure1();
      return;
    }
  }

  // Arrange to read a new Transport Stream packet:
  fInputSource->getNextFrame(fInputBuffer, sizeof fInputBuffer,
			     afterGettingFrame, this,
			     handleInputClosure, this);
}

void MPEG2IFrameIndexFromTransportStream
::afterGettingFrame(void* clientData, unsigned frameSize,
		    unsigned numTruncatedBytes,
		    struct timeval presentationTime,
		    unsigned durationInMicroseconds) {
  MPEG2IFrameIndexFromTransportStream* source
    = (MPEG2IFrameIndexFromTransportStream*)clientData;
  source->afterGettingFrame1(frameSize, numTruncatedBytes,
			     presentationTime, durationInMicroseconds);
}

#define TRANSPORT_SYNC_BYTE 0x47

void MPEG2IFrameIndexFromTransportStream
::afterGettingFrame1(unsigned frameSize,
		     unsigned numTruncatedBytes,
		     struct timeval presentationTime,
		     unsigned durationInMicroseconds) {
  if (frameSize < TRANSPORT_PACKET_SIZE || fInputBuffer[0] != TRANSPORT_SYNC_BYTE) {
    if (fInputBuffer[0] != TRANSPORT_SYNC_BYTE) {
      envir() << "Bad TS sync byte: 0x" << fInputBuffer[0] << "\n";
    }
    // Handle this as if the source ended:
    handleInputClosure1();
    return;
  }

  ++fInputTransportPacketCounter;

  // Figure out how much of this Transport Packet contains PES data:
  u_int8_t adaptation_field_control = (fInputBuffer[3]&0x30)>>4;
  u_int8_t totalHeaderSize
    = adaptation_field_control <= 1 ? 4 : 5 + fInputBuffer[4];
  if ((adaptation_field_control == 2 && totalHeaderSize != TRANSPORT_PACKET_SIZE) ||
      (adaptation_field_control == 3 && totalHeaderSize >= TRANSPORT_PACKET_SIZE)) {
    envir() << "Bad \"adaptation_field_length\": " << fInputBuffer[4] << "\n";
    doGetNextFrame();
    return;
  }

  // Check for a PCR:
  if (totalHeaderSize > 5 && (fInputBuffer[5]&0x10) != 0) {
    // There's a PCR:
    u_int32_t pcrBaseHigh
      = (fInputBuffer[6]<<24)|(fInputBuffer[7]<<16)
      |(fInputBuffer[8]<<8)|fInputBuffer[9];
    float pcr = pcrBaseHigh/45000.0f;
    if ((fInputBuffer[10]&0x80) != 0) pcr += 1/90000.0f; // add in low-bit (if set)
    unsigned short pcrExt = ((fInputBuffer[10]&0x01)<<8) | fInputBuffer[11];
    pcr += pcrExt/27000000.0f;

    if (!fHaveSeenFirstPCR) {
      fFirstPCR = pcr;
      fHaveSeenFirstPCR = True;
    } else if (pcr < fLastPCR) {
      // The PCR timestamp has gone backwards.  Display a warning about this
      // (because it indicates buggy Transport Stream data), and compensate for it.
      envir() << "\nWarning: At about " << fLastPCR-fFirstPCR
	      << " seconds into the file, the PCR timestamp decreased - from "
	      << fLastPCR << " to " << pcr << "\n";
      fFirstPCR -= (fLastPCR - pcr);
    }
    fLastPCR = pcr;
  }

  // Get the PID from the packet, and check for special tables: the PAT and PMT:
  u_int16_t PID = ((fInputBuffer[1]&0x1F)<<8) | fInputBuffer[2];
  if (PID == PAT_PID) {
    analyzePAT(&fInputBuffer[totalHeaderSize], TRANSPORT_PACKET_SIZE-totalHeaderSize);
  } else if (PID == fPMT_PID) {
    analyzePMT(&fInputBuffer[totalHeaderSize], TRANSPORT_PACKET_SIZE-totalHeaderSize);
  }

  // Ignore transport packets for non-video programs,
  // or packets with no data, or packets that duplicate the previous packet:
  u_int8_t continuity_counter = fInputBuffer[3]&0x0F;
  if ((PID != fVideo_PID) ||
      !(adaptation_field_control == 1 || adaptation_field_control == 3) ||
      continuity_counter == fLastContinuityCounter) {
    doGetNextFrame();
    return;
  }
  fLastContinuityCounter = continuity_counter;

  // Also, if this is the start of a PES packet, then skip over the PES header:
  Boolean payload_unit_start_indicator = (fInputBuffer[1]&0x40) != 0;
  if (payload_unit_start_indicator && totalHeaderSize < TRANSPORT_PACKET_SIZE - 8 
      && fInputBuffer[totalHeaderSize] == 0x00 && fInputBuffer[totalHeaderSize+1] == 0x00
      && fInputBuffer[totalHeaderSize+2] == 0x01) {
    u_int8_t PES_header_data_length = fInputBuffer[totalHeaderSize+8];
    totalHeaderSize += 9 + PES_header_data_length;
    if (totalHeaderSize >= TRANSPORT_PACKET_SIZE) {
      envir() << "Unexpectedly large PES header size: " << PES_header_data_length << "\n";
      // Handle this as if the source ended:
      handleInputClosure1();
      return;
    }
  }

  // The remaining data is Video Elementary Stream data.  Add it to our parse buffer:
  unsigned vesSize = TRANSPORT_PACKET_SIZE - totalHeaderSize;
  memmove(&fParseBuffer[fParseBufferDataEnd], &fInputBuffer[totalHeaderSize], vesSize);
  fParseBufferDataEnd += vesSize;

  // And add a new index record noting where it came from:
  addToTail(new IndexRecord(totalHeaderSize, vesSize, fInputTransportPacketCounter,
			    fLastPCR - fFirstPCR));

  // Try again:
  doGetNextFrame();
}

void MPEG2IFrameIndexFromTransportStream::handleInputClosure(void* clientData) {
  MPEG2IFrameIndexFromTransportStream* source
    = (MPEG2IFrameIndexFromTransportStream*)clientData;
  source->handleInputClosure1();
}

#define VIDEO_SEQUENCE_START_CODE 0xB3		// MPEG-1 or 2
#define VISUAL_OBJECT_SEQUENCE_START_CODE 0xB0	// MPEG-4
#define GROUP_START_CODE 0xB8			// MPEG-1 or 2
#define GROUP_VOP_START_CODE 0xB3		// MPEG-4
#define PICTURE_START_CODE 0x00			// MPEG-1 or 2
#define VOP_START_CODE 0xB6			// MPEG-4

void MPEG2IFrameIndexFromTransportStream::handleInputClosure1() {
  if (++fClosureNumber == 1 && fParseBufferDataEnd > fParseBufferFrameStart
      && fParseBufferDataEnd <= fParseBufferSize - 4) {
    // This is the first time we saw EOF, and there's still data remaining to be
    // parsed.  Hack: Append a Picture Header code to the end of the unparsed
    // data, and try again.  This should use up all of the unparsed data.
    fParseBuffer[fParseBufferDataEnd++] = 0;
    fParseBuffer[fParseBufferDataEnd++] = 0;
    fParseBuffer[fParseBufferDataEnd++] = 1;
    fParseBuffer[fParseBufferDataEnd++] = PICTURE_START_CODE;

    // Try again:
    doGetNextFrame();
  } else {
    // Handle closure in the regular way:
    handleClosure();
  }
}

void MPEG2IFrameIndexFromTransportStream
::analyzePAT(unsigned char* pkt, unsigned size) {
  // Get the PMT_PID:
  while (size >= 17) { // The table is large enough
    u_int16_t program_number = (pkt[9]<<8) | pkt[10];
    if (program_number != 0) {
      fPMT_PID = ((pkt[11]&0x1F)<<8) | pkt[12];
      return;
    }

    pkt += 4; size -= 4;
  }
}

void MPEG2IFrameIndexFromTransportStream
::analyzePMT(unsigned char* pkt, unsigned size) {
  // Scan the "elementary_PID"s in the map, until we see the first video stream.

  // First, get the "section_length", to get the table's size:
  u_int16_t section_length = ((pkt[2]&0x0F)<<8) | pkt[3];
  if ((unsigned)(4+section_length) < size) size = (4+section_length);

  // Then, skip any descriptors following the "program_info_length":
  if (size < 22) return; // not enough data
  unsigned program_info_length = ((pkt[11]&0x0F)<<8) | pkt[12];
  pkt += 13; size -= 13;
  if (size < program_info_length) return; // not enough data
  pkt += program_info_length; size -= program_info_length;

  // Look at each ("stream_type","elementary_PID") pair, looking for a video stream:
  while (size >= 9) {
    u_int8_t stream_type = pkt[0];
    u_int16_t elementary_PID = ((pkt[1]&0x1F)<<8) | pkt[2];
    if (stream_type == 1 || stream_type == 2 ||
	stream_type == 0x1B/*H.264 video*/ || stream_type == 0x24/*H.265 video*/) {
      if (stream_type == 0x1B) fIsH264 = True;
      else if (stream_type == 0x24) fIsH265 = True;
      fVideo_PID = elementary_PID;
      return;
    }

    u_int16_t ES_info_length = ((pkt[3]&0x0F)<<8) | pkt[4];
    pkt += 5; size -= 5;
    if (size < ES_info_length) return; // not enough data
    pkt += ES_info_length; size -= ES_info_length;
  }
}

Boolean MPEG2IFrameIndexFromTransportStream::deliverIndexRecord() {
  IndexRecord* head = fHeadIndexRecord;
  if (head == NULL) return False;

  // Check whether the head record has been parsed yet:
  if (head->recordType() == RECORD_UNPARSED) return False;

  // Remove the head record (the one whose data we'll be delivering):
  IndexRecord* next = head->next();
  head->unlink();
  if (next == head) {
    fHeadIndexRecord = fTailIndexRecord = NULL;
  } else {
    fHeadIndexRecord = next;
  }

  if (head->recordType() == RECORD_JUNK) {
    // Don't actually deliver the data to the client:
    delete head;
    // Try to deliver the next record instead:
    return deliverIndexRecord();
  }

  // Deliver data from the head record:
#ifdef DEBUG
  envir() << "delivering: " << *head << "\n";
#endif
  if (fMaxSize < 11) {
    fFrameSize = 0;
  } else {
    fTo[0] = (u_int8_t)(head->recordType());
    fTo[1] = head->startOffset();
    fTo[2] = head->size();
    // Deliver the PCR, as 24 bits (integer part; little endian) + 8 bits (fractional part)
    float pcr = head->pcr();
    unsigned pcr_int = (unsigned)pcr;
    u_int8_t pcr_frac = (u_int8_t)(256*(pcr-pcr_int));
    fTo[3] = (unsigned char)(pcr_int);
    fTo[4] = (unsigned char)(pcr_int>>8);
    fTo[5] = (unsigned char)(pcr_int>>16);
    fTo[6] = (unsigned char)(pcr_frac);
    // Deliver the transport packet number (in little-endian order):
    unsigned long tpn = head->transportPacketNumber();
    fTo[7] = (unsigned char)(tpn);
    fTo[8] = (unsigned char)(tpn>>8);
    fTo[9] = (unsigned char)(tpn>>16);
    fTo[10] = (unsigned char)(tpn>>24);
    fFrameSize = 11;
  }

  // Free the (former) head record (as we're now done with it):
  delete head;

  // Complete delivery to the client:
  afterGetting(this);
  return True;
}

Boolean MPEG2IFrameIndexFromTransportStream::parseFrame() {
  // At this point, we have a queue of >=0 (unparsed) index records, representing
  // the data in the parse buffer from "fParseBufferFrameStart"
  // to "fParseBufferDataEnd".  We now parse through this data, looking for
  // a complete 'frame', where a 'frame', in this case, means:
  // 	for MPEG video: a Video Sequence Header, GOP Header, Picture Header, or Slice
  // 	for H.264 or H.265 video: a NAL unit

  // Inspect the frame's initial 4-byte code, to make sure it starts with a system code:
  if (fParseBufferDataEnd-fParseBufferFrameStart < 4) return False; // not enough data
  unsigned numInitialBadBytes = 0;
  unsigned char const* p = &fParseBuffer[fParseBufferFrameStart];
  if (!(p[0] == 0 && p[1] == 0 && p[2] == 1)) {
    // There's no system code at the beginning.  Parse until we find one:
    if (fParseBufferParseEnd == fParseBufferFrameStart + 4) {
      // Start parsing from the beginning of the frame data:
      fParseBufferParseEnd = fParseBufferFrameStart;
    }
    unsigned char nextCode;
    if (!parseToNextCode(nextCode)) return False;

    numInitialBadBytes = fParseBufferParseEnd - fParseBufferFrameStart;
    fParseBufferFrameStart = fParseBufferParseEnd;
    fParseBufferParseEnd += 4; // skip over the code that we just saw
    p = &fParseBuffer[fParseBufferFrameStart];
  }

  unsigned char curCode = p[3];
  if (fIsH264) curCode &= 0x1F; // nal_unit_type
  else if (fIsH265) curCode = (curCode&0x7E)>>1;

  RecordType curRecordType;
  unsigned char nextCode;
  if (fIsH264) {
    switch (curCode) {
    case 1: // Coded slice of a non-IDR picture
      curRecordType = RECORD_NAL_H264_NON_IFRAME;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 5: // Coded slice of an IDR picture
      curRecordType = RECORD_NAL_H264_IFRAME;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 6: // Supplemental enhancement information (SEI)
      curRecordType = RECORD_NAL_H264_SEI;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 7: // Sequence parameter set (SPS)
      curRecordType = RECORD_NAL_H264_SPS;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 8: // Picture parameter set (PPS)
      curRecordType = RECORD_NAL_H264_PPS;
      if (!parseToNextCode(nextCode)) return False;
      break;
    default:
      curRecordType = RECORD_NAL_H264_OTHER;
      if (!parseToNextCode(nextCode)) return False;
      break;
    }
  } else if (fIsH265) {
    switch (curCode) {
    case 19: // Coded slice segment of an IDR picture
    case 20: // Coded slice segment of an IDR picture
      curRecordType = RECORD_NAL_H265_IFRAME;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 32: // Video parameter set (VPS)
      curRecordType = RECORD_NAL_H265_VPS;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 33: // Sequence parameter set (SPS)
      curRecordType = RECORD_NAL_H265_SPS;
      if (!parseToNextCode(nextCode)) return False;
      break;
    case 34: // Picture parameter set (PPS)
      curRecordType = RECORD_NAL_H265_PPS;
      if (!parseToNextCode(nextCode)) return False;
      break;
    default:
      curRecordType = (curCode <= 31) ? RECORD_NAL_H265_NON_IFRAME : RECORD_NAL_H265_OTHER;
      if (!parseToNextCode(nextCode)) return False;
      break;
    }
  } else { // MPEG-1, 2, or 4
    switch (curCode) {
    case VIDEO_SEQUENCE_START_CODE:
    case VISUAL_OBJECT_SEQUENCE_START_CODE:
      curRecordType = RECORD_VSH;
      while (1) {
	if (!parseToNextCode(nextCode)) return False;
	if (nextCode == GROUP_START_CODE ||
	    nextCode == PICTURE_START_CODE || nextCode == VOP_START_CODE) break;
	fParseBufferParseEnd += 4; // skip over the code that we just saw
      }
      break;
    case GROUP_START_CODE:
      curRecordType = RECORD_GOP;
      while (1) {
	if (!parseToNextCode(nextCode)) return False;
	if (nextCode == PICTURE_START_CODE || nextCode == VOP_START_CODE) break;
	fParseBufferParseEnd += 4; // skip over the code that we just saw
      }
      break;
    default: // picture
      curRecordType = RECORD_PIC_NON_IFRAME; // may get changed to IFRAME later
      while (1) {
        if (!parseToNextCode(nextCode)) return False;
        if (nextCode == VIDEO_SEQUENCE_START_CODE ||
	    nextCode == VISUAL_OBJECT_SEQUENCE_START_CODE ||
	    nextCode == GROUP_START_CODE || nextCode == GROUP_VOP_START_CODE ||
	    nextCode == PICTURE_START_CODE || nextCode == VOP_START_CODE) break;
        fParseBufferParseEnd += 4; // skip over the code that we just saw
      }
      break;
    }
  }

  if (curRecordType == RECORD_PIC_NON_IFRAME) {
    if (curCode == VOP_START_CODE) { // MPEG-4
      if ((fParseBuffer[fParseBufferFrameStart+4]&0xC0) == 0) {
	// This is actually an I-frame.  Note it as such:
	curRecordType = RECORD_PIC_IFRAME;
      }
    } else { // MPEG-1 or 2
      if ((fParseBuffer[fParseBufferFrameStart+5]&0x38) == 0x08) {
	// This is actually an I-frame.  Note it as such:
	curRecordType = RECORD_PIC_IFRAME;
      }
    }
  }

  // There is now a parsed 'frame', from "fParseBufferFrameStart"
  // to "fParseBufferParseEnd". Tag the corresponding index records to note this:
  unsigned frameSize = fParseBufferParseEnd - fParseBufferFrameStart + numInitialBadBytes;
#ifdef DEBUG
  envir() << "parsed " << recordTypeStr[curRecordType] << "; length "
	  << frameSize << "\n";
#endif
  for (IndexRecord* r = fHeadIndexRecord; ; r = r->next()) {
    if (numInitialBadBytes >= r->size()) {
      r->recordType() = RECORD_JUNK;
      numInitialBadBytes -= r->size();
    } else {
      r->recordType() = curRecordType;
    }
    if (r == fHeadIndexRecord) r->setFirstFlag();
    // indicates that this is the first record for this frame

    if (r->size() > frameSize) {
      // This record contains extra data that's not part of the frame.
      // Shorten this record, and move the extra data to a new record
      // that comes afterwards:
      u_int8_t newOffset = r->startOffset() + frameSize;
      u_int8_t newSize = r->size() - frameSize;
      r->size() = frameSize;
#ifdef DEBUG
      envir() << "tagged record (modified): " << *r << "\n";
#endif

      IndexRecord* newRecord
	= new IndexRecord(newOffset, newSize, r->transportPacketNumber(), r->pcr());
      newRecord->addAfter(r);
      if (fTailIndexRecord == r) fTailIndexRecord = newRecord;
#ifdef DEBUG
      envir() << "added extra record: " << *newRecord << "\n";
#endif
    } else {
#ifdef DEBUG
      envir() << "tagged record: " << *r << "\n";
#endif
    }
    frameSize -= r->size();
    if (frameSize == 0) break;
    if (r == fTailIndexRecord) { // this shouldn't happen
      envir() << "!!!!!Internal consistency error!!!!!\n";
      return False;
    }
  }

  // Finally, update our parse state (to skip over the now-parsed data):
  fParseBufferFrameStart = fParseBufferParseEnd;
  fParseBufferParseEnd += 4; // to skip over the next code (that we found)

  return True;
}

Boolean MPEG2IFrameIndexFromTransportStream
::parseToNextCode(unsigned char& nextCode) {
  unsigned char const* p = &fParseBuffer[fParseBufferParseEnd];
  unsigned char const* end = &fParseBuffer[fParseBufferDataEnd];
  while (p <= end-4) {
    if (p[2] > 1) p += 3; // common case (optimized)
    else if (p[2] == 0) ++p;
    else if (p[0] == 0 && p[1] == 0) { // && p[2] == 1
      // We found a code here:
      nextCode = p[3];
      fParseBufferParseEnd = p - &fParseBuffer[0]; // where we've gotten to
      return True;
    } else p += 3;
  }

  fParseBufferParseEnd = p - &fParseBuffer[0]; // where we've gotten to
  return False; // no luck this time
}

void MPEG2IFrameIndexFromTransportStream::compactParseBuffer() {
#ifdef DEBUG
  envir() << "Compacting parse buffer: [" << fParseBufferFrameStart
	  << "," << fParseBufferParseEnd << "," << fParseBufferDataEnd << "]";
#endif
  memmove(&fParseBuffer[0], &fParseBuffer[fParseBufferFrameStart],
	  fParseBufferDataEnd - fParseBufferFrameStart);
  fParseBufferDataEnd -= fParseBufferFrameStart;
  fParseBufferParseEnd -= fParseBufferFrameStart;
  fParseBufferFrameStart = 0;
#ifdef DEBUG
  envir() << "-> [" << fParseBufferFrameStart
	  << "," << fParseBufferParseEnd << "," << fParseBufferDataEnd << "]\n";
#endif
}

void MPEG2IFrameIndexFromTransportStream::addToTail(IndexRecord* newIndexRecord) {
#ifdef DEBUG
  envir() << "adding new: " << *newIndexRecord << "\n";
#endif
  if (fTailIndexRecord == NULL) {
    fHeadIndexRecord = fTailIndexRecord = newIndexRecord;
  } else {
    newIndexRecord->addAfter(fTailIndexRecord);
    fTailIndexRecord = newIndexRecord;
  }
}

////////// IndexRecord implementation //////////

IndexRecord::IndexRecord(u_int8_t startOffset, u_int8_t size,
			 unsigned long transportPacketNumber, float pcr)
  : fNext(this), fPrev(this), fRecordType(RECORD_UNPARSED),
    fStartOffset(startOffset), fSize(size),
    fPCR(pcr), fTransportPacketNumber(transportPacketNumber) {
}

IndexRecord::~IndexRecord() {
  IndexRecord* nextRecord = next();
  unlink();
  if (nextRecord != this) delete nextRecord;
}

void IndexRecord::addAfter(IndexRecord* prev) {
  fNext = prev->fNext;
  fPrev = prev;
  prev->fNext->fPrev = this;
  prev->fNext = this;
}

void IndexRecord::unlink() {
  fNext->fPrev = fPrev;
  fPrev->fNext = fNext;
  fNext = fPrev = this;
}