MPEG2TransportStreamFramer.cpp

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// A filter that passes through (unchanged) chunks that contain an integral number
// of MPEG-2 Transport Stream packets, but returning (in "fDurationInMicroseconds")
// an updated estimate of the time gap between chunks.
// Implementation

#include "MPEG2TransportStreamFramer.hh"
#include <GroupsockHelper.hh> // for "gettimeofday()"

#define TRANSPORT_PACKET_SIZE 188
#define NEW_DURATION_WEIGHT 0.5
  // How much weight to give to the latest duration measurement (must be <= 1)
#define TIME_ADJUSTMENT_FACTOR 0.8
  // A factor by which to adjust the duration estimate to ensure that the overall
  // packet transmission times remains matched with the PCR times (which will be the
  // times that we expect receivers to play the incoming packets).
  // (must be <= 1)
#define MAX_PLAYOUT_BUFFER_DURATION 0.1 // (seconds)


class PIDStatus {
public:
  PIDStatus(double _firstClock, double _firstRealTime)
    : firstClock(_firstClock), lastClock(_firstClock),
      firstRealTime(_firstRealTime), lastRealTime(_firstRealTime),
      lastPacketNum(0) {
  }

  double firstClock, lastClock, firstRealTime, lastRealTime;
  unsigned lastPacketNum;
};



MPEG2TransportStreamFramer* MPEG2TransportStreamFramer
::createNew(UsageEnvironment& env, FramedSource* inputSource) {
  return new MPEG2TransportStreamFramer(env, inputSource);
}

MPEG2TransportStreamFramer
::MPEG2TransportStreamFramer(UsageEnvironment& env, FramedSource* inputSource)
  : FramedFilter(env, inputSource),
    fTSPacketCount(0), fTSPacketDurationEstimate(0.0) {
  fPIDStatusTable = HashTable::create(ONE_WORD_HASH_KEYS);
}

MPEG2TransportStreamFramer::~MPEG2TransportStreamFramer() {
  PIDStatus* pidStatus;
  while ((pidStatus = (PIDStatus*)fPIDStatusTable->RemoveNext()) != NULL) {
    delete pidStatus;
  }
  delete fPIDStatusTable;
}

void MPEG2TransportStreamFramer::doGetNextFrame() {
  // Read directly from our input source into our client's buffer:
  fFrameSize = 0;
  fInputSource->getNextFrame(fTo, fMaxSize,
                             afterGettingFrame, this,
                             FramedSource::handleClosure, this);
}

void MPEG2TransportStreamFramer::doStopGettingFrames() {
  FramedFilter::doStopGettingFrames();
  fTSPacketCount = 0;

  // Clear out the existing PID status table:
  PIDStatus* pidStatus;
  while ((pidStatus = (PIDStatus*)fPIDStatusTable->RemoveNext()) != NULL) {
    delete pidStatus;
  }
}

void MPEG2TransportStreamFramer
::afterGettingFrame(void* clientData, unsigned frameSize,
                    unsigned /*numTruncatedBytes*/,
                    struct timeval presentationTime,
                    unsigned /*durationInMicroseconds*/) {
  MPEG2TransportStreamFramer* framer = (MPEG2TransportStreamFramer*)clientData;
  framer->afterGettingFrame1(frameSize, presentationTime);
}

#define TRANSPORT_SYNC_BYTE 0x47

void MPEG2TransportStreamFramer::afterGettingFrame1(unsigned frameSize,
                                                    struct timeval presentationTime) {
  fFrameSize += frameSize;
  unsigned const numTSPackets = fFrameSize/TRANSPORT_PACKET_SIZE;
  fFrameSize = numTSPackets*TRANSPORT_PACKET_SIZE; // an integral # of TS packets
  if (fFrameSize == 0) {
    // We didn't read a complete TS packet; assume that the input source has closed.
    handleClosure(this);
    return;
  }

  // Make sure the data begins with a sync byte:
  unsigned syncBytePosition;
  for (syncBytePosition = 0; syncBytePosition < fFrameSize; ++syncBytePosition) {
    if (fTo[syncBytePosition] == TRANSPORT_SYNC_BYTE) break;
  }
  if (syncBytePosition == fFrameSize) {
    envir() << "No Transport Stream sync byte in data.";
    handleClosure(this);
    return;
  } else if (syncBytePosition > 0) {
    // There's a sync byte, but not at the start of the data.  Move the good data
    // to the start of the buffer, then read more to fill it up again:
    memmove(fTo, &fTo[syncBytePosition], fFrameSize - syncBytePosition);
    fFrameSize -= syncBytePosition;
    fInputSource->getNextFrame(&fTo[fFrameSize], syncBytePosition,
                               afterGettingFrame, this,
                               FramedSource::handleClosure, this);
    return;
  } // else normal case: the data begins with a sync byte

  fPresentationTime = presentationTime;

  // Scan through the TS packets that we read, and update our estimate of
  // the duration of each packet:
  struct timeval tvNow;
  gettimeofday(&tvNow, NULL);
  double timeNow = tvNow.tv_sec + tvNow.tv_usec/1000000.0;
  for (unsigned i = 0; i < numTSPackets; ++i) {
    updateTSPacketDurationEstimate(&fTo[i*TRANSPORT_PACKET_SIZE], timeNow);
  }

  fDurationInMicroseconds
    = numTSPackets * (unsigned)(fTSPacketDurationEstimate*1000000);

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

void MPEG2TransportStreamFramer
::updateTSPacketDurationEstimate(unsigned char* pkt, double timeNow) {
  // Sanity check: Make sure we start with the sync byte:
  if (pkt[0] != TRANSPORT_SYNC_BYTE) {
    envir() << "Missing sync byte!\n";
    return;
  }

  ++fTSPacketCount;

  // If this packet doesn't contain a PCR, then we're not interested in it:
  u_int8_t const adaptation_field_control = (pkt[3]&0x30)>>4;
  if (adaptation_field_control != 2 && adaptation_field_control != 3) return;
      // there's no adaptation_field

  u_int8_t const adaptation_field_length = pkt[4];
  if (adaptation_field_length == 0) return;

  u_int8_t const discontinuity_indicator = pkt[5]&0x80;
  u_int8_t const pcrFlag = pkt[5]&0x10;
  if (pcrFlag == 0) return; // no PCR

  // There's a PCR.  Get it, and the PID:
  u_int32_t pcrBaseHigh = (pkt[6]<<24)|(pkt[7]<<16)|(pkt[8]<<8)|pkt[9];
  double clock = pcrBaseHigh/45000.0;
  if ((pkt[10]&0x80) != 0) clock += 1/90000.0; // add in low-bit (if set)
  unsigned short pcrExt = ((pkt[10]&0x01)<<8) | pkt[11];
  clock += pcrExt/27000000.0;

  unsigned pid = ((pkt[1]&0x1F)<<8) | pkt[2];

  // Check whether we already have a record of a PCR for this PID:
  PIDStatus* pidStatus = (PIDStatus*)(fPIDStatusTable->Lookup((char*)pid));
  if (pidStatus == NULL) {
    // We're seeing this PID's PCR for the first time:
    pidStatus = new PIDStatus(clock, timeNow);
    fPIDStatusTable->Add((char*)pid, pidStatus);
#ifdef DEBUG_PCR
    fprintf(stderr, "PID 0x%x, FIRST PCR 0x%08x+%d:%03x == %f @ %f, pkt #%lu\n", pid, pcrBaseHigh, pkt[10]>>7, pcrExt, clock, timeNow, fTSPacketCount);
#endif
  } else {
    // We've seen this PID's PCR before; update our per-packet duration estimate:
    double durationPerPacket
      = (clock - pidStatus->lastClock)/(fTSPacketCount - pidStatus->lastPacketNum);
    if (fTSPacketDurationEstimate == 0.0) { // we've just started
      fTSPacketDurationEstimate = durationPerPacket;
    } else if (discontinuity_indicator == 0 && durationPerPacket >= 0.0) {
      fTSPacketDurationEstimate
        = durationPerPacket*NEW_DURATION_WEIGHT
        + fTSPacketDurationEstimate*(1-NEW_DURATION_WEIGHT);

      // Also adjust the duration estimate to try to ensure that the transmission
      // rate matches the playout rate:
      double transmitDuration = timeNow - pidStatus->firstRealTime;
      double playoutDuration = clock - pidStatus->firstClock;
      if (transmitDuration > playoutDuration) {
        fTSPacketDurationEstimate *= TIME_ADJUSTMENT_FACTOR; // reduce estimate
      } else if (transmitDuration + MAX_PLAYOUT_BUFFER_DURATION < playoutDuration) {
        fTSPacketDurationEstimate /= TIME_ADJUSTMENT_FACTOR; // increase estimate
      }
    } else {
      // the PCR has a discontinuity from its previous value; don't use it now,
      // but reset our PCR and real-time values to compensate:
      pidStatus->firstClock = clock;
      pidStatus->firstRealTime = timeNow;
    }
#ifdef DEBUG_PCR
    fprintf(stderr, "PID 0x%x, PCR 0x%08x+%d:%03x == %f @ %f (diffs %f @ %f), pkt #%lu, discon %d => this duration %f, new estimate %f\n", pid, pcrBaseHigh, pkt[10]>>7, pcrExt, clock, timeNow, clock - pidStatus->firstClock, timeNow - pidStatus->firstRealTime, fTSPacketCount, discontinuity_indicator != 0, durationPerPacket, fTSPacketDurationEstimate);
#endif
  }

  pidStatus->lastClock = clock;
  pidStatus->lastRealTime = timeNow;
  pidStatus->lastPacketNum = fTSPacketCount;
}

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