liveMedia/MPEG4VideoStreamDiscreteFramer.cpp

Go to the documentation of this file.

/**********
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 2.1 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) 1996-2012 Live Networks, Inc.  All rights reserved.
// A simplified version of "MPEG4VideoStreamFramer" that takes only complete,
// discrete frames (rather than an arbitrary byte stream) as input.
// This avoids the parsing and data copying overhead of the full
// "MPEG4VideoStreamFramer".
// Implementation

#include "MPEG4VideoStreamDiscreteFramer.hh"

MPEG4VideoStreamDiscreteFramer*
MPEG4VideoStreamDiscreteFramer::createNew(UsageEnvironment& env,
                                  FramedSource* inputSource) {
  // Need to add source type checking here???  #####
  return new MPEG4VideoStreamDiscreteFramer(env, inputSource);
}

MPEG4VideoStreamDiscreteFramer
::MPEG4VideoStreamDiscreteFramer(UsageEnvironment& env,
                                 FramedSource* inputSource)
  : MPEG4VideoStreamFramer(env, inputSource, False/*don't create a parser*/),
    vop_time_increment_resolution(0), fNumVTIRBits(0),
    fLastNonBFrameVop_time_increment(0) {
  fLastNonBFramePresentationTime.tv_sec = 0;
  fLastNonBFramePresentationTime.tv_usec = 0;
}

MPEG4VideoStreamDiscreteFramer::~MPEG4VideoStreamDiscreteFramer() {
}

void MPEG4VideoStreamDiscreteFramer::doGetNextFrame() {
  // Arrange to read data (which should be a complete MPEG-4 video frame)
  // from our data source, directly into the client's input buffer.
  // After reading this, we'll do some parsing on the frame.
  fInputSource->getNextFrame(fTo, fMaxSize,
                             afterGettingFrame, this,
                             FramedSource::handleClosure, this);
}

void MPEG4VideoStreamDiscreteFramer
::afterGettingFrame(void* clientData, unsigned frameSize,
                    unsigned numTruncatedBytes,
                    struct timeval presentationTime,
                    unsigned durationInMicroseconds) {
  MPEG4VideoStreamDiscreteFramer* source = (MPEG4VideoStreamDiscreteFramer*)clientData;
  source->afterGettingFrame1(frameSize, numTruncatedBytes,
                             presentationTime, durationInMicroseconds);
}

void MPEG4VideoStreamDiscreteFramer
::afterGettingFrame1(unsigned frameSize, unsigned numTruncatedBytes,
                     struct timeval presentationTime,
                     unsigned durationInMicroseconds) {
  // Check that the first 4 bytes are a system code:
  if (frameSize >= 4 && fTo[0] == 0 && fTo[1] == 0 && fTo[2] == 1) {
    fPictureEndMarker = True; // Assume that we have a complete 'picture' here
    unsigned i = 3;
    if (fTo[i] == 0xB0) { // VISUAL_OBJECT_SEQUENCE_START_CODE
      // The next byte is the "profile_and_level_indication":
      if (frameSize >= 5) fProfileAndLevelIndication = fTo[4];

      // The start of this frame - up to the first GROUP_VOP_START_CODE
      // or VOP_START_CODE - is stream configuration information.  Save this:
      for (i = 7; i < frameSize; ++i) {
        if ((fTo[i] == 0xB3 /*GROUP_VOP_START_CODE*/ ||
             fTo[i] == 0xB6 /*VOP_START_CODE*/)
            && fTo[i-1] == 1 && fTo[i-2] == 0 && fTo[i-3] == 0) {
          break; // The configuration information ends here
        }
      }
      fNumConfigBytes = i < frameSize ? i-3 : frameSize;
      delete[] fConfigBytes; fConfigBytes = new unsigned char[fNumConfigBytes];
      for (unsigned j = 0; j < fNumConfigBytes; ++j) fConfigBytes[j] = fTo[j];

      // This information (should) also contain a VOL header, which we need
      // to analyze, to get "vop_time_increment_resolution" (which we need
      // - along with "vop_time_increment" - in order to generate accurate
      // presentation times for "B" frames).
      analyzeVOLHeader();
    }

    if (i < frameSize) {
      u_int8_t nextCode = fTo[i];

      if (nextCode == 0xB3 /*GROUP_VOP_START_CODE*/) {
        // Skip to the following VOP_START_CODE (if any):
        for (i += 4; i < frameSize; ++i) {
          if (fTo[i] == 0xB6 /*VOP_START_CODE*/
              && fTo[i-1] == 1 && fTo[i-2] == 0 && fTo[i-3] == 0) {
            nextCode = fTo[i];
            break;
          }
        }
      }

      if (nextCode == 0xB6 /*VOP_START_CODE*/ && i+5 < frameSize) {
        ++i;

        // Get the "vop_coding_type" from the next byte:
        u_int8_t nextByte = fTo[i++];
        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
          = (fTo[i]<<24)|(fTo[i+1]<<16)|(fTo[i+2]<<8)|fTo[i+3];
        i += 4;
        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 >>= 2;

        // Then, get the "vop_time_increment".
        unsigned vop_time_increment = 0;
        // First, make sure we have enough bits left for this:
        if ((mask>>(fNumVTIRBits-1)) != 0) {
          for (unsigned i = 0; i < fNumVTIRBits; ++i) {
            vop_time_increment |= timeInfo&mask;
            mask >>= 1;
          }
          while (mask != 0) {
            vop_time_increment >>= 1;
            mask >>= 1;
          }
        }

        // If this is a "B" frame, then we have to tweak "presentationTime":
        if (vop_coding_type == 2/*B*/
            && (fLastNonBFramePresentationTime.tv_usec > 0 ||
                fLastNonBFramePresentationTime.tv_sec > 0)) {
          int timeIncrement
            = fLastNonBFrameVop_time_increment - vop_time_increment;
          if (timeIncrement<0) timeIncrement += vop_time_increment_resolution;
          unsigned const MILLION = 1000000;
          double usIncrement = vop_time_increment_resolution == 0 ? 0.0
            : ((double)timeIncrement*MILLION)/vop_time_increment_resolution;
          unsigned secondsToSubtract = (unsigned)(usIncrement/MILLION);
          unsigned uSecondsToSubtract = ((unsigned)usIncrement)%MILLION;

          presentationTime = fLastNonBFramePresentationTime;
          if ((unsigned)presentationTime.tv_usec < uSecondsToSubtract) {
            presentationTime.tv_usec += MILLION;
            if (presentationTime.tv_sec > 0) --presentationTime.tv_sec;
          }
          presentationTime.tv_usec -= uSecondsToSubtract;
          if ((unsigned)presentationTime.tv_sec > secondsToSubtract) {
            presentationTime.tv_sec -= secondsToSubtract;
          } else {
            presentationTime.tv_sec = presentationTime.tv_usec = 0;
          }
        } else {
          fLastNonBFramePresentationTime = presentationTime;
          fLastNonBFrameVop_time_increment = vop_time_increment;
        }
      }
    }
  }

  // Complete delivery to the client:
  fFrameSize = frameSize;
  fNumTruncatedBytes = numTruncatedBytes;
  fPresentationTime = presentationTime;
  fDurationInMicroseconds = durationInMicroseconds;
  afterGetting(this);
}

Boolean MPEG4VideoStreamDiscreteFramer::getNextFrameBit(u_int8_t& result) {
  if (fNumBitsSeenSoFar/8 >= fNumConfigBytes) return False;

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

Boolean MPEG4VideoStreamDiscreteFramer::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 MPEG4VideoStreamDiscreteFramer::analyzeVOLHeader() {
  // Begin by moving to the VOL header:
  unsigned i;
  for (i = 3; i < fNumConfigBytes; ++i) {
    if (fConfigBytes[i] >= 0x20 && fConfigBytes[i] <= 0x2F
        && fConfigBytes[i-1] == 1
        && fConfigBytes[i-2] == 0 && fConfigBytes[i-3] == 0) {
      ++i;
      break;
    }
  }

  fNumBitsSeenSoFar = 8*i + 9;
  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) break; // sanity check

    if (!getNextFrameBits(16, vop_time_increment_resolution)) break;
    if (vop_time_increment_resolution == 0) break; // shouldn't happen

    // Compute how many bits are necessary to represent this:
    fNumVTIRBits = 0;
    for (unsigned test = vop_time_increment_resolution; test>0; test /= 2) {
      ++fNumVTIRBits;
    }
  } while (0);
}

---