liveMedia/H264VideoStreamDiscreteFramer.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) 1996-2013 Live Networks, Inc.  All rights reserved.
// A simplified version of "H264VideoStreamFramer" 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
// "H264VideoStreamFramer".
// Implementation

#include "H264VideoStreamDiscreteFramer.hh"

H264VideoStreamDiscreteFramer*
H264VideoStreamDiscreteFramer::createNew(UsageEnvironment& env, FramedSource* inputSource) {
  // Need to add source type checking here???  #####
  return new H264VideoStreamDiscreteFramer(env, inputSource);
}

H264VideoStreamDiscreteFramer
::H264VideoStreamDiscreteFramer(UsageEnvironment& env, FramedSource* inputSource)
  : H264VideoStreamFramer(env, inputSource, False/*don't create a parser*/, False) {
}

H264VideoStreamDiscreteFramer::~H264VideoStreamDiscreteFramer() {
}

void H264VideoStreamDiscreteFramer::doGetNextFrame() {
  // Arrange to read data (which should be a complete H.264 NAL unit)
  // 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 H264VideoStreamDiscreteFramer
::afterGettingFrame(void* clientData, unsigned frameSize,
                    unsigned numTruncatedBytes,
                    struct timeval presentationTime,
                    unsigned durationInMicroseconds) {
  H264VideoStreamDiscreteFramer* source = (H264VideoStreamDiscreteFramer*)clientData;
  source->afterGettingFrame1(frameSize, numTruncatedBytes, presentationTime, durationInMicroseconds);
}

void H264VideoStreamDiscreteFramer
::afterGettingFrame1(unsigned frameSize, unsigned numTruncatedBytes,
                     struct timeval presentationTime,
                     unsigned durationInMicroseconds) {
  // Get the "nal_unit_type", to see if this NAL unit is one that we want to save a copy of:
  u_int8_t nal_unit_type = frameSize == 0 ? 0xFF : fTo[0]&0x1F;

  // Check for a (likely) common error: NAL units that (erroneously) begin with a 0x00000001 or 0x000001 'start code'
  //     (Those start codes should only be in byte-stream data; *not* data that consists of discrete NAL units.)
  //     Once again, to be clear: The NAL units that you feed to a "H264VideoStreamDiscreteFramer" MUST NOT include start codes.
  if (nal_unit_type == 0) {
    if (frameSize >= 4 && fTo[0] == 0 && fTo[1] == 0 && ((fTo[2] == 0 && fTo[3] == 1) || fTo[2] == 1)) {
      envir() << "H264VideoStreamDiscreteFramer error: MPEG 'start code' seen in the input\n";
    } else {
      envir() << "Warning: Invalid 'nal_unit_type': 0\n";
    }
  } else if (nal_unit_type == 7) { // Sequence parameter set (SPS)
    saveCopyOfSPS(fTo, frameSize);
  } else if (nal_unit_type == 8) { // Picture parameter set (PPS)
    saveCopyOfPPS(fTo, frameSize);
  }

  // Next, check whether this NAL unit ends the current 'access unit' (basically, a video frame).  Unfortunately, we can't do this
  // reliably, because we don't yet know anything about the *next* NAL unit that we'll see.  So, we guess this as best as we can,
  // by assuming that if this NAL unit is a VCL NAL unit, then it ends the current 'access unit'.
  Boolean const isVCL = nal_unit_type <= 5 && nal_unit_type > 0; // Would need to include type 20 for SVC and MVC #####
  if (isVCL) fPictureEndMarker = True;

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

---