h263plusvideortpsource.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

/**********
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.,
59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
**********/
// "liveMedia"
// Copyright (c) 1996-2004 Live Networks, Inc.  All rights reserved.
// H.263+ Video RTP Sources
// Implementation

#include "H263plusVideoRTPSource.hh"

H263plusVideoRTPSource*
H263plusVideoRTPSource::createNew(UsageEnvironment& env, Groupsock* RTPgs,
				  unsigned char rtpPayloadFormat,
				  unsigned rtpTimestampFrequency) {
  return new H263plusVideoRTPSource(env, RTPgs, rtpPayloadFormat,
				    rtpTimestampFrequency);
}

H263plusVideoRTPSource
::H263plusVideoRTPSource(UsageEnvironment& env, Groupsock* RTPgs,
			 unsigned char rtpPayloadFormat,
			 unsigned rtpTimestampFrequency)
  : MultiFramedRTPSource(env, RTPgs,
			 rtpPayloadFormat, rtpTimestampFrequency) {
}

H263plusVideoRTPSource::~H263plusVideoRTPSource() {
}

Boolean H263plusVideoRTPSource
::processSpecialHeader(BufferedPacket* packet,
                       unsigned& resultSpecialHeaderSize) {
  unsigned char* headerStart = packet->data();
  unsigned packetSize = packet->dataSize();

  // The H.263+ payload header is at least 2 bytes in size.
  // Extract the known fields from the first 2 bytes:
  unsigned expectedHeaderSize = 2;
  if (packetSize < expectedHeaderSize) return False;

  //unsigned char RR = headerStart[0]>>3;
  Boolean P = (headerStart[0]&0x4) != 0;
  Boolean V = (headerStart[0]&0x2) != 0;
  unsigned char PLEN = ((headerStart[0]&0x1)<<5)|(headerStart[1]>>3);
  //unsigned char PEBIT = headerStart[1]&0x7;

  if (V) {
    // There's an extra VRC byte at the end of the header:
    ++expectedHeaderSize;
    if (packetSize < expectedHeaderSize) return False;
  }
  
  if (PLEN > 0) {
    // There's an extra picture header at the end:
    expectedHeaderSize += PLEN;
    if (packetSize < expectedHeaderSize) return False;
  }

  fCurrentPacketBeginsFrame = P;
  if (fCurrentPacketBeginsFrame) {
    fNumSpecialHeaders = fSpecialHeaderBytesLength = 0;
  }

  // Make a copy of the special header bytes, in case a reader
  // can use them:
  unsigned bytesAvailable
    = SPECIAL_HEADER_BUFFER_SIZE - fSpecialHeaderBytesLength - 1;
  if (expectedHeaderSize <= bytesAvailable) {
    fSpecialHeaderBytes[fSpecialHeaderBytesLength++] = expectedHeaderSize;
    for (unsigned i = 0; i < expectedHeaderSize; ++i) {
      fSpecialHeaderBytes[fSpecialHeaderBytesLength++] = headerStart[i];
    }
    fPacketSizes[fNumSpecialHeaders++] = packetSize;
  }

  if (P) {
    // Prepend two zero bytes to the start of the payload proper.
    // Hack: Do this by shrinking this special header by 2 bytes:
    expectedHeaderSize -= 2;
    headerStart[expectedHeaderSize] = 0;
    headerStart[expectedHeaderSize+1] = 0;
  }

  // The RTP "M" (marker) bit indicates the last fragment of a frame:
  fCurrentPacketCompletesFrame = packet->rtpMarkerBit();

  resultSpecialHeaderSize = expectedHeaderSize;
  return True;
}

char const* H263plusVideoRTPSource::MIMEtype() const {
  return "video/H263-1998";
}