liveMedia/MPEGVideoStreamParser.hh

/**********
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.
// An abstract parser for MPEG video streams
// C++ header

#ifndef _MPEG_VIDEO_STREAM_PARSER_HH
#define _MPEG_VIDEO_STREAM_PARSER_HH

#ifndef _STREAM_PARSER_HH
#include "StreamParser.hh"
#endif
#ifndef _MPEG_VIDEO_STREAM_FRAMER_HH
#include "MPEGVideoStreamFramer.hh"
#endif

////////// MPEGVideoStreamParser definition //////////

class MPEGVideoStreamParser: public StreamParser {
public:
  MPEGVideoStreamParser(MPEGVideoStreamFramer* usingSource,
			FramedSource* inputSource);
  virtual ~MPEGVideoStreamParser();

public:
  void registerReadInterest(unsigned char* to, unsigned maxSize);

  virtual unsigned parse() = 0;
      // returns the size of the frame that was acquired, or 0 if none was
      // The number of truncated bytes (if any) is given by:
  unsigned numTruncatedBytes() const { return fNumTruncatedBytes; }

protected:
  void setParseState() {
    fSavedTo = fTo;
    fSavedNumTruncatedBytes = fNumTruncatedBytes;
    saveParserState();
  }

  // Record "byte" in the current output frame:
  void saveByte(u_int8_t byte) {
    if (fTo >= fLimit) { // there's no space left
      ++fNumTruncatedBytes;
      return;
    }

    *fTo++ = byte;
  }

  void save4Bytes(u_int32_t word) {
    if (fTo+4 > fLimit) { // there's no space left
      fNumTruncatedBytes += 4;
      return;
    }

    *fTo++ = word>>24; *fTo++ = word>>16; *fTo++ = word>>8; *fTo++ = word;
  }

  // Save data until we see a sync word (0x000001xx):
  void saveToNextCode(u_int32_t& curWord) {
    saveByte(curWord>>24);
    curWord = (curWord<<8)|get1Byte();
    while ((curWord&0xFFFFFF00) != 0x00000100) {
      if ((unsigned)(curWord&0xFF) > 1) {
	// a sync word definitely doesn't begin anywhere in "curWord"
	save4Bytes(curWord);
	curWord = get4Bytes();
      } else {
	// a sync word might begin in "curWord", although not at its start
	saveByte(curWord>>24);
	unsigned char newByte = get1Byte();
	curWord = (curWord<<8)|newByte;
      }
    }
  }

  // Skip data until we see a sync word (0x000001xx):
  void skipToNextCode(u_int32_t& curWord) {
    curWord = (curWord<<8)|get1Byte();
    while ((curWord&0xFFFFFF00) != 0x00000100) {
      if ((unsigned)(curWord&0xFF) > 1) {
	// a sync word definitely doesn't begin anywhere in "curWord"
	curWord = get4Bytes();
      } else {
	// a sync word might begin in "curWord", although not at its start
	unsigned char newByte = get1Byte();
	curWord = (curWord<<8)|newByte;
      }
    }
  }

protected:
  MPEGVideoStreamFramer* fUsingSource;

  // state of the frame that's currently being read:
  unsigned char* fStartOfFrame;
  unsigned char* fTo;
  unsigned char* fLimit;
  unsigned fNumTruncatedBytes;
  unsigned curFrameSize() { return fTo - fStartOfFrame; }
  unsigned char* fSavedTo;
  unsigned fSavedNumTruncatedBytes;

private: // redefined virtual functions
  virtual void restoreSavedParserState();
};

#endif