| bool Impala::Core::Stream::Lavc::VideoAccessStrategy::PacketTraceMatchesFrame | ( | const PacketTrace & | trace, | |
| int | frameNr | |||
| ) | const [inline, private] |
Checks the packet table to see whether the specified trace matches the packet context for the specified frame.
The matching algorithm used (empirically established) :
Matching is based on packet size, packet flags, file pointer position after reading the packet, and the packet's source stream. If the specified trace contains more than one video stream packet, the first one is not required to match on either size or flags. The same goes for the first but not only non-video packet. File positions need not match exactly, but they may not exceed the next first key frame's post-read file position.
Definition at line 742 of file VideoAccessStrategy.h.
References Impala::Core::Table::TableTem< Col1T, Col2T, Col3T, Col4T, Col5T, Col6T, Col7T, Col8T, Col9T >::Get1(), Impala::Core::Table::TableTem< Col1T, Col2T, Col3T, Col4T, Col5T, Col6T, Col7T, Col8T, Col9T >::Get2(), Impala::Core::Table::TableTem< Col1T, Col2T, Col3T, Col4T, Col5T, Col6T, Col7T, Col8T, Col9T >::Get3(), Impala::Core::Table::TableTem< Col1T, Col2T, Col3T, Col4T, Col5T, Col6T, Col7T, Col8T, Col9T >::Get4(), ILOG_DEBUG, mFrames, mPackets, and Impala::Core::Table::Table::Size().
Referenced by CurrentFrameMatchesFrame().
00743 { 00744 const int nrOfFrames = mFrames->Size(); 00745 if (frameNr < 0 || frameNr >= nrOfFrames) 00746 return false; 00747 00748 //if (!FrameIsKey(frameNr)) 00749 // return false; 00750 00751 const int traceLen = trace.Size(); 00752 00753 int nrOfVideoPackets = 0; 00754 for (int t = 0; t < traceLen; t++) 00755 if (trace.Get4(t)) 00756 nrOfVideoPackets++; 00757 int nrOfNonVideoPackets = traceLen - nrOfVideoPackets; 00758 00759 int packetIdx = mFrames->Get2(frameNr); 00760 for (int t = traceLen - 1; t >= 0; t--) 00761 { 00762 if (packetIdx < 0) 00763 return false; 00764 00765 const int sizeFromPackets = mPackets->Get2(packetIdx); 00766 const int sizeFromTrace = trace.Get1(t); 00767 const int flagsFromPackets = mPackets->Get3(packetIdx); 00768 const int flagsFromTrace = trace.Get2(t); 00769 bool sizeAndFlagsMatch = 00770 (sizeFromPackets == sizeFromTrace && 00771 flagsFromPackets == flagsFromTrace); 00772 00773 if (trace.Get4(t)) // from video stream? 00774 { 00775 if (--nrOfVideoPackets <= 0) 00776 sizeAndFlagsMatch = true; 00777 } 00778 else 00779 if (--nrOfNonVideoPackets <= 0) 00780 sizeAndFlagsMatch = true; 00781 00782 if (!sizeAndFlagsMatch) 00783 { 00784 ILOG_DEBUG("Size and/or flags don't match at trace pos " << t << 00785 " of " << traceLen << " : " << sizeFromPackets << 00786 " vs. " << sizeFromTrace << " ; " << flagsFromPackets << 00787 " vs. " << flagsFromTrace); 00788 return false; 00789 } 00790 00791 packetIdx--; 00792 00793 // SK: trace matching appears not to be trivial; use only last trace entry 00794 break; 00795 } 00796 00797 // test match for post-read file position 00798 packetIdx = mFrames->Get2(frameNr); 00799 const UInt64 postReadPosOfFrame = mPackets->Get4(packetIdx); 00800 const UInt64 lastPosOfTrace = trace.Get3(traceLen - 1); 00801 if (lastPosOfTrace > postReadPosOfFrame) 00802 { 00803 // locate next key frame 00804 int nextKeyFrame = frameNr + 1; 00805 for ( ; nextKeyFrame < nrOfFrames; nextKeyFrame++) 00806 if (mFrames->Get4(nextKeyFrame)) // is key frame? 00807 break; 00808 if (nextKeyFrame >= nrOfFrames) 00809 return true; // assume a match if no more key frames 00810 00811 // check current (post-read) file position against 00812 // post-read-position of next key frame 00813 packetIdx = mFrames->Get2(nextKeyFrame); 00814 const UInt64 nextKeyFramesFilePos = mPackets->Get4(packetIdx); 00815 if (lastPosOfTrace > nextKeyFramesFilePos) 00816 return false; 00817 } 00818 00819 return true; 00820 }
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