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FFMPEG Plugin: Fix video start_time generation.

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- Ensure that start times are increased monotonically for video formats that
  contain B-frames, too, as expected by the BMediaDecoders.
  Previously start times were returned that seemed to go back in time for
  videos containing B-frames.
  Tested with resolutionchange.mpg (\see http://samples.ffmpeg.org/MPEG2)
  Note: Even though start times aren't going back in time anymore there are
  times where two consecutive start times are equal. This would need more
  research once this exposes a bug in a real application. Further more this
  might seem like a new bug, but before this commit the equal start times would
  have simply some different start time[s] in between. So at most this is the
  same bug just wearing new clothes :)

- Documentation updated accordingly.
This commit is contained in:
Colin Günther
2014-08-10 14:51:15 +02:00
parent ed9de7dfca
commit 676721d267
1 changed files with 16 additions and 12 deletions
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src/add-ons/media/plugins/ffmpeg/AVFormatReader.cpp
+16 -12
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@@ -701,18 +701,22 @@ StreamBase::GetNextChunk(const void** chunkBuffer,
mediaHeader->destination = -1; mediaHeader->destination = -1;
mediaHeader->time_source = -1; mediaHeader->time_source = -1;
mediaHeader->size_used = fPacket.size; mediaHeader->size_used = fPacket.size;
if (fPacket.pts != kNoPTSValue) {
//TRACE(" PTS: %lld (time_base.num: %d, .den: %d), stream DTS: %lld\n", // FFmpeg recommends to use the decoding time stamps as primary source
//fPacket.pts, fStream->time_base.num, fStream->time_base.den, // for presentation time stamps, especially for video formats that are
//fStream->cur_dts); // using frame reordering. More over this way it is ensured that the
mediaHeader->start_time = _ConvertFromStreamTimeBase(fPacket.pts); // returned start times are ordered in a monotonically increasing time
} else { // series (even for videos that contain B-frames).
//TRACE(" PTS (stream): %lld (time_base.num: %d, .den: %d), stream DTS: %lld\n", // \see http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavformat/avformat.h;h=1e8a6294890d580cd9ebc684eaf4ce57c8413bd8;hb=9153b33a742c4e2a85ff6230aea0e75f5a8b26c2#l1623
//lastStreamDTS, fStream->time_base.num, fStream->time_base.den, bigtime_t presentationTimeStamp;
//fStream->cur_dts); if (fPacket.dts != kNoPTSValue)
mediaHeader->start_time presentationTimeStamp = fPacket.dts;
= _ConvertFromStreamTimeBase(lastStreamDTS); else if (fPacket.pts != kNoPTSValue)
} presentationTimeStamp = fPacket.pts;
else
presentationTimeStamp = lastStreamDTS;
mediaHeader->start_time = _ConvertFromStreamTimeBase(presentationTimeStamp);
mediaHeader->file_pos = fPacket.pos; mediaHeader->file_pos = fPacket.pos;
mediaHeader->data_offset = 0; mediaHeader->data_offset = 0;
switch (mediaHeader->type) { switch (mediaHeader->type) {