On Oct 29, 2009, at 4:10 PM, Jean-Daniel Dupas wrote:
What is reordered_opaque for? I presume it helps with reordered
packets, and I see anecdotal evidence that if I want to override
get_buffer, I should set the frame's reordered_opaque to the
current codec pts, but I'm not sure if it's essential.
Currently, in my video decode tasks, I get the pts of the first
video packet, and use that as the pts of the video frame I obtain
(I stay in the decode job until I get a complete video frame). Is
that no longer a valid approach?
It will not work with codec that use frame reordering (H.264 for
example). To reorder the frame, the decoder will bufferize decoded
frames, and so when you call decode_frame with such decoder, the
decoded frame returned may not be the one corresponding to the
packet you pass as argument.
In such cases, packet pts will not match frame pts.
Oh, I think I see what you're saying. So, whatever packets happened to
go into the decoder, at the time it finishes a frame, the frame may or
may not be related to the packet times (depending on what frame
ordering took place)? Is that right?
So I need to get the reordered_opaque value of the frame that got spat
out.
Then, going back a step, I have to also set the reordered_opaque value
of the frame when the buffer is obtained (since I intend to override
get_buffer)? So, presumably, when a frame buffer is required, the
codec's pts is the correct pts of the frame it's going to make?
Have a look at ffplay.c to see how you can properly handle this kind
of movies.
is->video_st->codec->reordered_opaque= pkt->pts;
len1 = avcodec_decode_video2(is->video_st->codec, frame,
&got_picture, pkt);
if ((decoder_reorder_pts || pkt->dts == AV_NOPTS_VALUE) &&
frame->reordered_opaque != AV_NOPTS_VALUE)
pts= frame->reordered_opaque;
else if (pkt->dts != AV_NOPTS_VALUE)
pts= pkt->dts;
else
pts= 0;
pts *= av_q2d(is->video_st->time_base);
I did see that, but wasn't sure what was going on and why. I guess
this system replaces the 'first packet's pts is the frame pts' logic
used in the ffmpeg tutorial.
I just started to use the ffmpeg-mt branch, if that matters, and I
did add:
#ifdef AVCODEC_HAS_REORDERED_OPAQUE
// take over pts for this frame to have it reordered
pic->reordered_opaque = c->reordered_opaque;
#endif
To my buffer callback.
Regards,
Bruce Wheaton
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-- Jean-Daniel
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