On 27/05/2011 15:05, Ronald S. Bultje wrote:
Hi Mark,
On Fri, May 27, 2011 at 9:56 AM, Mark Kenna
<[email protected]> wrote:
On 27/05/2011 14:51, Ronald S. Bultje wrote:
On Fri, May 27, 2011 at 9:49 AM, Mark Kenna
<[email protected]> wrote:
I'm having a hard time getting my head around encoding variable frame
rate
containers in LibAV. I have taken the 'output_example.c' program and
modified it to encode to FLV. What I would like to know is how I would
modify the 'output_example.c' program to write variable time stamp values
into the output file. For my project I will be taking a streaming input
source (which will not have time-stamp information) and will need to
create
my own timestamp values (I guess from the delta value between the last
received frame and the current frame?).
I have read that you need to set the time base value to:
c->time_base.num=1;
c->time_base.den=1000;
But I am not sure exactly what I should be setting the encoded packet's
PTS
values to?
This means "each pts value has a fractional unit of 1/1000th", or in
other words, millisecond precision. So if your timestamps are 10ms,
22ms, 38ms, then pts would be 10, 22 and 38.
Ronald
Wow! That was quick - thanks!
So after encoding the frame and calculating what the pts value should be
(based on the delay between the last frame and this one) I would do:
pkt.stream_index= st->index;
pkt.data= video_outbuf;
pkt.size= out_size;
pkt.pts= previousPacketPts + deltaDelay;
/* write the compressed frame in the media file */
ret = av_write_frame(oc,&pkt);
If that makes any sense?
That works, if you're not using B-frames.
If you're using B-frames, I'd suggest using
AVCodecContext->coded_frame->pts as a way to set/get the PTS of
encoded frames before/after encoding. ffmpeg.c uses this also.
Ronald
Hi Ronald
That actually works perfectly!
I set up and start a timer when I get the first frame of video, then
before every encode I do:
frame->pts = _stopWatch->ElapsedMilliseconds;
/* encode the image */
out_size = avcodec_encode_video(c, video_outbuf,
video_outbuf_size, frame);
And as I am not using B-Frames it works perfectly. I have not tried (and
will not try) to use this technique with P-Frames.
Thanks for all your help,
Mark.
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