Well if you are reading from a file, you control the rate at which you
read. So you could stick a pause for say, 100ms somewhere, to throttle
yourself back to 10fps. If you are reading from a network stream going
at full speed, you'll have to drop some frames. You can't play it in
slow-motion, since that would require keeping a potentially infinitely
growing buffer of backlogged frames. So it will require some creativity
to know when to drop and when to keep, to get approximately the correct
framerate. This stackoverflow post gave me some inspiration, when I was
thinking about this:
http://stackoverflow.com/questions/667508/whats-a-good-rate-limiting-algorithm
Andy
On 12/19/2011 8:11 PM, Yingzhou Zhang wrote:
Thanks for your reply.By "control frame rate" I meant,say,the video file
itself is 25fps, and I wanna play the video with the speed of 10frame/s.
Cheers
2011/12/20 Michael Chisholm<[email protected]>
I've struggled myself with this. There are a lot more framerate-related
fields than that lying around. The ones I know of (in ffmpeg 0.6.3) are
(stream=AVStream, cc=AVCodecContext):
stream->time_base
stream->r_frame_rate
stream->avg_frame_rate
cc->time_base
cc->ticks_per_frame
(you'd think you could maybe derive framerate from the last) I am no
expert, but my guess is that not all containers contain a framerate field
somewhere for tools to read. So libav* tries to estimate one from timing
information. E.g. in my app I can read from a udp multicast network
stream, and even for the same stream, each time I run the app, it shows a
slightly different framerate (as shown by dump_format). Maybe because it
sees a different subsequence of timestamps, or the relative distribution in
time of those timestamps might be slightly different, ... I don't know. In
my app, I settled on stream->avg_frame_rate for my purposes.
As far as controlling it, I'm not sure what you mean... did you just want
to decode at the frame rate of the stream, or somehow manipulate the the
video to change its framerate?
Andy
On 12/19/2011 1:25 AM, Yingzhou Zhang wrote:
hey there.
I have googled a little bit,found 2 way
1:AVFormatContext->streams->**time_base.num/den?
2:AVCodecContext-> streams->r_frame_rate?
However the output of the 2 ways are not the same??
Could you tell me what is the exact way to get frame_rate and how to
control it when decoding video?
Thanks a lot
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