[Libav-user] latency of mpegts handling in libavformat

[כרמל מגן]

I am sending and receiving h.264 video on mpeg2-ts over udp.
After noticing some lag, I added code that prints a timestamp and
framenumber after sending and after av_read_frame returns. when comparing
timestamps between frames with the same frame number, there is a ~60 ms
delay (when sending 30 fps). Furthermore, if I stop at a breakpoint and
delay the sending of frame number X, the timestamp of receiving frame number
X-2 corresponds to the time of sending of  X (i.e., the time between
receiving frame number X-3 and  frame number X-2 is longer if I delay the
sending of X longer). The unavoidable conclusion is that av_read_frame *does
not return* with frame X-2 until frame X starts arriving.

Carmel

2011/7/27 Alex Cohn <alexcohn at netvision.net.il>

> On Wed, Jul 27, 2011 at 10:27, כרמל מגן <carmel.work at gmail.com> wrote:
>
>> av_read_frame does not return until the third frame arrives. This
>> introduces 2 frames delay *before* the decoding.
>>
>
> What do you mean "av_read_frame does not return"?
>
> from avformat.h:
>  * This function returns what is stored in the file, and does not validate
>  * that what is there are valid frames for the decoder. It will split what
> is
> ...
>  * @return 0 if OK, < 0 on error or end of file
>
> So, does it return negative number? Or the packet is not a video packet?
> Maybe, you have the first video packet spliced into three network packets?
> Note that the first video frame is large (it is a key frame, naturally). The
> subsequent packet are much much smaller, becasue they encode only delta.
>
> Cheers,
> Alex
>
>
> _______________________________________________
> Libav-user mailing list
> Libav-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/libav-user
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ffmpeg.org/pipermail/libav-user/attachments/20110727/bb8b1576/attachment.html>