[Libav-user] latency of mpegts handling in libavformat

כרמל מגן carmel.work at gmail.com
Mon Jul 25 07:03:45 CEST 2011

I have investigated the matter some more, and it seems that the delay is
exatcly 2 frames (its 80 ms when I use PAL 25 fps video and 66 ms when I
 use NTSC 30 fps video). Furthermore, it appears when sending frames 1,2,3
av_read_frame does not return with frame 1 before I start sending frame 3.
Does anybody have an idea why this might happen and how I can prevent it?

2011/7/19 כרמל מגן <carmel.work at gmail.com>

> Hello
> I have been integrating mpeg2 transport stream support into an application
> I'm developing using libavformat.
> After successfully transmitting my video (h.264 frames encoded by the
> calling application) and receiving it, I did some latency testing.
> To my surprise, I calculated 80 ms between the time that I finished sending
> the frame in one process (av_write_frame returns) until I finish receiving
> it in the second process (av_read_frame returns and the packet contains the
> same frame).
> To identify the frame I used the pts field of the packet. (i.e I printed
> the time when sending together with the pts of the frame, and then the time
> of receiving together with the pts of the frame, and then calculated the
> difference).
> This was tested using multicast transmission between 2 processes on the
> same computer (on two different machines sitting on different networks) so I
> don't believe network latency can account for it.
> Can anybody explain what might be taking all that time and how I can reduce
> it? My application demands very low latency.
> Thanks
> Carmel
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