[Libav-user] http streaming latency depends on frame rate

[Geek.Song]

do you tune rc_lookahead to zero?

On Wed, Jun 6, 2012 at 2:57 PM, Aleksey Shubin <x.morion.x at gmail.com> wrote:
> Good day to all.
>
> I'm using libav in my application to encode live video to h264, mux it
> in Live Smooth Streaming format and send to IIS Live Smooth Streaming
> publishing point (via http).
>
> I need to achieve quite low latency (<3 seconds) of live video. When
> the video is recorded on regular frame rate (20-30 fps), everything is
> good and latency is even lower. But when I try lower fps values, the
> latency grows. For 5 fps the latency is 5-6 seconds, for 2 fps it is
> 11 seconds and for 1 fps - 21 second.
>
> I've measured time of the encoding of each frame, it is approximately
> 1.5 seconds and didn't changed with fps. Also disabled all buffering
> at the video player side to exclude it. So the problem seems to be
> somewhere at http transfer process (that is performed by libav too).
>
> First I thought that some kind of buffer is used in libav for http
> transfer, and on the lower frame rate it is filled slower, and that's
> the reason of increased latency. But changing video resolution and
> bitrate doesn't affect on latency, though obviously should change
> encoded frame size and so change the buffer filling rate.
>
> Now I'm completely out of ideas what is reason of that latency and how
> to remove it. Does anyone have any suggestions?
>


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