[FFmpeg-user] Ultra-low latency streaming

[Moritz Barsnick]

Hi Federico,

On Mon, Feb 08, 2016 at 14:58:31 +0100, Federico Salvioli wrote:
> I was unable to use the libdc1394 format to capture the feed from the camera

Can you elaborate? Is ffmpeg causing problems?

> With this setup I managed to obtain around 3 seconds of latency. It is
> acceptable as the teleoperation happens not at a very low level but I would
> like to reach sub-second latencies. The priority should be given to latency
> and after to bandwidth as normally the streams travels on wifi LAN.

(I don't know how much latency WiFi introduces. You may have to test
with and without to see the effect.)

> ffmpeg -hide_banner -f rawvideo -pixel_format gray -video_size 1280x960 -framerate 5 -i - -an http://localhost:8080/stream.ffm

Could you please show the complete, uncut console output of this
command? It contains valuable information. (Perhaps make it exit after
a few tens of seconds.)

>       VideoFrameRate 4

Does this not resample your captured 5 fps down to 4? Not a really good
idea.

>       VideoSize 320x240

I think you are rescaling to 320x240 from 1280x960. If you capture at a
lower resolution in the first place - assuming your device allows that
- it will save you a lot of processing.

>       VideoGopSize 8

I may be wrong, but I think the GOP size partly determines latency by
itself. At a framerate of 4, you get an I-frame only every two seconds.
Does this perhaps also imply 2 seconds of latency? Not sure. (I may be
wrong, and the fact that you are avoiding B-frames may already
suffice.)

Just my $0.02,
Moritz