Dear all,
First of all, I would like to thank you all the developers as even if I
am no expert in FFmpeg I have been using it for numerous applications and
your tool is really awesome! Thanks guys.
Some time ago I have been asked to setup a streaming server with the lowest
amount of latency possible from a Firewire camera to another computer. The
video feedback is used for teleoperation so the stream has soft real-time
requirements. I have crawled the internet for a while and I saw various
posts on this topic but sometimes maybe too old to be useful or sometimes a
bit generic. I collected and reviewed the following:
http://fomori.org/blog/?p=1213-This guy has an interesting article, I will
have a trial to reproduce some of his results.
https://trac.ffmpeg.org/wiki/StreamingGuide
http://ffmpeg.gusari.org/viewtopic.php?f=11
<http://ffmpeg.gusari.org/viewtopic.php?f=11&t=2002> &t=2002
and some others.
I ended up setting up a system which looks like the following.
------------ firewire ----------------------- pipe ----------- .ffm
------------ rtsp --------------------
| Camera | ==> | frame grabber | => | ffmpeg | => | ffserver | =>
| ffmpeg/ffplay |
------------ -----------------------
------------ ------------ --------------------
I was unable to use the libdc1394 format to capture the feed from the camera
so I used a previously written program to grab the frames and then pipe the
raw yuv420p frames to ffmpeg.
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.
FFmpeg is launched with this command:
ffmpeg -hide_banner -f rawvideo -pixel_format gray -video_size 1280x960
-framerate 5 -i - -an http://localhost:8080/stream.ffm
and FFserver:
<Feed stream.ffm>
File /tmp/stream.ffm
FileMaxSize 200K
ACL allow 192.168.0.0 192.168.255.255
</Feed>
<Stream XB3-240.h264>
Feed stream.ffm
Format rtp
VideoCodec libx264
PixelFormat yuv420p
VideoFrameRate 4
VideoSize 320x240
AVOptionVideo crf 23
AVOptionVideo profile baseline
#VideoIntraOnly
VideoGopSize 8
NoAudio
AVOptionAudio flags +global_header
</Stream>
A few questions:
- I was unable to find out how to measure latency in every stage of
the stream, is there a clever method to do it different from quick and dirty
solutions as shown in the first link <http://fomori.org/blog/?p=1213> ?
- May you be able to suggest how to reduce latency as much as
possible at OS and ffmpeg/ffserver and network level.
- I would like to stick to H264 but other option may be evaluated
in case they may bring much better results.
Thanks in advance for any help,
Best regards,
Federico Salvioli.
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