[Libav-user] Fix CBR output for IP multicasting video

[Dang Duc Hung]

Hi All.

I’m using ffmpeg for transcoding live ip multicasting video on server linux Centos 5.9 OS. This is my ffmpeg command

ffmpeg -i "udp:// x.x.x.x:6000?fifo_size=1000000&overrun_nonfatal=1&timeout=1000000" -filter:v yadif=0:-1:1 -vcodec libx264 -vprofile main -level 30 -tune zerolatency -pass 1 -b:v 900k -minrate 900k -maxrate 900k -bufsize 900k -x264opts nal_hrd=cbr:rc_lookahead=40:interlaced=1:scenecut=0:cabac=1:keyint=120:deblock=0,0:aud=1:qpmin=16:qpmax=51:qpstep=10:ref=2:mixed-refs=1:subme=9:me=esa:chroma_me=0:merange=64:8x8dct=0:fast_pskip=0:chroma_qp_offset=0:trellis=2:psy=0:bframes=0:weightp=2:sliced_threads -s:v 720x576 -r:v 25 -force_key_frames 'expr:gte(t,n_forced*3)' -threads 0 -acodec aac -strict -2 -ac 1 -ar 32000 -b:a 32k -filter:a volume=1 -f mpegts -muxrate 1400k udp://x.x.x.x:6000?pkt_size=1316

 

My output video is for broadcasting so I have to configure CBR video output by feature –muxrate. But when I watch this stream on VLC the bitrate change very much not constant. The null packet is very high to force cbr mpeg2ts output.

Description: cid:image005.jpg at 01CFBB26.63925700

 

I also measure IP output video by HST3000 JDSU equipment and I see the measurement result is very bad as images.

The PCR Jitter, IGMP Latency, Jitter Max which is not good as measurement standard by JDSU

Description: cid:image006.jpg at 01CFBB26.63925700

Description: cid:image008.jpg at 01CFBB26.63925700Description: cid:image010.jpg at 01CFBB26.63925700Description: cid:image015.jpg at 01CFBB26.63925700

 

I try many way to change the ffmpeg command but not successful. The bitrate changes sometime > 1400kbps a lot. I think the problem may be the bitrate not constant. I have heard to change the muxrate output is CBR, it had to be change the code C mpegtsenc.c in  <http://ffmpeg.org/libavformat.html> libavformat library to new patch.

So could you help me fix this problem and make the measurment result is better.

Thank you so much.

 

Best Regards

Đặng Đức Hưng

 

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