[FFmpeg-user] How to optimize transcoding cpu usage

[Rala Wa]

Hi,


I am currently trying to transcode an udp TS stream which contains 1 video stream and 4 audio streams.

I'm using this command line:

ffmpeg -i "udp://239.255.0.10:1234?fifo_size=1000000" \
    -map 0:0 -codec:v libx264 -s 1280x720 -profile:v baseline -preset:v superfast -g 125 -vb 1500k -map 0:1 -codec:a aac -ab 64000 -ar 48000 -ac 2 -strict experimental -f flv rtmp://host/1/720p \
    -map 0:0 -codec:v libx264 -s 800x450 -profile:v baseline -preset:v superfast -g 125 -vb 800k -map 0:1 -codec:a aac -ab 64000 -ar 48000 -ac 2 -strict experimental -f flv rtmp://host/1/450p \
    -map 0:0 -codec:v libx264 -s 384x216 -profile:v baseline -preset:v superfast -g 125 -vb 300k -map 0:1 -codec:a aac -ab 64000 -ar 48000 -ac 2 -strict experimental -f flv rtmp://host/1/216p \
    -map 0:0 -codec:v libx264 -s 1280x720 -profile:v baseline -preset:v superfast -g 125 -vb 1500k -map 0:2 -codec:a aac -ab 64000 -ar 48000 -ac 2 -strict experimental -f flv rtmp://host/2/720p \
    -map 0:0 -codec:v libx264 -s 800x450 -profile:v baseline -preset:v superfast -g 125 -vb 800k -map 0:2 -codec:a aac -ab 64000 -ar 48000 -ac 2 -strict experimental -f flv rtmp://host/2/450p \
    -map 0:0 -codec:v libx264 -s 384x216 -profile:v baseline -preset:v superfast -g 125 -vb 300k -map 0:2 -codec:a aac -ab 64000 -ar 48000 -ac 2 -strict experimental -f flv rtmp://host/2/216p
    

With this command line I encode 6 streams, 3 quality for 2 langs.
In this command line I, for example, transcode two times the 1280x720 video resolution which I think is not optimized.

Can you tell me, if it is possible to encode only one time the video and add different languages to this video?

In fact, to optimize cpu usage I would like to encode only once each video resolution

          ---- 1280x720 ------> 3 outputs with audio 0:1, 0:2, 0:3 ...
         |
TS input --------- 800x450 -------> 3 outputs with audio 0:1, 0:2, 0:3 ...
         |
         ----- 384x216 ------> 2 output with audio 0:1, 0:2, 0:3 ...

I am also surprised by the cpu usage of this command line. With a 8 cores X3450, this command line use 30% on all cores. When I add 3 outputs the cpu usage increase slightly but ffmpeg is not able to do 25 fps transcoding and then I see buffering on the output streams. I tried to nice ffmpeg but It is not better. I hoped to encode more streams with this CPU. 

  
Regards,