The VideoLAN Forums

Hello everybody,
I have a question about cpu usage. Namely, when I transcode stream from tv card using h264(x264) encoding cpu is almost all the time on 100% usage. Machine is DualCore on 3GHz with 2GB memory, OS is winXP. I tried to change "threads" parameter but it doesn't change anything.
One of transcode attempts is like this: "venc=x264{keyint=128,idrint=2,cabac=0,bframes=0},vcodec=h264,vb=1000,fps=30,width=640,height=480,threads=2,acodec=mp4a,ab=32,channels= 1,samplerate=44100}"

Is there a way to reduce that cpu usage?
What level of cpu usage is "normal" for h264 encoding using vlc?
Is there a difference using vlc and h264 encoding on windows vs. linux?

Thanks in advance.

Transcoding should always take 100% CPU since VLC tries to convert as fast as possible.

Is there any parameter which can define encoding performance? Something like 'convert slow/medium/fast'?
I mean, it's not possible to have machine running 24x7 with 100% cpu usage ...

when transoding from a file, it should be 100% of CPU
But when transcoding from your tv card, you can reduce your cpu usage by reducing the fps.

As I said, I'm transcoding from tv card and I tried with some standard fps values(30, 25, 24) but cpu usage is always 100%. Right now, I tried with fps=15 but still cpu is lock on 100%.

Is there anything else I can try?

Could you plz report CPU usage with MP4 codec?

ammoun, you meant MPEG4 I think...

ammoun, you meant MPEG4 I think...

Right! Thanks Sébastien Escudier.

With these transcode settings "transcode{vcodec=mpeg4,vb=800,scale=1,acodec=mp4a,ab=128,channels=2,samplerate=44100}" CPU usage is between 75% and 95%. Rarely it goes below 75%, also rarely it goes up(above 95%).

That's very high...
Maybe your input access reads frame from the tv card too fast, and don't limit the fps ?

Sébastien Escudier said:
Maybe your input access reads frame from the tv card too fast

I'm not sure what that means and how I can check or change that?
Also, I tried to define fps using values 24, 25, 30 but that doesn't change anything.

Do you have any idea?

I just tested on linux and it takes 65% of my 2.4Ghz CPU, with mpeg4
But I don't know how the capture of the tv card works on windows...

Thanks, these days I'll try on linux and see if there is any difference.

I am streaming from a TV Card on Ubuntu 10.04 running on Intel Core 2 Duo E8500 3.16Ghz / 6Mb L2 Cache / 2Gb of RAM.
My CPU usage was 165% on average (and load at 2.00). It was so strange, that I had to look up online why the CPU would ever be shown more than 100% load. Seems standard on Linux, if you have more than one CPU or more cores.

I was transcoding with:
It seems that switching from threads=2 to threads=1 lowered the CPU usage in half to ~80%. It still encodes properly and I have no loss of quality.