[x264-devel] Question about x264 real time encoding

[Jason Garrett-Glaser]

> Thanks. Actually when encoding 720P video file using zerolatency +
> veryfast I can get 43fps, while removing sliced-threads I get 81fps.
> Besides,
> I used the version 1510 from x264.nl and the result is 45fps and 82fps. So
> it seems my compiled version is functioning right. My cpu is a E5345 which
> has 2 physical cpu and each have 4 cores. 2.33MHz
>
> I think the throughput difference comes from cpu usage: using
> frame-based threads I can get 66% in the previous experiment, while
> using sliced-based I can get 40%. But I don't know how to improve cpu
> usage and thus further reduce encoding time of one frame in
> sliced-mode. This is critical in real time encoding because if x264 cannot
> encode a frame within 30ms, then there have to be a frame drop.

In tests we have gotten a 1080p frame encoded as fast as 8
milliseconds.  720p should be easy.  Are you running a pre-2.6.32
Linux kernel?  If so, update; the scheduler was bugged, hurting x264.
Is your input decoding/reading off disk/whatever fast enough to feed
x264?

> Another question I thought a lot is how did x264 manage frame based
> threading? If the sequence is IPPPPPPP..., does that mean x264 encode I
> frame first, then use seperate thread to encode the following P s? Then
> how does it handle P referencing P? Or they just all referencing I frame?

http://akuvian.org/src/x264/sliceless_threads.txt

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