optimum amount of cores?

[gahz]

is there such a thing? can i just keep adding more cores to increase fps or will i bottleneck somewhere? only asking because i will be building a new computer that will do nothing but transcode.

right now i run 1 job through 4 cores and i peg the cpu meter at 100%. i tried spliting up jobs (tried between 2-4 jobs) between cores and that didnt speed things up any. i got the best results from 1 job >> 4 cores.

[Soichiro]

At some point you will hit a bottleneck, most likely in hard drive speed or in threadability (either from encoding settings or from avisynth processing or something similar). However, I couldn't tell you what that optimal number of cores is. I have a quad core and x264 seems to use all 4 CPU cores at 100% unless I'm doing something crazy in Avisynth like resizing from 1080p to 480p. So really it mostly depends on how much processing you're going to do on your videos while transcoding them.

[gahz]

so if i wasnt doing anything crazy jumping to 24 cores would speed things up? i use ssd's in raid 0 if that means anything.

[Soichiro]

Theoretically. Of course, threading efficiency does go down as you add more cores, and at some point you will hit a bottleneck somewhere, but whether or not you'll hit that bottleneck by 24 cores, I couldn't say. Of course with SSDs, you shouldn't have to worry about a hard drive bottleneck so much, so your bottleneck will probably end up being decoding speed (which is usually single threaded).

Of course, since you can always run more than one encode at once if one encode doesn't saturate 24 cores, it's not such a bad idea either way to have that many cores.

[mariush]

I'd say it also depends on the encoding settings you use - with placebo you'd probably use even 48 cores easily (4 x 12 core (http://www.acmemicro.com/estore/ShowProduct.aspx?pid=7930) amd processors springs to mind)...

[gahz]

@mariush - yes i saw the amd 12 cores the other day and decided to build a computer using them for the sole purpose of encoding stuff.

@soichiro - i've read somewhere that decoding is single threaded but it sounds to be a fast process since 4 cores still gets loaded up nice and well. i'm really not sure though as i dont have a way to test out more than 4 cores right now.

[Blue_MiSfit]

Decoding is not necessarily single threaded, depending on which decoder you use ;)

ffmpeg-mt in ffdshow / special builds of ffms2, Divx h.264, CoreAVC etc are all extremely fast, multithreaded decoders. There are equivalents for MPEG-2, and other popular formats.

Moar cores are always better ;)

Derek

[Audionut]

Is b-adapt 2 still not mt friendly? Or did that change somewhere I missed.

[nurbs]

Frametype decision runs in a seperate thread now, but it isn't multithreaded so with lots of b-frames it's still a potential bottleneck.

[ajp_anton]

Is b-adapt 2 still not mt friendly? Or did that change somewhere I missed.

b-adapt 1 isn't either, but it's so fast it doesn't really matter unless you use like preset ultrafast.