x264_64.exe cpu load

[Ennio]

Hi everybody

Using BD Rebuilder as well as multiAVCHD it pops to my attention that, when encoding in 2 pass mode, x264_64.exe loads the CPU about 50% during 1st pass. On the 2nd pass CPU load is 100%.

Is this due to the command-line these appz "give" to x264? Or is it purely a x264 thing itself? I want to use cpu at it's full capacity, also during 1st pass. I am not that familiair with cli, but is there a way to do this?

Thanks in advance

Ennio

[Atak_Snajpera]

add --slow-firstpass to x264 command line

[Selur]

*gig* and here I was trying to think about how to write an explanation why this is happening (bottelnecks, threading, etc.) *gig*
-> @Atak: I really love the simplicity of your answer.

[jagabo]

Run Prime95 or CPU Burn in the background to hog up CPU resources. That will work just as well as using a slow first pass.

[CubDukat]

Not getting full CPU utilization on a first pass is actually normal. If I understand the mechanics of 2-pass encoding, the first pass is just a cursory look to make notes about where to apply compression, then the second pass is the actual compression. Putting more processor power behind a first pass doesn't really have a noticeable effect unless you're going to a substantially lower bitrate than the source material (ex. Blu-Ray to iPod).

You probably already know this, but you should try to look for what gives you the best results with the least hit on system resources.

[jagabo]

The issue is what Selur hinted at: during a fast first pass x264's processing is not the bottleneck. Reading the source file, decompressing it, and any other filtering is the bottleneck. It's like feeding a fire hose with your kitchen faucet. The fire hose may be capable of delivering 1000 gallons a minute but your kitchen faucet can only feed it 2 gallons a minute. So you'll only get 2 gallons a minute out of your fire hose. By forcing a slow first pass in x264 you are making it do more work, but that extra work isn't going to improve its output appreciably. If you really want to squeeze more performance out of the conversion look at what's feeding x264. Or switch to CRF encoding -- which is about the same speed as the second pass of a 2 pass encode, without having to perform the information gathering first pass.

[Ennio]

add --slow-firstpass to x264 command line

How do I do that in both multiAVCHD and BD Rebuilder?

... Or switch to CRF encoding -- which is about the same speed as the second pass of a 2 pass encode, without having to perform the information gathering first pass.

How can I do that in multiAVCHD? I checked the settings but can't find it?


Thanks

Ennio

[jagabo]

I don't use multiAVCHD or BD Rebuilder so can't tell you. But with the command line x264 encoder you set CRF mode with "--crf nn" where nn can be any number from 0 (lossless) to 51 (very poor). Try values around 16 to 20. You must remove the bitrate options when using CRF encoding*. Atak gave you the exact CLI command for the slow first pass option.

* when encoding video you have two basic methods: constant quality or bitrate. With bitrate based encoding you specify the bitrate. You know how big the file will turn out but you don't know what the quality will be. With quality based encoding you specify the quality. You know what the quality will be but you don't know how big the file will turn out.

[Ennio]

... with the command line x264 encoder you set CRF mode with "--crf nn" where nn can be any number from 0 (lossless) to 51 (very poor). Try values around 16 to 20. You must remove the bitrate options when using CRF encoding*. Atak gave you the exact CLI command for the slow first pass option.

Yes, I read about this. The CRF settings are also in Handbrake, where you have to choose between 2 options: CRF with the RF slider or ABR settings. I think I got it.

* when encoding video you have two basic methods: constant quality or bitrate. With bitrate based encoding you specify the bitrate. You know how big the file will turn out but you don't know what the quality will be. With quality based encoding you specify the quality. You know what the quality will be but you don't know how big the file will turn out.

Thanks jagabo.

I will have to get myself familiair with the cli of x264 or x264_64.

Cheers all

Ennio