H.264, OpenCL & 2 pass

Bug report and feature request
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Megatron
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H.264, OpenCL & 2 pass

Post by Megatron » Tue Sep 08, 2015 5:29 am

x64 Version 0.8.34 build 5716

The second pass fails to utilize the GPU. I saw the GPU being utilized in the first pass but it was just cpu power in 2nd pass. I had slow preset and ticked use opencl if available. The rest was default AFAIK.

Am I using poor encoding choices or something?
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saikat007saha
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Re: H.264, OpenCL & 2 pass

Post by saikat007saha » Sat Dec 05, 2015 12:51 am

Why is it not possible to use multi-pass crf in Mediacoder ?

I mean I want to use the first pass to determine the bitrate which will be
automatically used as the bitrate for 2nd encode.

When I tick multipass crf option in the 2 pass rate mode,
the process seems to be doing fine but the bitrate used for the 2nd encode is
always the same (irrespective of the crf value) and the one that is set in the bitrate value box.

I am attaching images below with red rectangles for the options I think
responsible for this behaviour.

Image
Image

flagpole
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Re: H.264, OpenCL & 2 pass

Post by flagpole » Sun Mar 06, 2016 2:39 am

Megatron wrote:x64 Version 0.8.34 build 5716

The second pass fails to utilize the GPU. I saw the GPU being utilized in the first pass but it was just cpu power in 2nd pass. I had slow preset and ticked use opencl if available. The rest was default AFAIK.

Am I using poor encoding choices or something?
I was just about to ask about this as well. No OpenCL in the second pass when using multipass crf.
my quant puzzles http://puzzles.nigelcoldwell.co.uk go look :)

flagpole
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Re: H.264, OpenCL & 2 pass

Post by flagpole » Sun Mar 06, 2016 2:45 am

saikat007saha wrote:Why is it not possible to use multi-pass crf in Mediacoder ?

I mean I want to use the first pass to determine the bitrate which will be
automatically used as the bitrate for 2nd encode.

When I tick multipass crf option in the 2 pass rate mode,
the process seems to be doing fine but the bitrate used for the 2nd encode is
always the same (irrespective of the crf value) and the one that is set in the bitrate value box.

I am attaching images below with red rectangles for the options I think
responsible for this behaviour.
so multipass crf: http://blog.mediacoderhq.com/two-useful ... 8-18-5333/
A check box labeled Multi-Pass CRF was added on the right of Rate Mode option droplist. By enabling it when 2-pass or 3-pass mode is chosen, video encoder (currently only x264) will do the first pass in CRF mode and a bitrate will be determined in result of the quality value specified. In 2nd pass or 3rd pass (if there is one), the encoder will still encode in the normal way but with the target bitrate set as is obtained in the first pass.

This feature is especially useful to users who like multi-pass encoding but still want the bitrate to be determined by the encoder (as if in CRF mode) according to the video content (resolution, frame rate, motion complexicty, image details etc.) to be encoded.
My understanding is that the distribution of the bitrate is determined by the CRF algorithm, and the absolute magnitude is determined by the bitrate set.

So you set the bitrate which will be detrmine the output size, or the average bitrate. Then you select multipass crf, which ignores the crf value. What else could it do.
my quant puzzles http://puzzles.nigelcoldwell.co.uk go look :)

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