gop-ref-dist and gop-pic-size

gop-ref-dist and gop-pic-size

SDK seems to use gop-ref-dist 3 by default. Are higher values recommended like 4 and 8? I found one video with a colour distortion when using gop-ref-dist 4. Not sure if this is a bug. It puzzles me that some videos look better with different gop-ref-dist numbers. Very different behavior.

What gop-pic-size is used by default from the SDK? I can't find a number and it's almost impossible to reproduce the number used by the SDK.

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For more complete information about compiler optimizations, see our Optimization Notice.

The default GOP pattern values chosen by the Media SDK implementation are generally chosen to produces the desired "Target Usage".  If the requested target usage if for best speed, the values may be different than if usage is for best quality.  The numbers chosen are Intel's recommended values for the implementation (hardware/drivers) for the usage models Intel has anticipated.  We are consistently seeing new usage models and we are always interested in hearing about the experience of your users.  If you have content and/or usage model the appears to be better with other values, please let us know as it helps us plan for (even better) products in the future.

If you see unexpected distortion, one way to anaylize if it is a bug in the implementation is to compare encoded outputs of the software library (libmfxsw.dll and init with "MFX_IMPL_SOFTWARE") and with the results when using Intel Quick Sync Video (hardware).

THANKS

-Tony

Default SDK gopsize is 256 (TU4) which I figured out after some testing. I haven't tested if it differs with other TUs. Yes I saw much better results with other gopsize values. The main problem is that it depends on the input video. I will post some examples later.

I have a couple of examples for you. First if all the Avatar issue I'm seeing. Everything tested with VBR+mbbrc bitrate mode of about 5000 kbps output bitrate in 1080p.

Avatar Original screenshot: http://img22.imageshack.us/img22/5971/xn1j.png
gop-ref-dist=default:gop-pic-size=289: http://img132.imageshack.us/img132/8343/sk.png
gop-ref-dist=default:gop-pic-size=default= http://img12.imageshack.us/img12/6402/vxe.png

The colours look perfectly fine with goppicsize=289 whereas with Intels default they look slightly wrong compared with the original screenshot. Can you see this? Here some more examples how different gop values can increase the quality over Intels default.

gop-ref-dist=default:gop-pic-size=default= http://img43.imageshack.us/img43/6702/dltg.png
gop-ref-dist=8:gop-pic-size=default= http://img38.imageshack.us/img38/4236/26fh.png

gop-ref-dist=default:gop-pic-size=default= http://img11.imageshack.us/img11/6706/2ios.png
gop-ref-dist=8:gop-pic-size=default= http://img208.imageshack.us/img208/4092/y86.png

gop-ref-dist=default:gop-pic-size=default= http://img607.imageshack.us/img607/9900/uukz.png
gop-ref-dist=8:gop-pic-size=285= http://img809.imageshack.us/img809/3188/ndpi.png

The gop behavior of Intel Quicksync is often suboptimal. This is the biggest problem. With suitable gop values for the video the quality can reach some better x264 presets.

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