Best settings for x265 encoding

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
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pmennen
Posts: 8
Joined: Sat Oct 10, 2015 11:56 am

Best settings for x265 encoding

Post by pmennen »

I typically convert video using older codecs (e.g. divx, mpeg4) to x265 and sometimes convert x264 to x265 when the bit rate seems excessive. I usually want outputs with relatively small file sizes (with bit rates in the neighborhood of 700-800 kbps for 720p resolutions) but of course I would like the best quality possible for those modest file sizes.

From what I understand, the software encoders should be used for best quality, but what about bit depth? I can choose between 8,10, and 12 bits. Is 12 bits better than 10 and is 10 better than 8? If so, what are the drawbacks of the 10 and 12 bit encoders. Is it just that it takes longer, or does the best choice depend on the source material?

Also is 2-Pass-Encoding superior to constant quality encoding? The predictable file sizes that you get from Avg Bitrate encoding is nice, but it seems that one needs two passes to get the same quality as the constant quality method. (But two passes usually feels annoyingly slow.)

I have an RTX2060 graphics card and the NVEnc encoder runs way faster than any of the software encoders. This is so much faster that it is pretty tempting to use even though from what I have read, the quality is not nearly as good for a given file size. Is the quality difference really that dramatic, and if so, why would they bother creating such a thing? Perhaps it would be better just to stick with x264 if encoding speed was so important.

Does the NVenc encoder only use 8 bit depth or is it possible to add switches in the Advanced Options field to use greater bit depths. Or are there any other switches that can be added to increase the NVenc quality (such as look-ahead, B-frames, etc).

Is Nvidea working on enhancing it's hardware x265 encoding so that we can use it in good conscience knowing that we haven't severely compromised the quality of our encodings for lack of patience in waiting for the slow software encoders to finish?

~Paul
mduell
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Joined: Sat Apr 21, 2007 8:54 pm

Re: Best settings for x265 encoding

Post by mduell »

Higher bit depth encoders are slow, so you have to user a faster preset to get the same performance. 12 bit is not widely supported.

Constant quality and 2 pass produce the same quality at the same bitrate, 2 pass just takes longer.

Hardware encoders like NVENC are for speed, typically targeting realtime or better even at high resolutions. To achieve that, they give up a lot on efficiency (quality for size). Each generation or two of cards from nVidia improves a bit, but still lags the software encoders.
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