LAV Filters - DirectShow Media Splitter and Decoders

tiresias · 18th October 2019, 18:29

Thanks for the clarification about the hardware decoder option.

I've been doing some more searching, and found some info specifically about the "DXVA2 native" and "DXVA2 copy-back" settings which I would like to clarify. Can I just run this by you for comments on what is right or wrong in the following statements:

If you are using the standard Windows EVR then it sounds like the best choice is probably "DXVA2 native" or "DXVA2 copy-back".

The setting "DXVA2 native" can only be used where the video decoder is connected directly to the renderer.

If there is a filter between the decoder and the renderer (or there is no renderer because we are outputting to a file) then "DXVA2 native" will drop back to software decoding.

If "DXVA2 copy-back" is selected, then you CAN use a filter between the decoder and the renderer and there is no drop back to software.

More recent GPUs are able to copy from video memory to system memory fast, so that there should not be a performance penalty in always selecting "DXVA2 copy-back" instead of "DXVA2 native" whether connecting directly to a renderer or not, or outputting to a file.

So, of the two settings, "DXVA2 copy-back" should always be selected, except that for OLDER GPUs that are slower to copy from video memory to system memory then selecting "DXVA2 native" may be more responsive when connected directly to a renderer.

Where "DXVA2 copy-back" is selected, regardless of whether the decoder is connected directly to the renderer or not, the decoder will use the first GPU that it finds to do the decoding, which might not be the same GPU that the renderer uses. In that case, is there a performance penalty or other problems where the decoder is using a different GPU to the renderer?

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18th October 2019, 18:29	#11 \| Link
tiresias Registered User Join Date: Apr 2004 Posts: 22	Thanks for the clarification about the hardware decoder option. I've been doing some more searching, and found some info specifically about the "DXVA2 native" and "DXVA2 copy-back" settings which I would like to clarify. Can I just run this by you for comments on what is right or wrong in the following statements: If you are using the standard Windows EVR then it sounds like the best choice is probably "DXVA2 native" or "DXVA2 copy-back". The setting "DXVA2 native" can only be used where the video decoder is connected directly to the renderer. If there is a filter between the decoder and the renderer (or there is no renderer because we are outputting to a file) then "DXVA2 native" will drop back to software decoding. If "DXVA2 copy-back" is selected, then you CAN use a filter between the decoder and the renderer and there is no drop back to software. More recent GPUs are able to copy from video memory to system memory fast, so that there should not be a performance penalty in always selecting "DXVA2 copy-back" instead of "DXVA2 native" whether connecting directly to a renderer or not, or outputting to a file. So, of the two settings, "DXVA2 copy-back" should always be selected, except that for OLDER GPUs that are slower to copy from video memory to system memory then selecting "DXVA2 native" may be more responsive when connected directly to a renderer. Where "DXVA2 copy-back" is selected, regardless of whether the decoder is connected directly to the renderer or not, the decoder will use the first GPU that it finds to do the decoding, which might not be the same GPU that the renderer uses. In that case, is there a performance penalty or other problems where the decoder is using a different GPU to the renderer?