[FFmpeg-devel] [PATCH] nvenc: Compensate for hardware trying to mess with aspect ratio of DVD content.

Philip Langdale philipl at overt.org
Thu Jan 22 05:29:25 CET 2015

On Thu, 22 Jan 2015 12:15:44 +0800
Agatha Hu <ahu at nvidia.com> wrote:

> We will fix the issue in driver, overscan compensation will be
> applied to input DAR *only* if the DAR is 4:3 or 16:9, otherwise
> won't unnecessarily modify the aspect ratio for resolutions like
> 720x480 and 720x576.
> The fix will be on future driver, I'll let you know when the branch
> is released.

Please, no. We do not want overscan compensation to be done by nvenc at
all. The compensation makes nvenc inconsistent with *all* other
encoders in ffmpeg. For every other encoder, if my input is 720x576 at
[64/45], then my output is the same. It does not do anyone any favours
for nvenc to implicitly alter the output DAR.

There is a separate discussion about whether DAR 'compensation' is
desirable in an encoder or not, but even if that discussion results in
a decision to apply DAR compensation at encode time, it will be done
globally in ffmpeg for all encoders - ie: at a layer above any
individual codec.

If nvidia feels it is important to offer this compensation 'feature',
then I would ask for a configuration option to turn it off - otherwise
we will need the 'de-compensation' logic in the patch I posted.



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