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

[Kieran Kunhya]

On 17 January 2015 at 23:38, Nicolas George <george at nsup.org> wrote:
> L'octidi 28 nivôse, an CCXXIII, Kieran Kunhya a écrit :
>> The behaviour of the Nvidia code I believe is correct.
>> As far as I understand it corrects SAR for 720-width content to comply
>> with BT601.
>
> That is just not true.
>
> Basic principle: THE COMPETENT USER IS RIGHT.
>
> If someone knows BT601, and knowing it decide to produce a video that does
> not conform to it, for example writing "testsrc=s=720x576,setsar=64/45",
> then the software must comply.

No, the user who doesn't want BT601 should override it.

You don't realise this but there are many orders of magnitude more
BT601 content than any other content with a 720x480 or 720x576
resolution. This is what the vast majority of users are processing
with FFmpeg.

> There is a very simple way of flagging content that is supposed to comply
> with BT601: the SAR is 512/351. If SAR is 64/45, that means someone before
> nvenc decided that the video is not expected to conform with BT601, and
> nvenc has no right to decide otherwise.

You fail to realise this but SARs are not necessarily arithmetic for
historical reasons.

Kieran