[FFmpeg-devel] [PATCH 2/3] avcodec/nvenc: Handle non-square pixel aspect ratios

[Kieran Kunhya]

On 17 January 2015 at 18:14, Nicolas George <george at nsup.org> wrote:
> Le septidi 27 nivôse, an CCXXIII, Philip Langdale a écrit :
>> On Fri, 16 Jan 2015 22:17:56 +0100
>> Nicolas George <george at nsup.org> wrote:
>> Ok. I did this test and it produces correct results - SAR 133:221 which
>> yields the correct final aspect ratio,
>
> This is a good start.
>
>>                                        but if I try and do a real world
>> case, like my PAL DVD, it goes wrong - and Timo's patch goes wrong too,
>> with this same weird 1.02 (45/44) scale factor.
>
> The 45/44 value looks like 704/720: the sign that some people long time ago
> in committees in the broadcast industry could not agree whether the aspect
> ratio applies to the whole image or only the part that is displayed on
> screen.

The active picture width is 702 pixels. I would read the following
thread and ETSI TS 101 154 for more information about SAR/DAR etc
https://lists.libav.org/pipermail/ffmpeg-user/2010-March/024551.html

I haven't quite followed what's going on to decide whether Nvidia or
FFmpeg is correct.

Kieran