[FFmpeg-devel] [PATCH 2/8] decklink: Add support for output of Active Format Description (AFD)

Devin Heitmueller dheitmueller at ltnglobal.com
Fri Dec 29 23:02:41 EET 2017

> On Dec 29, 2017, at 3:48 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> 2017-12-29 19:12 GMT+01:00 Devin Heitmueller <dheitmueller at ltnglobal.com>:
>> +        /* FIXME: Should really rely on the coded_width but seems like that
>> +           is not accessible to libavdevice outputs */
>> +        if ((st->codecpar->width == 1280 && st->codecpar->height == 720) ||
>> +            (st->codecpar->width == 1920 && st->codecpar->height == 1080))
>> +            pkt->aspectRatio = ASPECT_16x9;
>> +        else
>> +            pkt->aspectRatio = ASPECT_4x3;
> I most likely won't use this (and I have never seen a decklink card)
> so please feel free to ignore:
> Similar code has caused some trouble with mxf files, is there
> really no saner solution? Like comparing what the actual aspect
> ratio is more similar to? Is SAR really always 1 for decklink?
> ("All the world's a VAX.")

So this is definitely a confusing block of code, and you aren’t the first one to ask about it (there were questions in the last round of review as well).  The aspect ratio referred to here is actually of the original coded video - not how it’s supposed to be displayed.  Hence, for example, 720x480 in widescreen with a non-square PAR would still have the aspect ratio set to 4x3, since that particular field describes the coded video (i.e. *not* how it’s supposed to be rendered).


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