[FFmpeg-user] Problem with vf pad ... help please

[Mark Himsley]

On 17/09/12 08:44, Christian Ebert wrote:
> * Mark Himsley on Monday, September 17, 2012 at 07:40:43 +0100

>> Yes - it is a common misconception.
>>
>> This BBC web page had lots of information, until the great web cull of
>> early 2011, so here's a link to the way-back-machine:
>>
>> http://replay.waybackmachine.org/20100826080627/www.bbc.co.uk/commissioning/tvbranding/picturesize.shtml
>>
>> This Adobe web page describes how they got it wrong all the way up
>> before After Effects CS4:
>>
>> http://help.adobe.com/en_US/AfterEffects/9.0/WS3878526689cb91655866c1103906c6dea-7f3aa.html
>>
>> This page also describes the difference between Adobe After Effects CS3
>> and CS4:
>>
>> http://www.mikeafford.com/blog/2009/03/pal-d1-dv-widescreen-square-pixel-settings-in-after-effects-cs4-vs-cs3/
>
> Thanks for the pointers - now I know why I had this nagging
> suspicion that something was not quite right DAR-wise with my
> transcodings. For the web I will probably crop so I can stay with
> "simple" aspect ratios, something like:
>
> -vf crop=iw-18:ih,yadif,scale=640:480,setsar=1:1

Does crop default to centred (I honestly cannot remember)? Otherwise 
you'll crop all 18 pixels off one edge.

And, if your video has sub-sampled chroma (422 or 420 for example) then 
you can only crop to even numbers, and you end up cropping 8 pixels off 
one side and 10 pixels off the other.

But, yes, that's the idea.

-- 
Mark