[MPlayer-users] Transcoding from one aspect ratio to another

[JD]

On 11/03/2010 10:00 AM, Stephen Mollett wrote:
> Hi,
>
> On Wed, 3 November, 2010 16:06:56, JD<jd1008 at gmail.com>  wrote:
>> I have a video file that has an aspect ratio of 2.353 : 1
>> I would like to  transcode it to an aspect ratio of 1.6 : 1 (like 1280x800).
>> Is this even  possible?
> You have two choices - either add black bars top and bottom ("letterboxing")
> using "-vf expand=..." (see the man page or documentation) or crop the left and
> right off with "-vf crop=...". You could also do a bit of both so that you lose
> a little less at the sides and have smaller black bars. Either way, you will
> also need to scale the video appropriately in one or both dimensions using -vf
> scale. I'd probably crop first (so the scaler has less work to do), then scale
> and finally expand (scaling after expanding is generally a bad idea as it will
> blur the edges of the black bars and waste bits).
>
> If the video is already letterboxed (a DVD will most likely be encoded as
> 16:9/1.78:1 with black bars to make it 2.35:1), you might want to first crop off
> the existing black bars so that you're just working with the active part of the
> picture. "-vf cropdetect" might help you here.
>
> If you're a bit of a perfectionist (like me), you might want to consider the
> characteristics of the video codec when setting the size of the black bars in
> the final video stream - most codecs work best when the width of the bars (and,
> of course, of the video between them) is a multiple of 16 pixels so you may need
> to trim a few pixels from the picture to get it exactly right even if you're
> only letterboxing it.
>
> Hope this helps,
> Stephen
>
Very good points Stephen.
I will try to implement as best as I can.

Cheers,

JD