[FFmpeg-user] loseless cropping from 1980x1088 to 1080 possible?

[gildororonar at mail-on.us]

Quoting "Zhang Weiwu" <zhangweiwu at realss.com>:
>
> Don't know what codec you used. If you use h.264

This indeed give me hints on how to refine my search, and it turns out
searching "crop h264" reveals a lot more information. I wasn't aware my
question is specific to h264 when I ask it, hence I never included "h264"
in my search key.

> There is a 'crop' field on the lower-right where you can type value  
> for t/b/l/r (top/bottom/left/right).

That seems to the equvilent of the following:

Quote from this article: Cropping h264 file without reencoding?
http://forum.doom9.org/archive/index.php/t-143990.html

> It is possible, by modifying the cropleft/croptop/cropright/cropbottom flags,
> but it won't save you any bits. Not like it costs any to begin with. And many
> decoders don't support cropping of >= 16 pixels, or cropping of top/left.

"it won't save you any bits" -> "video stream size remains" (I expected)

The same post talked about additional tools to do this.

The same post also reveealed you can do the cropping on the container  
level too:
Matroska container have cropping flags. I can see its use in removing  
letterboxes: you don't want to reduce quality by re-encode with -vf  
crop,
yet if letterbox to 16:9 movie is not removed, fullscreen play on an  
actual 16:9
screen would suffer from letterboxes both horizental & vertical. This
leaves people with only once choice: crop it in the container and accept
having additional bits that never gets displayed.

If you are right, that ffmpeg is not the right tool to crop h264 video stream,
would it be the right tool to set MKV crop flags?

Thanks for help!


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