Seeking to understand "vfilters" when transcoding

[SarasotaSlim]

I've been transcoding, using VLC for about a year, so I'm familiar with basic VLC
cmd-line syntax, etc, for using 'sfilter' and for changing audio and video codecs, etc.

But, I do NOT yet have familiarity with how to use VIDEO-filters, hence this posting.

Let's say I want to properly stretch a (movie) video, so that I purposely have some
black "letterbox" zones at top and bottom, and/or to end up with a specific aspect-ratio
(e.g. 16:9) for a movie that might NOT already be in that ratio.

Can someone either explain how to 'think' about this problem, or maybe better, just
illustrate with some cmd-line based snippets (that include some "vfilters") that
will accomplish that?

I've found some such example snippets here in the forum, but I haven't yet got
my head entirely around how to 'think', when it comes to choosing a "canvas"
size, etc, etc. (Maybe there's a VLC-specific tutorial somewhere that does
a decent job of explaining canvases and vfilters??)

Thanks in advance...

[Jean-Baptiste Kempf]

So, when you transcode, you should be using vfilter, like #transcode{vcodec=xxx,vfilter=grain} or so on. Some filter can't be transcoded, but this should be a bug.

[SarasotaSlim]

No...I guess my question wasn't clear or precise enough. I'll try again:

Ok, so what does stating a 'canvas' size accomplish?

e.g. in the docs/help info, it shows a snippet:

"transcode{vcodec=mp2v,vfilter=canvas{width=640,height=480}}"

[But, I already understand the syntax/layout rules. It's some better concepts and examples that I'm seeking.]

So, if one states a canvas size (different from the resolution of the input file's video-track), does
that then require one to also have a 'crop' or 'pad' clause, too?

Again, what I feel I need is a tutorial-like page or a few paragraphs, that mention a specific
goal, and then shows some sample snippets of a full vfilter that would accomplish that.

[mederi]

Using vfilter canvas tutorial
https://forum.videolan.org/viewtopic.ph ... 31#p381231

[SarasotaSlim]

Using vfilter canvas tutorial
https://forum.videolan.org/viewtopic.ph ... 31#p381231

There's some nice discussion and examples there. Thanks, Mederi !!