[FFmpeg-user] How do I increase the playback size of a video without rescaling it?

Moritz Barsnick barsnick at gmx.net
Fri Jul 17 00:20:30 EEST 2020

On Thu, Jul 16, 2020 at 12:39:03 -0500, fowman wrote:
> Just this, but then it's the only one I have :-)

It can't be that difficult to find other 1280x720 recodings, can it? Or
to create your own?

> Here is ffprobe info:
> Original .ts file recorded by my Humax:
> Stream #0:0[0x931]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002),
> yuv420p(tv), 704x576 [SAR 16:11 DAR 16:9], max. 15000 kb/s, 25 fps, 25 tbr,
> 90k tbn, 50 tbc
> 1280x720 .mp4 exported from OpenShot:
> Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720,
> 14925 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)

That doesn't tell me whether the content includes boxes. Unless you run
it through the cropdetect filter.

> I realise that the original .ts video is actually letterboxed, although the
> vertical side bars are pretty narrow. I've always assumed that letterboxing
> referred to the top and bottom horizontal bars and was just a side effect of
> playing a widescreen movie in a 16:9 or 4:3 display.

I'm not referring to a side effect. I meant true black "boxes" or
borders, included in the encoded frames.

What often used to happen was that (true) 16:9 content was amended with
bars to make it 4:3. If you then play that (4:3 enconding) fullscreen
on a 16:9 screen, you will have the explicit top/bottom bars, and newly
introduced left/right bars, to fill the encoded 4:3 back up to 16:9,
instead of snipping something away, obviously. In total, this would
give you a big box around your content, despite full screen.

In your case, there might be a big box there (which we could see if we
saw the actual viedo), or said "clean-aperture" (CLAP) marking, which
could have funny effects. Come to think of it, those effects should be
opposite, i.e. the clean aperture should enforce cropping of
non-displayable segments.


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