16:9 picture with a 512x384 frame

[pooksahib]

Hi. I've a vid here that's been done as 4:3 when it should have been 16:9. I can resize it to 512x288 or I can click MeGUI's 'Clever Anamorphic' box and force 16:9. I'm thinking that the best option is to resize because, that way, every player will play it correctly whereas some players may not read the 'flag' in a 512x384 file. Is my thinking sound?

[hello_hello]

I always resize anamorphic video to square pixel dimensions when re-encoding these days, because a couple of players in our house don't pay any attention to MP4/MKV aspect ratios.

Mind you I'd possibly resize to something like 682x384 rather than reduce the height, given it's not exactly high definition. Or maybe compromise ands resize it to 640x360.

What sort of source file is it? You could try remuxing with MKVToolNix while setting a 16:9 aspect ratio and if your player displays it correctly you won't need to re-encode. Mind you I have a Bluray player that looks for aspect ratios in the video stream (at least for AVC) rather than a container aspect ratio, but you cpi;d change h264 aspect ratios with this version of ffmpeg, then remux with MKVToolNix wqhile setting a 16:9 aspect ratio so the stream and container aspect ratios are the same.
It's been a while since I've used it but my AnotherGUI preset for remuxing with that version of ffmpeg also includes the frame rate. I think it was causing some sort of problem when remuxing again with MKVToolNix if I didn't. You'd need to use sar=4:3 to make your source display as 16:9.

"C:\ffmpeg.exe" -i "C:\SomeVideo.mkv" -y -vcodec copy -acodec copy -vbsf h264_changesps=sar=4:3/fps=24000:1001 "C:\NewVideo.mkv"

If it's not h264 video, then none of that will help, but no doubt virtually every HD TV has a 16:9 mode, or a mode that'll stretch the video to fill the screen, and that should allow you to display any 16:9 video correctly as long as you don't mind switching to 16:9 mode if need be.

[jagabo]

I always keep the video anamorphic at the original frame size (only cutting away black borders) and only buy players that handle it correctly. And if the only problem is the AR, I would just remux and flag the AR at the container level.

[pooksahib]

Hi lads, and thanks. It's an xvid file and of no real importance so I don't mind what I do with it, really. But hello_hello's said something interesting: "I'd possibly resize to something like 682x384 rather than reduce the height". I just assumed that, when you resize, you couldn't/shouldn't increase either the width or the height. Does 'stretching' one or the other not cause any PQ deterioration, then?

[lordsmurf]

Re-encoding will decrease quality if you don't choose good settings.

Xvid/Divx was always a crap format, so it'll be hard to degrade it further. You may as well denoise the video while you're at it. I'd probably look to scale it 640x480, clean it up, and then output to 864x480 x264. Odds are it'll be better and smaller.

[hello_hello]

But hello_hello's said something interesting: "I'd possibly resize to something like 682x384 rather than reduce the height". I just assumed that, when you resize, you couldn't/shouldn't increase either the width or the height. Does 'stretching' one or the other not cause any PQ deterioration, then?

Reducing the height can potentially lose you some picture detail, because it lowers the resolution. Increasing the width doesn't lower the resolution, but it gives you more pixels to encode without adding any extra picture detail.

It's fairly common to stretch DVDs to something like 854x480 (16:9 NTSC) or 1024x576 (16:9 PAL) rather than reduce the height, although I live in PAL land and tend to compromise a little by resizing to 960x540 for 16:9. Or sometimes to 832x468 instead. It depends how much picture detail a DVD has and how much I can downscale without seeing a loss of detail..

When resizing DVDs by stretching the width, it can have a slight sharpening effect if you use a sharpish resizer, which I don't mind most of the time, even though technically it's altering the quality. The DVD video I used for these screenshots had already been sharpened, which is why by the fourth screenshot it's looking over-sharpened, but that's why I used it to demonstrate the effect of resizing the width.
https://forum.videohelp.com/threads/378501-Resolution-Bitrate-and-Quality#post2444902

I think for MeGUI, resizing "up" is disabled by default (for reasons I'll never understand). You need to go into the Avisynth Profile configuration via the AVS Script Creator and enable "upsizing" before MeGUI will resize the width "up".
Or try my CropResize script instead. I stopped applying cropping and resizing with MeGUI the day I finished the script and haven't looked back (I still use the script creator's preview though). It's so much easier, and no need to worry about aspect error.

To resize anamorphic video by only stretching the width, all you need to do is the following and the script will take care of the rest. You need to specify the correct input display aspect ratio for anamorphic sources.
CropResize(InDAR=16.0/9.0, ResizeWO=true)
If you want to apply cropping you can do it much like resizing and cropping with an Avisynth resizer. As an example, specifying a cropping of 12 pixels each side, 4 from the top and bottom, and telling the script to only resize the width.
CropResize(0, 0, 12, 4, -12, -4, InDAR=16.0/9.0, ResizeWO=true)

[jagabo]

I just assumed that, when you resize, you couldn't/shouldn't increase either the width or the height. Does 'stretching' one or the other not cause any PQ deterioration, then?

All resizing reduces quality. And all reencoding wtih lossy codecs reduces quality. The issue is what compromises you want to make. Upscaling the width or height requires more bitrate but you don't gain any real detail. Downscaling the width or height reduces the resolution and quality, and may require less bitrate. You also want to keep in mind how you plan to watch the video. In a little window? Then you probably don't need high resolution. Full screen on a big TV? Then you probably want to retain as much resolution as possible. And the sharpness of the source makes a difference. A blurry source can have the frame size reduced without losing detail.

[pooksahib]

Thanks again, guys. After careful consideration and a cup of coffee, I think I'm going to stick with the original framesize wherever possible. For DVD's, I'll crop the crud and then tick MeGUI's 'Clever Anamorphic' box.