Question about resolution of xvid videos

[M4ST3R]

Many xvid rips have a resolution of 624x352. I guess it's not the original resolution. Then why is it resized? Is it because for the same bitrate (let say 1000 kbits) 624x352 has a better visual quality than 720x576, because there's less pixels to encode? Or for another reason?

[n0an]

Yes, at lower bitrates than the source, you need to resize the frames to provide sufficient bits to each pixel. This is also affected by the duration of the video clip - you would want to keep lower resolution for say a 2hr compared to a 1hr movie.

When you say "720x576", I assume you are referring to a PAL DVD, not a downscaled blu-ray. A NTSC DVD is 720x480.

[M4ST3R]

Yes, I'm going to backup some PAL DVDs. I will probably encode them at about 2000 kbits and I'm wondering if I should keep the original resolution or resize to 624x352 or another resolution.
Most guides I read speak about resizing/cropping when you remove black bars but don't suggest to reduce the resolution to increase the visual quality. But since I see a lot of rips done at 624x352 I was wondering the reason why.

[7ekno]

Many xvid rips have a resolution of 624x352. I guess it's not the original resolution. Then why is it resized?

Nothing to do with bitrate, more to do with "Display Ratios", "Storage Ratios" and "Pixel Aspect Ratios" ... the AVI container does contain a flag to set a "Pixel Aspect Ratio", however nearly none standalone DivX players, and very few PC media players actually pay ANY attention to the flag ...

So if you dump a DVD into AVI (irrespective of codec used), it will likely be displayed at 720x576 resolution (which is a "Display Ratio" of 1.25 ... ever heard of a 5:4 TV set?!? Most are 4:3, 16:9 or 2.35) ... so putting 720 x 576 into an AVI file will make everything look "squished" ...

Options are:
- use MKV with 720x576 res and an appropriate Aspect Ratio flag (all MKV players enforce the Aspect Ratio)
- use 704 x 384 (or whatever resolution mimicks the given aspect ratio in square pixel), significantly reducing vertical resolution and subsequently losing alot of detail
- use 1024 x 576 (or whatever the Aspect Ratio dictates) which keeps all vertical detail, but wastes encoding bits due to the interpolated 1024 width.
- use AVI with 720x576 wth appropriate aspect ratio flag and pray that whatever you are playing it back on actually uses the aspect ratio flag ...

7ek

[M4ST3R]

You're right. I'm dumb, for some reasons I thought that 720/576=624/352=1.25

Thanks!

[n0an]

7ekno: I suggested resizing to a lower AR for lower bitrates.

[7ekno]

I guess the point being, if you want to retain the most detail without wasting bitrate while having predictable results on a wide range on playback devices, your only option is the MKV container with DAR specifically set from source keeping the full 720x576 resolution ... and of course the best encoder would be x264 :)

Tek

[rtjnyoface]

But since I see a lot of rips done at 624x352 I was wondering the reason why.

I can only assume it is in hopes of gaining quality. Smaller resolution=less bits needed.

For your situation I would still crop the black bars but keep the resulting resolution (as you will gain quality). Either way, @ 2000 kbits its going to look pretty darn good for most people.