Re-sizing DVD Mpeg2 files to get square pixels

[pippas]

If I de-interlace and re-size a PAL 720x576 16:9 DVD MPeg2 file so that it can be encoded to H.264 using square pixels, which way should I go :

1024 x 576 or 720 x 404 ?

I do appreciate that the second option is not quite the correct aspect ratio, and that I should always use the first option if I'm retaining the interlacing. In this case the output will be progressive....

The second option gives me smaller files, and I can't see any real difference in quality, but is the 1024 x 576 version really the 'correct' way to do it?....

[sanlyn]

It depends on the aspect ratio of the source image, not the DAR of 16x9. If the source is a movie, then likely its image aspect ratio isn't 16:9, as the only movies made as 16:9 are TV movies and TV programs. Maybe you could post an image of the video as displayed in a media player ?. Generally, though, 1024x576 should do the trick.

[pippas]

Thanks for your reply --- in this case, it is a movie made for TV, so a re-sized image at either 1024 x 576 or 720 x 404 both display with the correct aspect ratio.

I'm not intending the output for any disc authoring - I don't want to do the 'spinning disc' thing all over again - so I'm not confined to those specific ratios.

It was just really whrther there is any preference in upscaling the 720 to 1024, or reducing the 576 to 404.

Thanks for your information on the aspect ratio -- I can see alternative ratios may be needed for future projects, to get 'square' pixels to display the correct ratio.... there again, is it better to upscale one dimension, or downscale the other?.....

[sanlyn]

So for a simple resize:

to resize both horizontally and vertically, use 840x480. To resize horizontally only, use 1024x576. I'd go with the latter. Deinterlace (or de-telecine if it's progressive + pulldown) before resizing. Try Spline36Resize.

[NoBuddy]

to resize both horizontally and vertically, use 840x480.

I´m using in that case 854x480.
Don´t know, if there´s really a visible difference. It just makes me feel better.

[jagabo]

If I de-interlace and re-size a PAL 720x576 16:9 DVD MPeg2 file so that it can be encoded to H.264 using square pixels, which way should I go :

1024 x 576 or 720 x 404 ?

Either way you want. Or any other ~16:9 frame size. 1024x576 retains more vertical resolution but will require a higher bitrate. 720x404 looses a little vertical resolution but won't require as much bitrate.

[pippas]

Thanks ---looks like I might have another look at 720 x 404.. Smaller file size with no apparent loss of visual quality - (at least there isn't on a 22" monitor!).......

[sanlyn]

720x404 will work, but it's a tad wider (1.782:1) than 852x480 (which is closer to 16x9 at 1.772:1), but either would do. I've seen 852x480 recommended for square-pixel standard def PAL by apps like Premiere Pro -- and some other high-end apps will come up with all kinds of minor variations. Likely it doesn't make a great deal of difference. They're both mighty close. The simple formula is (vertical size * 1.777777778), and the resulting numbers should be multiples of 4 or rounded to make it that way. You can't multiply many numbers by 1.777777778 and get something that doesn't have decimals anyway.

I'd like to have a discussion with the people who designed these standards.

[jagabo]

Nobody can see a 1 or 2 percent aspect ratio error. Don't worry about it. In the days of analog CRT TVs most TVs were off by more than that and nobody cared.

[Cornucopia]

@Sanlyn, I think you might be mistaken on that. The ~852x480 rez bandied about has by my recollection ALWAYS been in reference to NTSC footage, not PAL.

@OP,
Throughout these kinds of processes, I'd say a guiding principal should be, "do the least harm."

The first thing I would do with this footage is check to see whether the intended target players support non-square pixels. If they do, LEAVE IT that way. Whether you re-encode or not (with it's accompanying loss of quality), you avoid ADDITIONAL loss of quality via the resize.

If you have to have Non-square pixels, then resizing in only one dimension (the horizontal) would be the lesser of the evils. # of Lines is tied in a 1:1 correspondence between analog and digital images; it's the horizontal pixels that get fudged with their pixel AR and # to accommodate the A->D digitizing transformation. Same reason you need to maintain interlace integrity (whether de-interlacing or not).

In that case, it makes more sense to me for you to resize to 1024x576. Filesize & bitrate consideration should enter into it, but aren't the dictators they used to be since technology has advanced so much.

Only reason I see NOT going that route would be if your player(s) was SD-resolution-bound and was wired to not accept anything over 720x576 (many legacy chip-based units have been).

Scott

[pippas]

Thanks for your advice and guidance. I have had problems in the past with some containers (MKV and AVI for example) apparently ignoring AR flags, with some players. As the current project files may be played on a variety of players, I think I'll take the quality hit and go for square pixels, in this case.

But do understand your 'less is better' comment...... Thanks again for your advice

[sanlyn]

AVI itself has no DAR playback flags, they just play as-is. So 720x576 that will be encoded as 4:3 or 16:9 will just play back in AVI format as 720x576. With some media players you can specify the AR you want.

[Cornucopia]

@Sanlyn, the AVI container format doesn't have EXPLICIT AR flags per se, at the container level (though good implementations have always used a comination of calculations of container resolutions vs. display resolutions), but many if not MOST of the AR uses with AVI is done not at the container level, but within the video stream info. There, many video codecs make use of AR: DV, MPEG2, Xvid/Divx/Mp4v2, AVC/h.264, etc. Any DECENT player should be looking to those anyway.

@OP, MKV does have explicit AR flags, so a player that doesn't support that is just "non-compliant". But since MKV doesn't really have a compliance-enforcement entity, it's no surprise you see a wide range of playback capabilities using the MKV format.

Good luck,
Scott

[sanlyn]

Yes, I realize that some AVI containers have those flags, depending on the compressor/encoding.