Finding the correct AR

[shroom]

Hi,

I'm rather new to the encoding world, though I've already gathered some nice infos on avisynth.
But there's something I've never really taken care of (I usually let MeGUI deals with it) : the aspect ratio.

I have various old videos I'd like to re-encode in today's standards and after doing basic before/after checks, I notice some differences.
Most of the time, people are slightly "compressed". Something you can't really notice unless you compare both original and result.

Here's one example :

MPC-HC says :
- 352 x 240 (AR 13:10)
- MPEG1 Video 352x240 (107:80) 29.97fps

So I know you can set the AR no matter what the resolution is, but here I have 3 different values within the same software :
- 352x240 = 1,4667
- 13:10 = 1,3
- 107:80 = 1,3375

Then if I check with MediaInfo, I get :
- Display aspect ratio : 4:3 (which is 1,3334)

Last but not least, MeGUI loads the video and set the DAR to ITU 4:3 PAL (1.367521) / NTSC.
And the video previewed is already slightly compressed, before doing any modifications.

So which one is the good AR ?
Does my eyes trick me (as the vid rendered in MPC-HC really seems the good one) ?

[TheSkiller]

Assuming your video is in fact quarter NTSC (is it a VCD?) the Pixel Aspect Ratio is the same as for full NTSC, 10/11. Actually, with a width of 352 or 704 you can omit the calculation because it is clear that with ITU compliant NTSC video of these widths the aspect ratio of the picture (DAR) is always simply either exactly 4:3 or 16:9, this does not apply to other widths like 720, 480 and 544.

Nevertheless, this is the simple calculation using the simplified NTSC PAR of 10/11:

352 * (10 / 11) = 320 (mathematically the brackets are not needed)

Height stays the same (240). You're left with 320x240 square pixels which is exactly 4:3 (1.333). This means you can upscale your 352x240 video to whatever exact 4:3 resolution you want.


I don't know where these weird numbers come from (like 13/10), those don't make sense.

[shroom]

Yes, most of them are VCDs.

Adjusting to 4:3 in the avisynth script did the job, thank you for your explanation :)

[MrVideo]

Why would one want to throw away more horizontal resolution by converting the non-square pixel 352x240 to 320x240?

Also, you really don't gain anything by taking the MPEG-1 VCD video and converting them to H.264. All you are doing is adding another recode step that does reduce the quality a little bit, because each digital recode, is a lossy recode.

[shroom]

Also, you really don't gain anything by taking the MPEG-1 VCD video and converting them to H.264. All you are doing is adding another recode step that does reduce the quality a little bit, because each digital recode, is a lossy recode.
Yes, I know that.
But it's not just a re-encode as I'm trying to fix the colors and some of the artifacts of those old VCDs.
I wouldn't spend time converting them otherwise.

[Ghitulescu]

Most of movies sold on VHS/VCD/LD are now remastered and reissued on DVDs. IMHO it's not worth spending time, energy, work when one can spend 1-10€ (depending on many factors ;)) - unless, of course, the DVD versions suffer from reediting (sometimes the VHS version is slightly different than the newly DVD one).