VideoHelp Forum

Try DVDFab and copy Ultra HD Blu-rays and DVDs! Or rip iTunes movies and music! Download free trial !
+ Reply to Thread
Results 1 to 8 of 8
Thread
  1. Hey there,

    so I'm currently trying to archive all my DVDs I got to stream them via Plex to my devices.
    I want to deinterlace the content and encode them with x264. However, things are pretty confusing for me when it comes to resizing and cropping.
    One DVD I have is a 4:3 PAL one with a resolution of 720x576. It has some borders around the picture so I need to crop it like that: Left:14/Right:14/Up:8/Down:8 and also want to convert it to square pixels in case one of my playback devices has issues with the aspect ratio etc. I am using StaxRip if that makes any difference.

    I have a few questions now:
    1. How do I resize the content the most efficient way? I have read this post https://bavc.org/blog/par-sar-and-dar-making-sense-standard-definition-sd-video-pixels but I still don't understand how exactly this works. Does that mean that the video I'm trying to encode has a true square pixel resolution of 720 wide OR 576 high? (Just to know if I should prioritize vertical OR horizontal resolution to not lose resolution) Let's ignore the cropping part for a bit, what resolution am I looking for?

    2. I am also confused about the DAR and PAR values. PAR 12/11 is MPEG4 standard and PAR 16/15 is for the MPEG2 standard. Since I am coming from a mpeg2 source, which one should I choose? Do I even need to set these values or do I just need to use a DAR of 1.333333 ? This way, without cropping - StaxRip is showing me a resolution of 720x544 with an aspect ratio error rate of -0,74%. Is this the full resolution I get when converting 576i to square pixels?

    3. Let's say the best res is 720x544 with a 1.333333 DAR and I crop the video using the above values. 692x528 is what comes to my mind but StaxRip won't let me do that - and to be honest, that's a very weird resolution. Is there any other res I should go for to not waste any pixels and avoid "upscaling" since I'll be cropping 28 pixels from the sides?


    I really hope someone is willing to help me with this as I am just so confused and don't know what to do. If you ask yourself why I want to resize and possibly lose detail is that I also want to deinterlace with QTGMC and crop the video so why not as well resize.


    Thank you in advance
    Quote Quote  
  2. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    The PAR of a 4:3 Pal DVD is indeed 16/15. The calculation is done on the horizontal. So


    720 /15 *16 = 768


    Thus you dvd displays as 768 * 576. And the maths to check that


    768 /4 * 3 = 576


    That resize to 720*544 should be avoided especially if you are cropping interlaced sources.
    Quote Quote  
  3. The PAR of a PAL 4:3 DVD is either 16:15=1.066667 ('generic') or 128:117=1.09402 ('ITU'). Unfortunately one does not know how the DVD disc has been authored by the studio, and it's nowwhere written on the disc. One can try to find out by doing the so called 'Circle Test' - if there is an exact circle seen straight from the front in the video. However, as the difference between the 2 variants is 2.5% only one has usually not worry much about picking the wrong one. Kind of nitpicking for most.
    An indication (but no proof) for 128:117 ('ITU') are small black borders left and right of about 8 pixels wide each. With no borders left and right one could assume a PAR of 16:15 ('generic').
    Quote Quote  
  4. Yes, the ITU spec for capturing analog video and the MPEG 2 spec differ as far as aspect ratios are concerned. Unfortunately, the difference is pretty much ignored by the industry.

    The generally accepted approximation of the PAL ITU spec is that the 4:3 image is in a 704x576 frame (the true value isn't 704, it's not even an integer, it's 702.something). So 4:3 = 704:/576 * 12:11. Most commonly a little extra is capture at the left and right in case the source or capture is off center, 720x576. So that full frame is a little wider than 4:3.

    The DVD spec indicates one should follow the MPEG 2 spec. The MPEG2 spec indicates the full frame contains the display aspect ratio. What's flagged in the MPEG2 data is only the display aspect ratio (for DVD only 4:3 and 16:9 are value). DVD's almost always use 720x576. So by the MPEG2 spec 4:3 = 720:576 * 16:15.

    When analog caps are made into DVDs (like all old BBC TV shows) the difference between the two specs is ignored. The 720x576 cap is written to DVD flagged as 4:3 DAR.

    The DVD players I've personally tested are schizophrenic about this. The upscaled HDMI output scales the full 720x576 to 1440x1080 then pads with black borders to 1920x1080. But the analog composite or s-video outputs handle the frame as the ITU specifies.

    DVDs made from analog caps are usually obvious. They're not very sharp (because the tape wasn't sharp) and there's obvious black borders at the left and right. I usually just crop them down to 704x576 and encode with 12:11 pixel aspect ratio. I occasionally see a 1:375:1 movie that's encoded with the MPEG 2 spec with small borders at the top and bottom.
    Quote Quote  
  5. Thanks for all the answers! This whole stuff is pretty confusing to people who have little to no experience with encoding.. especially when you have both PAL and NTSC DVDs (sometimes 4:3 ones with black borders on the top and bottom so a real aspect ratio of 16:9 - good thing is there aren't that many).

    @DB83 @jagabo
    The source file I have (remux of a DVD episode) shows up as video size: 768x576 in MPC-HC but in the MediaInfo tab it shows the actual video file is 720x576 with a 4:3 AR.
    In StaxRip it shows me that the source is also 720x576 with a PAR of 12:11 and a DAR of 1,367521.

    I only want to deinterlace the video, it doesn't really need cropping (maybe 2 left and 2 right but I'd rather not lose unnecessary details by resizing so I'm not gonna do that).
    I tried encoding it using StaxRips recommended values which match the values of the source (720x576 with a PAR of 12:11 and a DAR of 1,367521) - however when I play the file in MPC-HC using the Default DAR option it stretched a little bit to the sides (appearing wider) and setting it to 4:3 will make it look like the source file (when I play the source file, default dar and 4:3 look identical). So which aspect ratio is the correct one? It's hard to tell but I'd say the source file (4:3) looks more "real".

    When I change the DAR to 1,333333 (720x576) it looks the same as the source file when playing. However it gives me me a -6.25% AR error.
    As soon as I click the Resizing option, StaxRip changes the resolution to 720x544 (1,333333 DAR and -0,74% ar error) while only being able to resize down (704x528 for example would result in a 0,00% AR error). @DB83 you said 720x544 is not a good option, can I please know why?

    I can provide a sample if anyone is interested or you can add me on Discord PRiiXX#8800 if you're willing to help me.
    Quote Quote  
  6. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    I main reason, as I explained in my first reply, is to do with cropping. If you do not crop then that argument does not apply.


    But for future reference, if you cropped BEFORE you de-interlace and then resize there is a possibility that you create interlacing (jigglies) artefacts in your video.


    Now if you do the maths you will also note that 720*544 is not exactly 4:3. That would be 720*540. So why not resize to that ? That comes down to, what you may have read as, MOD or modulus where the numbers must divide by exactly 2,4,8 or 16 to guarantee playback on all devices and 540 fails that test.


    Of course if you go around the net you see 'dvd-rips' at 720*544. The majority of these are created with no knowledge of the underlying issues.
    Quote Quote  
  7. Originally Posted by sebastiaaan View Post
    I can provide a sample .....
    If the source is a PAL DVD with DAR (DisplayAspectRatio) of 4:3, no tool can tell for sure whether the PAR (PixelAspectRatio) of the active picture is 12:11 or 16:15.
    If the DVD source has been post-processed or re-muxed to a new format by some tool, the PAR may however be flagged somewhere (stream, container, or both - possibly even conflicting), but it still can be wrong, and depending on player capabilities or settings leading to different results (which is your experience, obviously).
    Eventually one has to inspect the source and try to find out what the PAR could be (best guess). A sample (few seconds) of the source video with hopefully a circle (wheel, logo, globe ....) in the picture would be helpful.

    Similar applies for an 4:3 NTSC DVD. The PAR may be 8:9 or 10:11 (practical approximation of 4320:4739)

    This link may be helpful:
    https://forum.doom9.org/showthread.php?p=1058927#post1058927

    As stated earlier: When the 4:3 PAL DVD 720x576 frame has small black borders left an right, one could assume in good faith that the PAR of the active picture is 12:11 (mpeg4, ITU approx.). When you crop left and right 8 pixels each side and encode the remaining 704x576 frame with 12:11 there should be almost no difference when you play it as forced 4:3 or according to the PAR.

    Edit:
    ... it doesn't really need cropping (maybe 2 left and 2 right...)
    Without seeing the picture this is an indication (but no proof) that the PAR is in fact 16:15 (mpeg2, 'generic').
    No proof, because if the Movie Aspect Ratio is 1.85 for example, the studio could have scaled it to 720x424 using the ITU (mpeg4) PAR of 12:11, and pad the top and bottom with black borders of 76 pixels height each, which give an overall frame size of 720x576 (including the top+bottom borders). In this case you would not see any left and right borders even though the PAR is 12:11. Of course, it would habe been more reasonable to author this movie for a DAR of 16:9 using a PAR of 64:45, means scaling it to 720x454 and adding top and bottom borders of 11 pixels height each.

    At the end you have to inspect the picture and make your best guess about the PAR. It is often not so obvious.

    Once you know the PAR you can always resize to square pixels if you prefer.
    Last edited by Sharc; 20th Oct 2020 at 12:17.
    Quote Quote  
  8. Originally Posted by sebastiaaan View Post
    The source file I have (remux of a DVD episode) shows up as video size: 768x576 in MPC-HC but in the MediaInfo tab it shows the actual video file is 720x576 with a 4:3 AR.
    That's because MPCHC is following the MPEG spec.

    Originally Posted by sebastiaaan View Post
    In StaxRip it shows me that the source is also 720x576 with a PAR of 12:11 and a DAR of 1,367521.
    That's because StaxRip is following the ITU spec.

    Originally Posted by sebastiaaan View Post
    I only want to deinterlace the video, it doesn't really need cropping (maybe 2 left and 2 right but I'd rather not lose unnecessary details by resizing so I'm not gonna do that).
    Then you have to decide for yourself whether the DVD is using the MPEG spec or the ITU spec and handle it appropriately.
    Quote Quote  



Similar Threads