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  1. Member 2Bdecided's Avatar
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    Originally Posted by jagabo View Post
    I've never seen a commercial 16:9 DVD with a 704x576 (or 704x480) frame size.
    My neither. But then I've never seen a commercial 4x3 DVD with 704x576. I believe they exist, but they're the minority. Simply, most professional workflows (encoding and authoring) are set up for 720x576.

    I was telling him the proper way if he wants a 720x576 frame.
    I have plenty of 720x576 4x3 DVDs, and in every case the 4x3 video sits in the middle 702x575 pixels - exactly the opposite from what you're telling him to do. So I'd be very cautious about describing scaling 4x3 to fill 720x576 as the proper way.

    Cheers,
    David.
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    Thanks for your concern, but there's no need, at least not on my part. I digested all that was said here and that I could find elsewhere, tried out in practice all the options (with DB83's help ) and came to the conclusion that there's still no one-size-fits all solution, because on the computer even a 704-pixel encode does not display correctly
    Originally Posted by fvisagie View Post
    Even if this comes out symmetrically on a digital output, there are still some caveats. This comes out too narrow on PC (because we started off with a Rec.601 DAR 1.366 picture now displayed at 1.333), and there's loss of horizontal resolution as jagabo points out above.
    Taking that into account, along with the fact that there's still further loss of horizontal resolution through blanking on my TV at least, and the fact that at worst the error of a standard 720-pixel encode is ~2.5% on whatever equipment, I took the monumental step - for me - of accepting the status quo as a compromise!
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  3. Originally Posted by 2Bdecided View Post
    So I'd be very cautious about describing scaling 4x3 to fill 720x576 as the proper way.
    I quoted and linked to the MPEG 2 specification. I told him that the behavior of DVD players can go either way. And I told him that the issue is usually ignored on commercial DVDs made from analog tape. I even suggested he ignore the difference himself.
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  4. Member 2Bdecided's Avatar
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    Originally Posted by jagabo View Post
    MediaInfo is assuming the full frame holds the 4:3 DAR. I haven't seen the DV spec myself, but as I understand it, DV uses rec.601 scaling. So MediaInfo appears to be incorrect for both PAL and NTSC 4:3 DV. But I wouldn't take that as the final word until someone can quote the DV spec.
    There's a screen capture of the relevant page of the spec over on Doom9 (in the DV forum IIRC). It confirms 13.5MHz Rec601 sampling.
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  5. Member 2Bdecided's Avatar
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    Originally Posted by fvisagie View Post
    720x576 PAR 59:54 -> 704x576 PAR 12:11 I guess, i.e.
    Code:
    Spline64Resize(704, 576)
    from the 720x576 input?

    That makes sense if you reason as follows: the "4:3" Rec.601 720x576 source holds a symmetrical picture in 720 horizontal pixels (if displayed at 1.366 granted), the analogue DVD->TV conversion presents the picture in ~704 pixels, and for that to be symmetrical, the full Rec.601 width of 720 must be resized to 704. That's how it works here at least, see attached.
    Are you sure it's not cropped? It is here, sometimes with nice gentle windowing, sometimes with a hard single-pixel transition. I have several DVD players, pixel-accurate test discs, underscan monitors, and a couple of decent scopes. I only have a couple of DVD players with HDMI outputs, and I've not tested a BluRay player.

    Even if this comes out symmetrically on a digital output, there are still some caveats. This comes out too narrow on PC (because we started off with a Rec.601 DAR 1.366 picture now displayed at 1.333), and there's loss of horizontal resolution as jagabo points out above.

    edit: It's clear that the analogue DVD->TV conversion still stretches, then blanks the 704-wide picture. If it displayed all horizontal pixels as encoded, the picture would have come out as on the computer, i.e. ~2.5% too narrow. Therefore, there's double loss of horizontal resolution: resizing from 720 to 704, and then the analogue conversion throwing away another ~8+8 pixels. 32 in total from 720, hm...
    There is zero resolution loss anywhere if you use 704. You crop to 704 (no scaling). The player outputs 704 (no scaling).

    You also get the same shaped output on analogue and (at least some) digital outputs.
    You also get a proper 4x3 display on the PC.

    The only potential worry is that if your camcorder captured some nice usable pixels outside of the 4x3 aperture (i.e. outside of the centre 704 pixels), you'll have to throw them away to get 704 (they were never meant to be seen anyway). Deshaker is going to throw _far_ more away. The alternative is to accept some kind of aspect ratio error.

    Cheers,
    David.
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    Originally Posted by 2Bdecided View Post
    There is zero resolution loss anywhere if you use 704. You crop to 704 (no scaling). The player outputs 704 (no scaling).

    You also get the same shaped output on analogue and (at least some) digital outputs.
    You also get a proper 4x3 display on the PC.
    I now redid all 3 tests and burnt them all to the same DVD: untouched (just inputing via OpenDMLSource to use the Cedocida codec with YV12 MPEG-2 interlaced chroma sample placement and frameserving to ffmpeg), cropped to 704 (Crop(8, 0, -8, 0)) and scaled to 704 (Spline64Resize(704, 576)).

    The results are
    Code:
                   PC error         Analogue TV error
                   --------         -----------------
    untouched      2.4% too tall    1.5% too wide
    cropped 704    0%               1.5% too wide
    scaled 704     2.4% too tall    0%
    
    %error calculated wrt. vertical size
    The PC results fit my expectations. The first and last of those show that the same picture information is retained and displayed within a 4:3 display area in both cases (albeit at lower encoded resolution in the latter).

    The TV results don't fit in with my expectations (and with what I think you're saying) at all. The first two of those seem to indicate/confirm that the DVD/TV combination only uses the centre 702~704 pixels. However, all of them, but especially the last where the horizontal scale was compressed before encoding, seem to indicate that my DVD/TV combination stretches too much horizontally? Can I kindly ask you and jagabo to confirm how these come out on your equipment?

    At this point, these results would then suggest I should take my DVD/TV's rendering with a bag of salt, take into account that theory suggests a 704 cropped should display near-correctly on most equipment, realise that also with my DVD/TV the 704 cropped error at 1.5% is no worse than with any other input format on that equipment, and make the decision to crop to 704 and encode?
    Image Attached Files
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  7. Member DB83's Avatar
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    But did you not say that my 704*576 sample appeared 'perfect' on your tv.

    The difference is that there was no cropping as such. Surely a crop just retains whatever PAR existed which then carries forward to the re-size that you did.

    Try, just try, my method which simply encodes your DV in mpeg2 at 704*576 - no cropping - and create a dvd from that.

    Not sure if our American friends can help here since 704*576 is part of the PAL dvd standard and not the NTSC one unless they have a player/tv that fully supports PAL
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    Originally Posted by DB83 View Post
    But did you not say that my 704*576 sample appeared 'perfect' on your tv.
    ...
    Try, just try, my method which simply encodes your DV in mpeg2 at 704*576 - no cropping - and create a dvd from that.
    This is how that sample you refer to displayed here:
    Originally Posted by fvisagie View Post
    this displays ~2.5% too tall on my monitor as expected, but perfectly on my composite DVD output.
    which - of the 3 tests in the last sample I did above - corresponds exactly with this particular one
    Originally Posted by fvisagie View Post
    ...scaled to 704 (Spline64Resize(704, 576)...
    Code:
                   PC error         Analogue TV error
                   --------         -----------------
    untouched      2.4% too tall    1.5% too wide
    cropped 704    0%               1.5% too wide
    scaled 704     2.4% too tall    0%
    
    %error calculated wrt. vertical size
    You took 720x576 source and encoded it to 704x576 (which actually first scales to 704x576 in the encoder before encoding), whereas I prescaled to 704x576 in Avisynth and then encoded as is. Same output format, same result.

    edit: BTW, how does my cropped 704 above come out your side (assuming you have analogue equipment to display it on)?
    Last edited by fvisagie; 18th Mar 2013 at 06:32.
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  9. Originally Posted by fvisagie View Post
    The results are
    Code:
                   PC error         Analogue TV error
                   --------         -----------------
    untouched      2.4% too tall    1.5% too wide
    cropped 704    0%               1.5% too wide
    scaled 704     2.4% too tall    0%
    
    %error calculated wrt. vertical size
    What are you measuring in those videos? I don't see any obvious squares or circles.
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  10. Member DB83's Avatar
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    Ok. I misread your remarks about 'cropping'. I do not think I can help you with the practicalities as I only have a 16:9 HDTV with upscaling from the dvd-player.
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    Originally Posted by jagabo View Post
    What are you measuring in those videos? I don't see any obvious squares or circles.
    There's a circle drawn on the paper that starts at the top, and fills it left-to-right. Sorry it's so faint, but it's just usable.

    Originally Posted by jagabo View Post
    No, to convert rec.601 to MPEG you crop the picture to 702x576 then scale to 720x576
    Disregarding any debate on 702 vs. 704 I suspect now where scaling back to 720 might make sense in theory at least. If one starts off with Rec.601 PARs, your centre ~704 should end up in the 4:3 display. So you might as well crop to 704 and work on that throughout, which is what I think David is suggesting.

    From those 704 horizontal pixels the DVD player will construct a horizontal scanline. I.e. it will effectively 'scale' the 704 pixel samples to the required length of a standard scanline. If you scaled the 704 to 720 beforehand using a high-quality resizer in software and still encode to a 4:3 aspect ratio, the player will have the benefit of greater sample resolution when constructing the scanline (i.e. the required scaling factor will decrease), while hopefully the high-quality software resizer will give better results than whatever algorithm the player uses.

    In your experience, does this make any significant difference either way? I'll obviously have to also test it.
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  12. Originally Posted by fvisagie View Post
    Originally Posted by jagabo View Post
    What are you measuring in those videos? I don't see any obvious squares or circles.
    There's a circle drawn on the paper that starts at the top, and fills it left-to-right. Sorry it's so faint, but it's just usable.
    Ah, I see it now. But it goes off the bottom of the frame.

    Originally Posted by fvisagie View Post
    Originally Posted by jagabo View Post
    No, to convert rec.601 to MPEG you crop the picture to 702x576 then scale to 720x576
    Disregarding any debate on 702 vs. 704 I suspect now where scaling back to 720 might make sense in theory at least. If one starts off with Rec.601 PARs, your centre ~704 should end up in the 4:3 display. So you might as well crop to 704 and work on that throughout, which is what I think David is suggesting.
    Yes.
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    Originally Posted by jagabo View Post
    But it goes off the bottom of the frame.
    I can only think that your player somehow crops top and bottom, there's quite a bit of margin. How does that compare to what you see on the computer?

    Yes.
    And the rest, about scaling back to 720 to reduce amount of scaling required during playback?
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  14. Originally Posted by fvisagie View Post
    Originally Posted by jagabo View Post
    But it goes off the bottom of the frame.
    I can only think that your player somehow crops top and bottom, there's quite a bit of margin. How does that compare to what you see on the computer?
    LOL. My mistake. I quickly opened the files with VirtualDub (which displays the video pixel-for-pixel) and saw the circles going off the bottom of the window. But I had just worked with NTSC material so the window was ~720x480, not 720x576!

    If you want to work with some clearer test patterns:

    Click image for larger version

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    Click image for larger version

Name:	704x576.4x3 DAR padded to 720x576.png
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    Click image for larger version

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    With devices that follow rec.601 PAR scaling the white box should be square in the first two images (704 and 704 padded). With devices that follow MPEG 2 scaling the box should be square in the last image (720).

    The 704-padded-to-720 image has the edge markers moved out rather than just padding with black borders. That way you can tell if the player crops the edges of the frame or includes it.
    Image Attached Files
    Last edited by jagabo; 18th Mar 2013 at 09:10.
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    Originally Posted by jagabo View Post
    If you want to work with some clearer test patterns:
    Very handy thanks.

    Do you perhaps have patterns with vertical lines of gradually decreasing thickness, with which to compare horizontal quality on the player of 704x576 vs. 704x576 scaled to 720x576 encodes?
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  16. Originally Posted by fvisagie View Post
    Do you perhaps have patterns with vertical lines of gradually decreasing thickness, with which to compare horizontal quality on the player of 704x576 vs. 704x576 scaled to 720x576 encodes?
    Yes, I have such patterns. Most are set up for NTSC but you can pad the top and bottom of the frame to make PAL versions.

    Click image for larger version

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ID:	16826

    Click image for larger version

Name:	Resolution slanted lines 720.png
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ID:	16827

    But it's very hard to compare this type of pattern because of moire problems.
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    Originally Posted by jagabo View Post
    With devices that follow rec.601 PAR scaling the white box should be square in the first two images (704 and 704 padded). With devices that follow MPEG 2 scaling the box should be square in the last image (720).
    THAT was a useful edit! Thanks, also for the other patterns.

    With the 7nnx576 patterns my DVD/TV come out as follows:
    Code:
                                        Analogue TV error
                                        -----------------
    704x576.4x3 DAR                     2.2% too wide
    704x576.4x3 DAR padded to 720x576   2.2% too wide
    720x576.4x3 DAR                     5% too wide
    
    %error calculated wrt. vertical dimension
    For completeness I redid the previous actual camera footage tests with clearer images this time, attached. The results follow the previous ones:
    Code:
                   PC error         Analogue TV error
                   --------         -----------------
    untouched      2.4% too tall    2.6% too wide
    cropped 704    0%               2.6% too wide
    scaled 704     2.4% too tall    0.4% too wide
    
    %error calculated wrt. vertical dimension
    So it's becoming fairly inescapable that my TV display is out of spec? In other words, I can't use that equipment as guideline (I'm authoring for other people) and I should instead just aim for picture content of 704 pixels with this Rec.601 camera. For certainty though I'd be very grateful if you could compare inputs and results, please?

    So what do you think of the idea of aiming for less DVD scaling and better output by pre-scaling the 704 picture content to 720 pixels before encoding?
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  18. I had a chance to make a PAL DVD from the earlier AR test patterns. I made three 4:3 DAR m2v encodings, one from each image (no scaling of the images before encoding). I made a fourth m2v using ReStream to add a sequence display extension to the 704-padded-to-720 m2v, indicating the 4:3 DAR was in a 704x576 sub frame. From the top down on the DVD menu:

    1) 704x576 4x3 DAR padded to 720x576: This uses rec.601 PAR (assuming 704x576, not ~702x576) with the frame padded to 720x576. When following the rec.601 spec the full frame should appear slightly wider than 4:3 (or only the inner 704x576 should be displayed at 4:3 DAR). The square should appear square. When following the MPEG 2 spec the entire 720x576 frame should be 4:3 and the square should appear slightly taller than it is wide.

    2) 704x576 4:3 DAR padded to 720x576 SDE704: This is the same video as #1 but with the addition of an MPEG 2 sequence_display_extension flag to indicate the 4:3 image appears in the inner 704x576 sub frame. Following either the rec.601 or MPEG 2 specs the entire frame should be slightly wider than 4:3 and the square should be square.

    3) 704x576 4:3 DAR: This uses rec.601 PAR with a 704x576 frame. With both rec.601 and MPEG 2 decoding the entire frame should render 4:3 and the square should appear square.

    4) 720x576 4:3 DAR: This program uses the implied MPEG 2 PAR. With MPEG decoding the entire frame should be rendered as 4:3. The square should be square. If rendered with rec.601 scaling the frame should be wider than 4:3 and the square should be wider than it is tall.



    The VIDEO_TS folder was burned to DVD and played on my Blu-ray player, an LG BD670, hooked up via HDMI, upscaling to 1920x1080p60. This is a region 1 NTSC player but can play PAL DVDs. The LCD TV it was hooked up to has pixel-for-pixel capability so it can display every pixel of a 1920x1080 intput (no overscan simulation). The Blu-ray player's upscaled HDMI output followed the MPEG 2 spec for all 4 videos. I was able to see every pixel of each clip (nothing was cropped).

    1) The entire 720x576 frame was scaled to 4:3 DAR. The square was rendered too narrow, measured on the LCD TV screen as 37.2 cm wide, 38.2 cm tall.

    2) The entire 720x576 frame was rendered slightly wider than 4:3. The square was the right shape (38.2 x 38.2 cm). I was a bit surprised by this. I've never seen a commercial DVD use the sequence_display_extension like this so I didn't really expect it to play properly.

    3) The 704x576 frame was scaled to 4:3 DAR. The square was square (38.2 x 38.2 cm).

    4) the Entire 720x576 was scaled to 4:3 and and the square appeared square (38.2 x 38.2 cm).

    I played the VIDEO_TS folder via a network share on my WDTV Live. This was also hooked up to a 1920x1080 LCD HDTV with no overscan simulation. I was able to see very pixel of each clip. The WDTV Live's behavior was similar to the Blu-ray player except it ignored the sequence_display_extension in #2, displaying the picture the same as #1.

    I don't currently have anything set up to test the analog output of any players.

    VIDEO_TS folder attached as a ZIP archive.
    Image Attached Files
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  19. Originally Posted by fvisagie View Post
    So it's becoming fairly inescapable that my TV display is out of spec?
    How are you connecting the DVD player to the TV? HDMI? S-video or composite? Is it a fixed pixel display (LCD, plasma) or an old CRT?
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    Originally Posted by jagabo View Post
    I had a chance to make a PAL DVD from the earlier AR test patterns.
    That's very useful, especially with your thorough description of what to expect in each case, thanks.

    How are you connecting the DVD player to the TV? HDMI? S-video or composite? Is it a fixed pixel display (LCD, plasma) or an old CRT?
    I'm using the composite output and it's a CRT display. I should maybe mention that I'm not too concerned with getting this TV to display "perfectly". I'd only been trying to use it as reference for typical analogue TV output, but when results didn't make sense I came here . With your help and that of the others I believe I've learnt enough since to be able to correctly determine input video format, to decide how that should be treated in authoring, to know what results to expect on my PC monitor and how those will translate to analogue and digital player outputs. I'm very grateful for the trouble everyone took with their contributions.

    Many thanks,
    Francois
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  21. Originally Posted by fvisagie View Post
    it's a CRT display
    There's your problem. As I noted in post #11 CRTs typically have large AR problems. Never use a CRT to adjust aspect ratios. Unless the CRT's AR was just calibrated (most have internal adjustments for AR among other things). Even then you should be careful as the AR can vary with picture brightness.
    Last edited by jagabo; 19th Mar 2013 at 06:38.
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    Originally Posted by jagabo View Post
    Even then you should be careful as the AR can vary with picture brightness.
    And I thought I was seeing things! Thanks for the confirmation.

    Cheers,
    Francois
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