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 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.I was telling him the proper way if he wants a 720x576 frame.
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
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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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...
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. -
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 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? -
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 -
This is how that sample you refer to displayed here:
which - of the 3 tests in the last sample I did above - corresponds exactly with this particular one
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 07:32.
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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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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.
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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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:
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.Last edited by jagabo; 18th Mar 2013 at 10:10.
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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
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 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? -
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. -
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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?
Many thanks,
Francois -
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 07:38.
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