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IDProjectCategoryView StatusDate SubmittedLast Update
0002817KdenliveUser Interfacepublic2012-11-05 19:162012-11-05 19:16
Reportergaelsano 
Assigned To 
PriorityhighSeveritytweakReproducibilityalways
StatusnewResolutionopen 
PlatformALLOSALLOS VersionALL
Product Version0.9 
Target VersionFixed in Version 
Summary0002817: Project Settings, resolution, aspect ratios
DescriptionCreate Profiles for MPEG-2 4:3 Aspect Ratio and 16:9 Aspect Ratio with 704x480 pixels and 704x576 to accommodate ATSC and MPEG-2. And a 720x480 pixel profile with 10:11 and 40:33 sampling aspect ratio to accommodate ATSC and H.264.

MPEG-2 demands DARs of 4:3 or a DAR of 16:9. DVDs only subscribe to DAR 4:3 and DAR 16:9. Since DVDs are 720x480 resolution, DVDs don't follow the 13.5 MHz sampling correctly. Given the timing of analog playback only 702~711 pixels can ever be transmitted. But digital connections must do a direct re-size and use all pixels. SD video only uses 704 pixels but film DVDs use all 720. ATSC avoids this ITU-DVD Sample Aspect Ratio conflict by using 704x480.

H.264 uses a constant pixel-sampling aspect ratio. Now sources with 720 horizontal pixels would be stretched to 655 then optionally cropped to 640 pixels, or stretched to 640 pixels directly. (873->854 for widescreen). ATSC avoids this crop-nocrop dilemma by using 704x480.

#1) H.264 does not allow a Sampling Aspect Ratio of 8:9 nor does it allow for Display Aspect Ratios. 0000002) MPEG-2 is used at 704x480 and 704x576 resolutions quite often though not on DVDs.
Steps To ReproduceTry to start any project and set the profile.
Additional InformationI've read through as much DVD material you can get without subscribing to the DVD forum and scoured forums of videographers, editors, broadcasters, Adobe, Sony, et al. I've pored over the materials for H.262/MPEG-2 (used by DVD), and H.264/AVC and ITU Rec 601 (SDTV) and Rec 709 (HDTV), the Blu-Ray specifications, and more. They use Sampling Aspect Ratio (SAR) in the terminology.

The active line length is 53.33 microseconds This meant that, of those 720 samples, only 711 samples had video data in them under 525/60 systems and 702 samples under 625/50 systems. 525/60 systems ceased using the top three and bottom three "visible" lines. 711x486 systems soon cropped to 702x480. Technically a latter day NTSC broadcast had a 711x486 signal with the top 3 lines and bottom 3 lines blank and the leftmost 5 pixels and the rightmost 4 pixels blank as well. To maintain a 4:3 aspect ratio, only the center 702 pixels were used. Hence an "active" image area of 702x480 or 702x480.

Why capture at 720x480 and 720x576 under D-1? It was best to capture too much and crop later. 720 pixels only existed for old capturing equipment like D-1 which needed to oversample the unstable analog broadcast signals. After calibration the machine would recenter the pixels but only 704 pixels would be used in the re-transmission due that 13.5 MHz timing. Whether or not those padding pixels were cropped before re-transmission, the pixel aspect ratios were roughly 10:11 (and not 8:9) for 525/60 systems. If you did not crop the pixels before analog transmission on a 13.5 MHz signal, then the TV would simply ignore them since they were transmitted in a "dead" zone after the sync pulse but before the TV would accept video signals and begin scanning. The TV would simply ignore any information given to it in this time-frame.

DVDs sourced from DigiBeta or analog were sampled at 13.5 MHz had about 702 horizontal pixels of active area and 18 pixels of near black. These DVDs would ideally get a SAR of 10:11 or 40:33 and a DAR of 15:11 or 20:11. The picture would be cropped during analog transmission if the output card's signal ran at 13.5 MHz. If the signal were digital, the monitor could display an image with a DAR that was slightly wider than "normal" with thin dark bars at the sides or the monitor could crop those bands. DVDs sourced from film usually used all 720 horizontal pixels upon resize. These DVDs would ideally get an SAR of 8:9 or 32:27 and a DAR of 4:3 or 16:9.

MPEG-2 only permitted DARs of 4:3 and 16:9 and 2.21:1 exactly or a SAR of 1:1, and DVDs didn't allow anything other than 720x480 to be available in widescreen, so we got 720x480 with a DAR of 4:3 or 16:9 exactly (PAR of 8:9 or 32:27 or 16:15 or 64:45).

ATSC's implementation of MPEG-2 has side-stepped the whole issue by using 704 horizontal pixels. This meant no horizontal blanking at the edges of the signal. A straight resize of DAR of 4:3 or 16:9 results in 640x480 or 854x480. A faithful SAR of 10:11 also resulted in 640x480 or 854x480.

For H.264/AVC the ITU and ISO got their stuff together and looked at the original ITU Rec. 601 again. They decided that NO DAR would be used. From now on, it was SAR only. The available choices included 1:1, 10:11, 40:33, 12:11, 16:11 and others to accomodate for other resolutions (like 20:11 and 24:11 for 352 pixel images, and 4:3 for 1920x1080 downsampled to 1440x1080).

This meant that 704 pixel wide images would have a SAR of 10:11 or 40:33 resulting in happy 640x480 and 854x480. 720 pixel wide images and 480 pixel wide images are explicitly labelled in the handbook as having "horizontal overscan" (actually horizontal sampling). This means that when these get stretched out, they result in 654x480 and 874x480.

This ratio for SVCD is in H.264 and in Kdenlive. Hurray! Kdenlive acknowledges that 480x480 with a Sampling Aspect Ratio of 15:11. This results in an image with DAR of 15:11 and the wizard lists it as 4:3 exactly, but no matter, the project is at 480x480 with the correct Sampling Aspect Ratio.

So... why can't I make videos with 720x480 with a SAR of 10:11 and 40:33 under H.264 in the Project Settings? Why can't I make a MPEG-2/H.264/ATSC compliant project with 704x480 resolution?

***

SOLUTION: Add project settings for

+ ATSC-SD that is 704x480 with an SAR of 10:11 and DAR of 4:3 (Rec 601 Color)
+ ATSC-SD Wide that is 704x480 with an SAR of 40:33 and DAR of 16:9 (Rec 601 Color)
+ Blu-Ray NTSC that is 720x480 with an SAR of 10:11 and DAR of 15:11 (Rec 601 Color)
+ Blu-Ray NTSC Wide that is 720x480 with an SAR of 40:33 and DAR of 20:11 (Rec 601 Color)
+ Blu-Ray PAL that is 720x576 with an SAR of 12:11 and DAR of 15:11 (Rec 601 Color)
+ Blu-Ray PAL Wide that is 720x576 with an SAR of 16:11 and DAR of 20:11 (Rec 601 Color)

~ SVCD NTSC that is 480x480 with an SAR of 15:11 *and a DAR of 15:11* (Rec 601 Color)
~ SVCD PAL that is 480x576 with an SAR of 59:36 *and a DAR of 15:11* (Rec 601 Color)

***

Also, none of this has anything to do with overscan. That is a phenomenon caused not by analog sources but by the Cathode Ray Tube. All TVs too could be adjusted to "zoom" out, but that created an ugly pincushion effect as the light bent inward on dark scenes. Sampling 720 pixels is about oversampling. An analogue transmission is not nonstop waveforms. There are gaps. The CRT or the LCD TV or whatever will ignore any noise or waves that appear in these windows (measured in micro seconds).

If I've explained this all too poorly, check out http://lipas.uwasa.fi/~f76998/video/conversion/ [^] and anything by "edDV" on http://videohelp.com. [^] If you check out the Adobe Premiere forums, there was a bit of confusion about this among users when it finally got corrected in CS4 and there was also some confusion when they sorted out the 601 and 709 colour spaces in CS 5.5.
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Build/Install MethodDistribution package
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Date Modified Username Field Change
2012-11-05 19:16 gaelsano New Issue


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