MP4 PAL 720x576 4:3 pixel ratio export in DVR

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KumaNatsu

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MP4 PAL 720x576 4:3 pixel ratio export in DVR

PostMon Jul 12, 2021 4:16 pm

I like to know if some one know the tech reasons why when exporting a PAL format 720x576 4:3 in mp4 (quick time or mp4 container) I get a pixel aspect ratio (aka SAR) of 59:54 (and 118:81 for 16/9 aspect ratio).
In the document ITU T-REC-H.264-201906-I
at page 389 Table E-1 specify that the aspect_ratio_idc: 2 for 720x576 4:3 frame with horizontal over scan must be 12:11 (and 16:11 for 16/9 aspect ratio). I believe in NTSC the problem is the same but I didn't check it yet.
I could not find any way to force the output of the aspect ratio look like DVR set always this aspect ratio that are not ITU H264 compliant.
Any idea? Thanks

NB: if you wonder why losing time with PAL SD format: I am restoring a "video art" video archive (1000h of video mainly in SD format), the final archival delivery will be in FFV1 but the consulting version will be in MP4 following the ITU specs, and I need to deliver some video test in the appropriate format to the consulting application developers, to solve the issue I encoded a uncompressed file with ffmpeg and the appropriate SAR but I found questionable this behavior in DVR. I remember that in the past when exporting from Flame in Prores 720x576 the exporter was setting the SAR to 181:81
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Charles Bennett

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Re: MP4 PAL 720x576 4:3 pixel ratio export in DVR

PostMon Jul 12, 2021 9:22 pm

Have you set the Timeline to that resolution and adjusted the Scaling if needed?
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Andrew Kolakowski

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Re: MP4 PAL 720x576 4:3 pixel ratio export in DVR

PostMon Jul 12, 2021 10:00 pm

KumaNatsu wrote:I like to know if some one know the tech reasons why when exporting a PAL format 720x576 4:3 in mp4 (quick time or mp4 container) I get a pixel aspect ratio (aka SAR) of 59:54 (and 118:81 for 16/9 aspect ratio).
In the document ITU T-REC-H.264-201906-I
at page 389 Table E-1 specify that the aspect_ratio_idc: 2 for 720x576 4:3 frame with horizontal over scan must be 12:11 (and 16:11 for 16/9 aspect ratio). I believe in NTSC the problem is the same but I didn't check it yet.
I could not find any way to force the output of the aspect ratio look like DVR set always this aspect ratio that are not ITU H264 compliant.
Any idea? Thanks

NB: if you wonder why losing time with PAL SD format: I am restoring a "video art" video archive (1000h of video mainly in SD format), the final archival delivery will be in FFV1 but the consulting version will be in MP4 following the ITU specs, and I need to deliver some video test in the appropriate format to the consulting application developers, to solve the issue I encoded a uncompressed file with ffmpeg and the appropriate SAR but I found questionable this behavior in DVR. I remember that in the past when exporting from Flame in Prores 720x576 the exporter was setting the SAR to 181:81


Resolve still doesn't set them properly (at leats it wasn't few months ago) and there is also a question what should be "proper setting"? It may depend what you need as there are at least few ways of flagging aspect in SD files.

Export in Resolve and then fix your metadata with this tool (there is even cmd option to run automated corrections):
http://mogurenko.com
this allows you set any values you want.
If you want "analog" flagging (502 active lines) then you set 9 for clap and then 59:54 for PAL and 8 + 10:11 for NTSC (both 4x3). For "digital" flagging which uses all pixels as active area you do 16:15 and 8:9.

59:54 is correct as long as you have clap atom (clean aperture) set to 9. This means you have active area of 720-9 pixels for each side, so 702. Then when you calculate you need 59:54 PAR to get DAR as 4:3.
If you don't have clap set then you use "digital" flagging as 16:15 (720/576*16/15=1.333)

Other solution. You export square pixels (which is modern approach). Then you just make sure you properly taken active lines from your current masters, so you keep proper aspect of 4x3 or 16x9. Quite often old masters have aspect distorted a bit anyway, so this can be a fun game to get it correct :)

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