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Handling non-square pixels, render still square

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Linwood Ferguson
Handling non-square pixels, render still square
on May 15, 2015 at 3:06:30 pm

I am very new to video, long time still photographer, and was attracted to Resolve for its color handling, but struggling with the quirks of video.

I have a stack of SVHS videos I shot in the 1980's, which were digitized 10 years or so ago to DVDR's, and want to edit and get them on disk and archived in my general catalog, and where I can show people.

I have no specific target format I need to hit (well, ultimately MPEG4), but had thought to maintain approximately the same resolution, and want the same aspect for the final result of course. The simplest seemed to be to maintain the same size throughout. I did some test conversions with Handbrake that worked nicely to MPEG4 via H.264 (though obviously not edited).

When I render from Resolve Lite, I get square pixels, and a squished display, no matter what I try.

When using Resolve with 704x480 projects, I can only choose square pixels, so I switched to NTSC which defaults to 4:3 (it calls it pixel aspect but I assume that's DAR, with 10:11 pixel).

Here's the latest thing I tried:

1) transcode DVDR with FFMPEG to Prores 422, maintaining scale.

Both media info and playing the result shows the proper DAR of 4:3 and looks correct.

2) Create a Resolve project with NTSC, confirm it says 4:3, ensure the timeline and monitor and render are all set the same.

3) Bring the converted Prores clip into the media pool

I notice the pixels show up there as square under clip attributes; I've tried both changing to NTSC and leaving square - one crops the image, one doesn't, but neither result in a different SAR on render.

I should note I think things are already going wrong here as they media player in resolve is about 3:2 when shown 100%, so I think it's already wrong at this point.

4) Deliver (render) to NTSC, leaving mostly defaults, notably 720x486

4a) I tried MPEG with its defaults
4b) I tried H.264 with its defaults

In all cases the result in mediainfo shows 720x486 as expected, but with a 3:2 DAR and so 1:1 pixel aspect. When played, they are squished flat. Note at least with NTSC pixels in the clip attribute there's no black bands on top or sides of the result, it's the whole frame, just the specified square pixels cause the player to squish it.

There's no setting on output I see for specifying SAR or DAR, I would assume it is picked up from the project (which I confirm still shows 4:3 SD.

I feel like I'm missing something. Is Resolve simply not able to handle non-square pixel output? Isn't NTSC (which is supports apparently) always 4:3? Should I output some other format, then use a different render to produce the final MPEG4?

Should I scale 1.1x on input with FFMPEG and use square pixels there, then create some custom resolution to match (704x528 I guess)? I assumed creating something non-standard may make it more difficult to play later.

Or can I copy with FFMPEG (not re-encode) and just specify SAR?

I've figured out most things otherwise - I've got titles and lots of different transitions (experimenting) and clipped out stuff and cleaned up and fixed gross yellow and washed out beach scenes to be at least reasonable and feel like I have a handle on most things.

And editing my DSLR video is a snap as it's nice square pixels.

I just can't get a handle on the proper approach to handling these vintage DVDR's of SVHS. A few pointers would be most welcome.


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Linwood Ferguson
Re: Handling non-square pixels, render still square
on May 17, 2015 at 9:04:51 pm

Hopefully my post wasn't inappropriate in some way, if so I apologize and please help me know why.

But in case someone else is helped with this, here is what I ended up doing.

First, nothing I tried in Resolve's deliver function produced a file with 4:3 DAR even when it was set for it. Whether that's my error or a "feature" I do not know.

So what I did was maintain a 704x480 resolution throughout (explicitly, not choosing NTSC), used square pixels inside of Resolve, and did a change after output.

1) From DVD: Used MakeMKV to copy the DVD to disk as MKV file and consolidate the individual containers.

2) Used FFMPEG to convert from MKV to Prores so I had a more edit friendly format in the same size, and also de-interlace (experiments each way showed this to be better). Example command:

ffmpeg -i "u:\Videos\Hawaii_1988\title00.mkv" -vf yadif -codec:v prores_ks -profile:v 2 -qscale:v 11 -c:a pcm_s24le "u:\VideosToResolve\Hawaii_1988.mov"


3) Used the above for input to a Resolve, in a project with timeline explicitly set to 704x480 square, 29.97 frame rate (matching the original).

4) Edited, color corrected, etc.

5) Rendered from Resolve as an uncompressed intermediary file. I chose more or less at random (advice welcomed) Quicktime, Uncompressed UYV 422 8 bit, 704x480, 29.97 with audio.

6) Converted to a more web/PC criendly MP4 format with FFMPEG as follows:

ffmpeg -i "u:\VideosFromResolve\Hawaii Test Output.mov" -c:v libx264 -preset veryslow -crf 18 -maxrate 1500k -bufsize 1835k -refs 3 -pix_fmt yuv420p -vf "setsar=10/11" -c:a libvo_aacenc "u:\VideosOut\Hawaii Test Output.mp4"


The result is, as expected, pretty sensitive to the maxrate parameter; I found I could not see a difference at 1.5mbs vs the original input of about 4.3mbs and saved a lot of space (these old sVHS were really messy).

The other thing I had was about 8 pixels of tracking error noise at the bottom. I've experimented with both blanking it out, and also zooming to shift it off screen at the bottom (avoiding a black bar at the bottom). I'm not sure which is better -- the slight zoom scale is probably distorting slightly, the bar is a nusiance.

The result of this is a MP4 that expects a 10:11 pixel width which all the players seem to respect (though some scale horizontally some vertically, interestingly).

I still don't know if I would have been better to scale this on input into square pixels so that on output I actually write 704x528 pixels square. That seemed to work, but again not sure if the scaling is better done there or let the player do it.

Advice welcomed, I don't know if I'm creating something needlessly complex or not. But it works.

Linwood


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