Incorrect aspect ratio handling

[tvasenin]

Currently, ffmpeg is invoked with -aspect 4:3 or 16:9.

This is incorrect, as 4:3 is the display aspect ratio for 922x576 (for PAL), but the output video (with default padding) is 928px wide.

The fix would be to remove the -aspect option entirely, as the correct SAR is already provided in stream header by ld-chroma-decoder:

https://github.com/oyvindln/vhs-decode/blob/d4c3f8504573b0d5cc1d1777dea7c5b69be6a161/tools/ld-chroma-decoder/outputwriter.cpp#L158

[JuniorIsAJitterbug]

You are correct, this is a mistake.
I will leave -aspect 16:9 for --force-anamorphic and --letterbox but remove for everything else.

Thank you for the report. 👍️

[tvasenin]

I will leave -aspect 16:9 for --force-anamorphic and --letterbox but remove for everything else.

In these cases, it's still incorrect to pass -aspect 16:9, as the resulting AR will be wrong due to the padding (and potential vertical crop overrides).

You should override SAR instead, as per the code above:
PAL Widescreen: -vf "setsar=512/461:max=1000"
NTSC Widescreen: -vf "setsar=194/171:max=1000"

(max=1000 option is required, otherwise ffmpeg will try to lossy-reduce the ratio to make numerator and denominator become <= 100)

[JuniorIsAJitterbug]

Great, thank you for the information.
I've tested the values you sent and I think the PAL values should be swapped?

setsar=194/171:max=1000 = 1052x432 2.44
setsar=171/194:max=1000 = 928x490 1.89
setsar=97/114:max=1000 = 760x394 1.93

[tvasenin]

No, it shouldn't be swapped, as this is SAR (sample aspect ratio aka 'the shape of the pixel'), not DAR.

If you want to understand how it's derived, take a look at the source code above.

[JuniorIsAJitterbug]

Understood.
Does the code above not use the following?

PAL 16:9 = 512:461
PAL 4:3 = 384:461
NTSC 16:9 = 194:171
NTSC 4:3 = 97:114

Apologies if I've misread this again. 🙂

[tvasenin]

Yes, these values are correct.
It was wrong copy-paste on my side -- updated my post.

[JuniorIsAJitterbug]

I have added the 16:9 setsar values when --force-anamorphic and --letterbox are used.
-ar usage has been removed.

I hope this is now solved. 👍