How to modify MPEG2 "PixelAspectRatio_Original" value?

[mwesten]

I encountered this issue while using MakeMKV to process a DVD.
It appears the DVD author incorrectly set the vob files' aspect ratios to 4:3 when in fact the correct video playback is at 16:9.
I've not been able to find an option to fully correct this using either mkvtoolnix or ffmpeg.
Ordinarily with H264 video this is easily corrected with ffmpeg using -bsf:v "h264_metadata=sample_aspect_ratio="
I've tried using -bsf:v "mpeg2_metadata=sample_aspect_ratio=32/27"
but that returned an error as apparently that filter option for mpeg2 does not exist.

Here's the mediainfo of the video I'm working with (mpeg2 codec in mkv container)

"Width":"720",
"Height":"480",
"Sampled_Width":"720",
"Sampled_Height":"480",
"PixelAspectRatio":"1.185",
"PixelAspectRatio_Original":"0.889",
"DisplayAspectRatio":"1.778",
"DisplayAspectRatio_Original":"1.333",

I simply need to modify the "originals" to match the new override values.
If done correctly, the new mediainfo should look like this:

"Width":"720",
"Height":"480",
"Sampled_Width":"720",
"Sampled_Height":"480",
"PixelAspectRatio":"1.185",
"DisplayAspectRatio":"1.778",

[ProWo]

Use clever Ffmpeg-GUI.
Load your mpeg2 video, click main page, click various, click change DAR.
Insert 1.78, click change DAR, done.

[Selur]

I've tried using -bsf:v "mpeg2_metadata=sample_aspect_ratio=32/27"
but that returned an error as apparently that filter option for mpeg2 does not exist.

Correct, if you look at https://ffmpeg.org/ffmpeg-bitstream-filters.html#mpeg2_005fmetadata only display aspect ratio adjustments are supported.

[mwesten]

Use clever Ffmpeg-GUI.
Load your mpeg2 video, click main page, click various, click change DAR.
Insert 1.78, click change DAR, done.

Thanks, that did the trick.
I had to redo my previous 16:9 flags in mkvtoolnix to modify 1.78 to 1.778 but now I have the desired mediainfo output:

"Sampled_Width":"720",
"Sampled_Height":"480",
"PixelAspectRatio":"1.185",
"DisplayAspectRatio":"1.778",

Any idea what specifically ffmpeg is doing on the backend to make that happen?
I wouldn't mind knowing the commandline syntax for it.

[Bernix]

Just question. Isn't better to use fractions instead of insert direct values? I know there isn't basically any difference between 1,78 vs 16/9 in video but fractions are precise and not at all difficult to use them.

[mwesten]

Just question. Isn't better to use fractions instead of insert direct values? I know there isn't basically any difference between 1,78 vs 16/9 in video but fractions are precise and not at all difficult to use them.

Yeah I think that's right. I prefer 32/27 PAR and 16/9 DAR in every instance where it's allowed.
Clever FFMPEG GUI disallowed any value other than 1.78 though, much to my chagrin.
But afterwards in mkvtoolnix I reset the display values to 16 and 9 so all is well now.
Clever FFMPEG GUI performed the desired task of getting rid of whatever dumb header remnants were generating 8/9 and 4/3 "PixelAspectRatio_Original" and "DisplayAspectRatio_Original" in mediainfo.

[ProWo]

Any idea what specifically ffmpeg is doing on the backend to make that happen?
I wouldn't mind knowing the commandline syntax for it.

Selur has already shown you the solution in post #3:
Instead of
mpeg2_metadata=sample_aspect_ratio=32/27
take
mpeg2_metadata=display_aspect_ratio=16/9

Possible values are:
4/3
16/9
221/100

[mwesten]

Any idea what specifically ffmpeg is doing on the backend to make that happen?
I wouldn't mind knowing the commandline syntax for it.

Selur has already shown you the solution in post #3:
Instead of
mpeg2_metadata=sample_aspect_ratio=32/27
take
mpeg2_metadata=display_aspect_ratio=16/9

Possible values are:
4/3
16/9
221/100

I see that now.
"mpeg2_metadata=display_aspect_ratio=16/9" works exactly as needed for this situation.
Thank you both for your inputs.
Issue solved.