[HELP] Add MKV Metadata Crop and Aspect Ratio

[Analog]

see: https://mkvtoolnix.download/doc/mkvmerge.html
-> Shouldn't SMPTE 170M be BT.470?

SMPTE 170M is a late standard that doesn't correspond with most pre-1990's recordings, while BT-470(M) is a new name for the old FCC standard that has been used since the 1950's. White points, color coordinates, & gamma curve are surprisingly different... See: Wiki https://en.wikipedia.org/wiki/RGB_color_spaces , the 470M standard https://www.itu.int/rec/R-REC-BT.470-6-199811-S/en , and the SMPTE standard (which is part of BT.1700) https://www.itu.int/rec/R-REC-BT.1700-0-200502-I/en

Different versions of Rec. 601 reference different chromaticities, with older ones (pre-1990s) using the FCC system & newer ones defining SMPTE 170M...

This is quite confusing and terrible. I've only really started understanding this the last few weeks myself. It doesn't help that the "Matrix" calls it FCC, "Transfer Matrix" calls it "Gamma 2.2" (which is kind of correct but...ugh), and the "Primaries" are referred to by BT.470M... However, they all are the 4th option in the list, probably for a reason. I wonder if a couple different, unrelated people wrote the documentation.

I'm not even sure if any players internally handle 170M and 470M differently, even though they should. I'd certainly like the information automatically stored in the file for my non-170M recordings...and maybe noting that these selections all are related to (the readily available standard) BT.470 might be most helpful.

Looking at the documentation, there is no DAR signaling. (Hybrid does already signal the PAR through '--aspect-ratio-factor'.)

Also not sure which players support the crop signaling. (last I checked only vlc supported it,...)

Please search for DisplayUnit here: https://www.matroska.org/technical/elements.html
MKVToolNix does support it. I've used it a lot. They call it "Video display unit" under the Header editor or the Muliplexer lets you set DAR under the "Video properties tab" (called "Set aspect ratio")

...I haven't found a player that supports it crop signaling yet (I haven't even seen it work with VLC), but, once again, I'd certainly like the information stored in the file if possible...

DVD, DV,... all use anamorphic aspect ratios, so it was kind of the norm until internet streaming and Blu-rays (which still use anamorphic for quite a few resolutions). 

Assuming the content you have has a proper set PAR (pixel aspect ratio) and is displayed properly before conversion, just setting the crop values should be the enough.
Assuming the content you have has a wrong PAR value and thus is displayer wrongly before conversion, why would you want to keep that wrong value?

Two edge cases!

• I work with early HD recordings (pre-1996) which are odd 1920x1035i @ 16:9 or ~1800x1035i @ 5:3. Modern capture equipment captures it all as 1920x1080i with an extended blanking period. It can't be cropped to 1035 since it's not divisible by two/four. Also, real cropping of interlaced content just hasn't been a great experience... It would be great to just crop and force to 16:9 or 5:3 in metadata for archival... It should all work together as a post processing effect assuming a player adds support one day! (Will put some feature requests in  ) However, currently, I've been doing this manually when deinterlacing and actually cropping videos for YouTube...which always results in an odd aspect ratio. At that point I go into MKVToolNix and set the appropriate AR and, when uploaded to YT, YT respects the DAR. (Maybe others might exploit it for interesting wide effects?) I understand that this could be done via PAR but... it's less computationally intensive for me, more so for Youtube.
  
• Similarly, if I want to eliminate overscan/head switch noise on, say, VHS captures, I can still force it to display as 4:3 even with an odd crop. Almost all players respect DAR settings...