Strange behavior with MKV crop flags

[mhendu]

Most MKV files that I've seen have the Video display width / height flags set by default (most commonly to the same as the pixel width / height). When adding crop flags (Video crop left / top / right / bottom) to the metadata MPC-BE seems to apply these flags in an unexpected way, such that the crop flags are applied first, then the display width / height flags, so a letterboxed video (black bars on top / bottom) will appear vertically stretched.

When rendering via MadVR, the player appears to create a frame with the video's dimensions, then places the video at the bottom of the frame so there's a larger black bar across the top.

What should happen (I think) is that the player should independently apply the crop and display flags to the video's actual dimensions. For example, I have some videos where the display flags were set to stretch the video horizontally, but that also have crop flags to remove black bars at top / bottom. The player should read the display flags to determine the aspect ratio, then use the crop flags to remove the black bars. This behavior should be consistent for the internal renderer and MadVR.

[v0lt]

The player does not crop the frame.
The player sets the cropping parameters (as Microsoft came up with) and passes them on to the video renderer. If you think that some video renderer is cropping the frame incorrectly, then compare the result with the result of the Enhanced Video Renderer (EVR).

There is no madVR support here.

[mhendu]

OK, maybe it's a video renderer problem. Here are a few example frames so you can see the issue. In this case the video file has display flags set to 3840x2160, with crop flags of 262 pixels on the top and 260 pixels on the bottom.

Via Enhanced Video Renderer (vertically stretched):

Via MadVR (black bar across the top):

Via PotPlayer with EVR (displays as expected, correct aspect ratio with black bars cropped)

[v0lt]

Via PotPlayer with EVR (displays as expected, correct aspect ratio with black bars cropped)

This has not been proven.

1. No one has seen your MKV sample except you.
2. There was no analysis of the parameters of your file, the MKV specification and the results obtained.

[mhendu]

Thanks, I can provide a MediaInfo export if that helps, but I do see from the specs you shared that it's expected that crop flags are applied before the display width / height is determined. The problem there is that most players don't support crop flags, but many do support display width / height flags, so adjusting the files to conform to the specs means that they won't display properly in most players. Plex, or VLC, or MPC-HC, for example, all display incorrectly if I adjust the display height to take into account a crop flag at top / bottom. PotPlayer rendering w/ EVR does seem to handle correctly, which is interesting considering that it also displays what I expect when the display flags are set to match the video resolution.

Maybe this is a behavior that the user could select in MPC-BE? That would allow the player to conform to specs but also enable it to handle these other scenarios if required.

[v0lt]

Thanks, I can provide a MediaInfo export if that helps

The MediaInfo report is no good. You need a small sample of 20 seconds (preferably up to a minute).

The problem there is that most players don't support crop flags, but many do support display width / height flags, so adjusting the files to conform to the specs means that they won't display properly in most players.

This is not an MPC-BE problem. This is a problem with other players.

Plex, or VLC, or MPC-HC, for example, all display incorrectly if I adjust the display height to take into account a crop flag at top / bottom.

MPC-HC uses LAV Filters, which does not support frame cropping.

[mhendu]

OK, thank you. I've subscribed to the request for MPC-HC, but would be great to see the ability to apply cropping secondarily in MPC-BE. If it helps to have a sample file, how would you like to receive it?

[Aleksoid1978]

Upload sample here

[Aleksoid1978]

I'm closing it because the example file is still missing.