First and foremost, MC doesn't use images in file tags for video files. For video files MC always uses a file sitting next to the actual video file.
Okay, there can be exceptions. You could edit the [Image File] Library field manually to point to an image in a different location. Also, TV Series and Season images are held in the Cover Art location defined in "Options > File Location > Cover Art > Folder" setting. The other settings in that section relate only to Audio files. i.e. "Audio Mode" (obvious) and "Also store image in file's tag".
In the end, I used another media player to inspect the actual file tags of the 1539, MP4 and MKV video files and found each file had between three to five pieces of artwork stored in the tags.
MC used to have issues with Audio files that contained more than one image in its tags. Of course, that doesn't apply to Video files, but maybe their existence was causing MC some trouble. I think that issue with Audio files was fixed, but I don't recall the solution. You might find it in the Release Notes Wiki:
https://wiki.jriver.com/index.php/Release_Notes But it shouldn't really matter here.
Note that if, for example, an MKV file has no external Cover Art image file, the [Image File] field in MC will point to the MKV file. What MC is saying there is that the thumbnail image that MC is using was sourced from a frame in the MKV file, not that the image inside the MKV file is being used. The best way to confirm this is to right-click on the thumbnail image in MC Standard View and select "Cover Art". You will see there that the two sub-options, "View (first file)" and "Edit (first file)" are greyed out, as there is no file to view or edit, just a thumbnail based on a video frame. Thumbnails are stored separately in a Thumbnail Database MC manages.
Ironically, the majority of the artwork appeared to be stills from the video they were attached to
That usually only happens when there is no Cover Art file for a Video, so MC takes a video frame and uses that for Cover Art, as per settings under "Options > Tree & View > Thumbnails". Specifically "Capture video thumbnails at x seconds".
If you as the user takes no action, no external image file will be created in that process. However, if you right-click on the thumbnail image in MC Standard View and select "Cover Art > Save Cover Art To External Location Specified In Options", then MC creates an image file next to the video file, and names it the same as the video file except for the extension.
Has anyone experienced this before?
No. But generally I haven't used any media management tools that add Cover Art image to video files.
Any ideas as to what might have trashed these tags?
I don't think the tags have been trashed. As above, it could be that the multiple images inside tags in the video files caused an issue with MC. Now that you have removed those tags, MC should work just fine. But it may have worked fine even with them in there. I'm not sure.
If the Cover Art used to be correct, and then changed to a frame from the video, I have to assume that the Cover Art files next to the video files were deleted. If that happened, MC may continue to show the correct thumbnail of the original Cover Art file for some time, until the thumbnails were rebuilt, either when the video was viewed, or the rebuild process was run, something changed for the file and MC updated its fields, etc.
When MediaCenter removes cover art, does it remove all the art from a file or just the top file?
This was one of the issues with multiple Cover Art images inside Audio files I think, from memory. Removing Cover Art only removed the first image, not all of them. I think that was fixed and now MC removes all of them, if it can locate them. Some formats and tools put image tags in strange places, apparently. Regardless, this doesn't apply to Video files.
Could this be WMP in the background? Its literally never been run on any machine, nor has the library been setup
Well, one never knows with WMP, even when it has never been run! Unlikely though.
More likely some archiving program removed the image files next to the video files, or you did, not knowing the impact on MC. Of course, running "Remove Cover Art" will remove the files.
Try this sequence (because it is neat).
- Find an MKV file that is using a video frame as the thumbnail in Standard View.
- Check the [Image File] field in the Tag Action Window for the file and note that it is pointing to the MKV file. (Note that the field is just called "Image" in the Tag Action Window.)
- Right-click on the file's thumbnail in MC Standard View and select "Locate > On disk (external). A Windows Explorer windows will open up in the location of the video file. Note that there is no image file.
- Right-click on the file's thumbnail in MC Standard View and select "Cover Art > Save Cover Art To External Location Specified In Options".
- Check the Windows Explorer window and you will see that there is now an image file next to the video file, named the same but with a different extension. A jpg file.
- Refresh the tag window in MC and check the [Image File] field. Rather than point to the MKV file, the field will now point to the newly created jpg file, next to the video file.
- Right-click on the file's thumbnail in MC Standard View and select "Cover Art > Remove Cover Art. Click "Yes" in the popup message. You will note that the thumbnail for the Video immediately disappears. The [Image File] field in the Library now points back at the MKV file.
- Click anywhere in Standard View, or even just move the mouse over the tag window, if you still have it open. The video thumbnail will immediately re-appear. Auto Import running in the background, as per my settings, has noted the missing Cover Art thumbnail and rebuilt it from a video frame. Auto Import was triggered because the [Image File] tag is written to the file multiple times during the above process.
Neat. Enjoy!