P: Read and write video metadata into video or sidecar

Lightroom Classic does not write metadata to videos such as keywords and captions. Whenever I come across a video I want to add a keyword to in Lightroom, I have to move it to an empty folder so that Bridge doesn't have to generate thousands of previews (something it doesn't do anywhere near as fast as LR) and then keyword the video. Since Lightroom can't read updates, I now have to re-import the video. This takes up extra time. Can you let LR read and write metadata for videos, like you do for photos? Even if you export a video in LR and check the box that says to write keywords to the video, keywords aren't written to the video. Just found that out today, as I continued my search for a solution of LR changing file's creation dates whenever I keyword or caption photos and save the metadata.

LR 7.4 added support for HEIF / HEIC photos, whose format is based on the same Quicktime format as MP4 videos.  Even though that format supports writeable metadata, Adobe decided to write the metadata for .heic photos to .xmp sidecars.  Too bad they didn't write the few extra lines of code to do the same for videos.

I use Lightroom to import all my photos and videos onto my computer and I'm finding the lack of communication between Adobe programs rather frustrating. The keywords function in Lightroom works well within Lightroom, but if I tag videos within LR and then try to use the same videos in Premiere Pro the keywords don't carry across, and this really slows down my workflow in terms of video editing.

For videos (and photos too) we need a keywording system that applies the keywords to files at the root level so they're accessible within any Adobe program. It would save so much time having to label footage every time I use particular clips in a new Premiere Pro Project, and also make cataloguing of footage so much easier than the mess it is now.

I'd like to add my support to the idea that Lightroom add the ability to export metadata to a sidecar for movie files. Bridge seems able to save metadata in some movie files directly, but a sidecar file would be better for my needs. If this is a possible addition to Lightroom, I'd really like to see it added in soon.

Yes!  Yes!  Yes!  I have to imagine that this is coming soon!

"So I copied the image & movie files back (thankfully I keep a backup on a Drobo). I then restored a catalog backup. What seems to have happened is my movies all lost there creation dates."

If you're referring to the file creation dates shown in the Mac Finder, not all programs maintain those dates as you copy files.  It's very possible that whatever utility you used to backup or restore the files lost the file creation dates.  (A program has to take explicit action to maintain them -- the operating system doesn't do it for them.)

There are so many programs these days that don't maintain file creation dates that, in my opinion, you shouldn't rely on them.  Better to rely on the metadata fields stored in the image or video.  (Except of course, LR can't update such fields.)

XMP metadata can be stored inside a file if the file format supports it (as most do), otherwise it can be stored in .xmp sidecars.  For photos, LR stores XMP metadata inside JPEGs, TIFFs, PNGs, and PSDs.  For proprietary raw files, LR uses .xmp side cars.   The information stored in the XMP metadata is the same in both cases.   

The same approach can be used with video.  As described in that spec, XMP can be stored inside the video for the common formats and in .xmp sidecars for other formats that don't allow it.

The XMP spec allows all of the EXIF and IPTC metadata fields to be stored inside XMP.

Okay, the document you reference, http://www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMPSpecificationPart3.pdf,  looks useful for programmers. It  takes a wider view of XMP, beyond the IPTC type of information we users are typically want to enter on our own.  It doesn't address the question that it appears Adobe doesn't support transport of IPTC XMP metadata associated with video files outside of its stand alone applications. IPTC metadata may be entered within Lightroom, Bridge, etc. but I haven't seen a way to transport the metadata to another application, computer, user, etc. Photo Mechanic does this with an XMP sidecar file, but I have yet to find another application that does. Of course it takes another application to be similarly programmed to read the associated XMP sidecar files. I found Canto Cumulus successfully does. I'm not sure what other applications do.

The XMP Specification Part 3: Storage in Files (an Adobe document), specifies how to store XMP metadata in: ASF (WMA, WMV), AVI, FLV, MOV, MP3, MPEG-2, MPEG-4 (generic and F4V), SWF, WAV, AVCHD, P2, Sony HDV, XDCAM EX, XDCAM FAM, XDCAM SAM.