Generate cover image

[WithoutPants]

Resolves #9

Note: this change also moves the scan/generate/import/export operations from query to mutation, since these are mutating operations. This will impact external scripts using these operations.

Adds a new tab to the scene page - Operations. Within this tab, there are two buttons. One generates the cover image for the scene based on the current position of the scene player, the other generates the cover image using the default settings.

Note that a page refresh may be required to see the updated images after generation, due to caching.

[bnkai]

Is this WIP?

First by changing the operations to mutation i get this Invariant Violation: Invariant Violation: 10 (see https://github.com/apollographql/invariant-packages) when i try to run any changed operation from the settings panel ( scan , autotag , generate)

Also you are using ( in generateImageAt) the generator from the previews task that was supposed to generate the previews and the webp for the wall view not the screenshots. This leads to this error when trying to "create a thumbnail"
ERRO[0084] ffmpeg error when running command </usr/bin/ffmpeg -v error -ss 272.40798 -y -i /edited/path/to/filename.webm -vframes 1 -q:v 1 -vf scale=640:-1 -f image2 /edited/mystash/meta/tmp/b33cb3c05a5ba5b017573a43fdb1e74e.webp>: [image2 @ 0x55c5e91be700] Could not get frame filename number 2 from pattern '/edited/mystash/meta/tmp/b33cb3c05a5ba5b017573a43fdb1e74e.webp'. Use '-frames:v 1' for a single image, or '-update' option, or use a pattern such as %03d within the filename.

which is because you are using image generate options (-f image2) that are not compatible with webp (g.ImageFilename).
The paths also are not the correct ones for the screenshot and the thumbnail generation is missing also...

The screenshots code should work like task_scan.go->makeScreenshots
take the outputpath of the screenshot image (normalPath in the makeScreenshots code ), thumbnail (thumbPath) and put it to the options.outputPath before calling the encoder. This changes the output file to jpg instead of the webp now and also works directly at the screenshots directory (we don't need / use an intermediate tmp dir for the screenshot,thumbnail generation)

[bnkai]

The screenshot / thumbnails generation seems to work fine.
A point to consider though. If the user wants to have a custom screenshot shouldn't this screenshot also update the cover in the DB ? Otherwise it will not be exportable. This also affects the consinstency of the cover image function.
If you make a new screenshot while there is a cover in the DB then the screenshot gets generated fine and all the images you see in the UI including the cover one are from that screenshot. The cover image is still in the DB but nowhere to be seen.
IMHO when the screenshot changes then the cover ( if it exists in the DB ) should be in sync with it.

[WithoutPants]

Yeah, you're right. The earlier version did that, but forgot to port that in during the rework.

[WithoutPants]

Added setting image in the database and ported to 2.5 UI. Ready to review.

[bnkai]

Tests ok for me (default,custom,thumbnails,db) , both v2 and v2.5