How does Plex create the Video preview thumbnails?

General Discussions Plex Features
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Hey guys I have a question about how video preview thumbnails are created. Does Plex analyze a video frame by frame and uses numbers in a particular order (for example every frame number 10, frame number 20, etc.) as preview thumbnails or does Plex store the frame after a number of time (the frame that’s shown let’s say after 10’000ms is used, next frame after 20’000ms and so on),

And I guess there is no way it can be changed manually (for example if a thumbnail looks blurry or something).

Thanks in advance. :slight_smile:

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You can control the rate at which thumbnails are created using the advanced setting GenerateBIFFrameInterval. Its default value is 2, so preview thumbnails are generated every 2 seconds. Setting this to a higher value can significantly reduce the amount of thumbnail data written to your Plex data folder, thus reducing its total size.

As noted in the linked thread, this only affects future thumbnail generation. So, if you’d like to have your existing media regenerate using the updated value, you’ll have to delete the current thumbnails.

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Regarding OP’s question - are you referring to Video Preview Thumbnails? Sometimes people use that term when they’re really asking about Posters. :slight_smile:

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VPT thumbnails are extracted on a time interval, but (for extraction performance) only the encoded video’s keyframes are considered.

Some of the ffmpeg options used are mentioned here:

Video Preview Thumbnail Generation Fails for Some Items - #15 by Volts

If you felt crazy, it would be possible to manually extract the images, edit and customize them, generate the .bif file, and store it.

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Hey guys thanks so much. I really Appreciate it! :slight_smile:
Maybe my question was a bit confusing. My idea was to increase the preview frame rate of a single video.

For example: a cat runs and jumps for a for a toy prey and I want to show the moment of the catch. In this case the frame every 2 seconds are way to slow and you see many claws but no prey. :wink:
Because in a Movie with 2 1/2 hours you find a specific scene pretty fast and usually the 2 seconds refresh rate are enough and there is no reason to increase the rate and waste storage.

Exactly. :slight_smile:

@trumpy81
I know it’s not Christmas yet but my wish for situations like this is a Plex specific configuration file similar to .plexignore (let’s call it .plexconfig for now :slight_smile: ) where you can add some tuning values.

Let’s say our video is here:
/Media/pet videos/cat jumping.mp4

then add the config file
/Media/pet videos/cat jumping.plexconfig

In cat jumping.plexconfig you set the parameters like this:

file name= "cat jumping.mp4"

refresh rate= "0.5"

Now it would refresh the frames every 0.5 seconds for this specific video.

(And for a slow moving ship video I could set the number to 2 or 3 and save some storage). :wink:
Thanks again!

I don’t know if there is a “feature request” thread already with a similar topic.

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I’ve never investigated how low it can go!

A half second is the default, but it’s dependent on there being enough keyframes present in the video, and that’s not always true. Follow that other thread I linked for a way to force it to process every frame and guarantee 0.5s preview frames.

But I know some clients (Roku) don’t even go down to the half second default. Web and ATV do leverage 0.5s previews.

Below 0.5s or 1s … like, just start the video, dude. :slight_smile:

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