Add fps argument to export_to_gif function.

[masaishi]

What does this PR do?

This PR introduces an fps (frames per second) argument to the export_to_gif function in the Diffusers library, with a default value of 10 fps. This feature allows users to specify the frame rate of the GIFs they generate, providing greater control over the animation's speed.

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@patrickvonplaten @DN6

Reference

Pillow documentation

duration
May not be present. The time to display the current frame of the GIF, in milliseconds.

[DN6]

Okay to add the FPS argument, but I think you get unexpected results setting duration in this way. e.g. You have 100 frames, and you set FPS to 10. One would expect a 10 second GIF. But what you actually end up with is a 100 millisecond GIF.

Duration should be calculated with something like:

duration = (len(images) // fps) * 1000

Or optionally we provide a duration argument that defaults to 100 milliseconds and the FPS argument can override it

[masaishi]

Thank you for reviewing.

Since duration can specify the number of seconds in ms to display one frame, I think it will work correctly at 1000 // fps.

I attached gifs I actually tried my code at fps 1 and 10. I generated 16 frames by PIA example code.

1 fps -> 1000 duration

10 fps -> 100 duration

[DN6]

Ah okay. Misunderstood how duration was applied. Looks good to me 👍🏽

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