Add durationPerFrame to Frameset

[vkay94]

• I carefully read the contribution guidelines and agree to them.
• I have tested the API against NewPipe.
• I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

This PR adds durationPerFrame field to the existing Frameset class. This property is necessary to calculate the correct frame depending on the timestamp. Before there was no way to crop the correct frame bounds from the storyboard ("framesPerPageX x framesPerPageY"-matrix).

Short example with this change to calculate the correct frame coordinates (pseudo code):

-- Goal: get frame bounds for 3:25:500 (= 180.500 milliseconds)´
-- Given: storyboard-Urls in 5x5-matrix, duration per frame = 5.000, frame height = 160 and frame width = 90

=> 180.500 / 5.000 = 36.1 => 37. Frame
=> (37 - 1 * 25) = 12 => 12. frame in 2. storyboard
=> (12 - 2 * 5) = 2 => 3. row, 2. column => row index = 2, column index = 1

=> Bounds / rectangle of the frame at the position: left top (x, y) = (0 + 1 * 160 = 160, 0 + 2 * 90 = 180)
=> (left, top, right, bottom) = (160, 180, 320, 270)

[TobiGr]

Thank you. Could you put that info into to the class JDoc so the class is easier to use?

[vkay94]

@TobiGr Okay, I'll add it. Actually, I'd prefer an open/public default implementation - something like

public int[] getFrameBoundsAt(long timestamp)

where the int-array returns left, top, right, bottom in that order. It would reduce code on the client-side.

I just checked the other services and PeerTube doesn't support frames and media.ccc.de uses the same logic as YouTube (grid) (but here you've got to load an additional vtt -file to get the count and duration per frame).

Url: https://static.media.ccc.de/media/events/rc3/150-8e6fd90f-f358-518f-95dc-19dbec1dcaea.thumbnails.vtt
Contents: https://pastebin.com/tSgFNBrV

What do you think?

[TobiGr]

Sounds good.

[vkay94]

I've added the default implementation. It should work correctly (even if the "testing" has basically been with the eyes :') )

[TobiGr]

Can be merged after this small change