Correction of FrameUtility

[moi15moi]

Finally, this should be the last version of FrameUtility.
For reference, here is the previous version: #37

Why it is needed?

The previous FrameUtility would not work with VFR video, now yes.

Finally, the previous FrameUtility was more a hack than anything else. Now it relies on the same algorithm as Aegisub.

What has been done?

• Add TimeType Enum
• Add decord dependency
• Be able to create Timestamps with 3 methods (from_fps, from_video_file, from_timestamps_file)
• Correction how to convert ms to ass_timestamps
• Correction of the algorithm of ms_to_frames and frames_to_ms
• Add some tests

How to get the timestamps from an video?

I did some test with multiple library.

• decord
• ffprobe
• MoviePy
• PyAV
• pyffms2
• OpenCV

I choose to use decord, because it was the second fastest and it is easy to install compared to some of them like pyffms2.
ffprobe is the best, but it need the user to have installed FFmpeg.

Important to note, decord seems to automatically normalize the timestamps.

Here is the script I used to compare all the librairies: Get timestamps.zip

Here is how much times it took to get the timestamps for an mkv of 24 minutes:

With Movie py 0.65625 seconds
With cv2 2.4375 seconds
With ffms2 0.0625 seconds
With decord 0.03125 seconds
With av 1.28125 seconds
With ffprobe 0.0 seconds

[moi15moi]

Superseded by #48