Fix custom video decoding

[Anudeep007-hub]

Fix: Enable decoding of custom .mp4 videos in Kinetics-style datasets

Summary

This PR introduces support for decoding .mp4 videos in datasets following the Kinetics-style directory and CSV structure.

Key Changes

• Modified dataset loading pipeline to support .mp4 files.
• Adjusted decoder logic in decoder.py for torchvision compatibility.
• Patched kinetics.py, loader.py, and __init__.py to allow seamless loading of custom datasets without re-encoding.
• Includes my_custom_dataset.py which can be reused by others for loading custom structured datasets.

Usage

You can now train SlowFast models directly on .mp4 video files using a structure similar to:

[Anudeep007-hub]

Hi! This PR enables decoding of custom .mp4 videos with Kinetics-style dataset structure. Let me know if any changes are needed. Thanks!