Use compressed mp4 file when available to save 98% on storage, and 99% in memory

[jtmckay]

What this does

This will setup ReRun to use the MP4 file if it is available to take advantage of MP4 compression, instead of converting every frame into a full pixel map. It will fallback to full pixels if the file is not found.

99% memory reduction in memory on the client.

How it was tested

I ran the code locally with a dataset that has mp4 files. Then commented out the part that adds the mp4, to ensure the fallback works.

Examples:

• Optimized visualize, it now runs with 98-99% less memory than previously.

How to checkout & try? (for the reviewer)

With a lerobot dataset to see disk space saved, run

python lerobot/scripts/visualize_dataset.py \
    --repo-id lerobot/pusht \
    --episode-index 0 \
    --save 1 \
    --output-dir path/to/directory

To see memory saved, run rerun (pre-req rerun-sdk) and open the .rrd file.