Video frame references

[emilk]

Implement design from:

• Design for "Video Frame References" #7272

Data model

/// Maps a time point in a video to one or more Rerun timelines.
// TODO: a better name (we're reference a video _time_, not a frame)
component struct VideoFrame {
    /// References the closest video frame to this time.
    /// (closest-to instead of latest-at to forgive rounding errors)
    video_time: i64,
    
    time_mode: VideoTimeMode
    
    /// Reference to an entity with a `VideoAsset`
    /// (OR to an entity with a BlobURI in it, for extra indirection)
    // null = self
    video: Option<EntityPath>,
}

enum VideoTimeMode {
    PtsNanoseconds, // Overkill accuracy for future proofing

   // Save for future: FrameNr
}

SDK

Our logging SDK should had a helper for generating all VideoFrame for a video.

mp4_blob = load_file("foo.mp4")

rr.log("video", VideoAsset(content=mp4_blob))

# Be explicit:
rr.send_columns("video",
    capture_time=[10.0, 10.16, 10.33, 10.50],
    [VideoFrame(ms=0), VideoFrame(ms=16), VideoFrame(ms=33), VideoFrame(ms=50)]
);

# Or use our helper function:
rr.send_video_frames("video", mp4_blob, capture_time=10.0)

Viewer

Our VideoVisualizer queries for VideoFrame.
We follow a VideoFrame via another latest-at query on the given entity path.

A VideoAsset without VideoFrame will not show up in any space view.

Selecting a video should ideally show that video in the selection view (with independent playback).
It should also be able to show the actual frame timestamps in the video.