Compare two videos

The compare tool writes qa/compare/index.html with both videos copied next to it (a.mp4, b.mp4). The page is one self-contained file with no network requests, so the folder can be zipped and sent.

1. Pick the two sides

Each of a and b is one of:

• {quality: "preview" | "final"}: this project's render;
• {project_dir, quality?}: another project's render, such as a variant or a short (absolute path);
• {file}: a video inside the project, relative to it, such as the original assets/supplied/talk.mp4 against source/assets/<asset>-tight.mp4 (the file tighten writes; its result gives the exact path);
• {reference}: a video to match, such as the piece the user pointed to: project-relative, or an absolute path only when the user gave it. The other side defaults to this project's latest render.

Give each side a short label when the defaults (quality, project name or file name) would not tell the user which is which. a is the before or reference side, and b the after side. With no sides given, the tool compares this project's preview (a) with its final render (b). If a side is missing, say which render or file is missing and offer the render skill.

2. Build the page

mcp__plugin_video-studio_engine__compare {project_dir, a?, b?}. It returns each side's label, duration and resolution, notes on differing durations or aspect ratios, and metrics[]: duration, frozen seconds and %, big changes per second, cuts per second, moving % of frames, longest static stretch and integrated loudness for both sides. Changes per second count sudden changes (cuts, reveals); moving % counts every frame where the picture moves at all, so smooth motion and crossfades show up there and not in changes/s. With a reference, each metric has a verdict (ours meets or misses the reference); summarise the misses in plain words and suggest the fix (more visual beats, motion through the holds, shorter static stretches, loudness).

3. Hand it over

You can't open a browser. Give the user the absolute path of index.html to open (on macOS: open "<path>") and tell them how to use it:

• Views: side by side, stacked, or wipe (drag the divider over the two videos laid on top of each other).
• Playback: one play button and scrubber drive both videos. Space plays and pauses, and ← and → step one frame. The shorter video holds its last frame.
• Sound: B is audible by default. Toggle each side's mute.

To say what changed rather than show it, pair this with the diff skill (spec, lock and frame changes) or review (frames you can Read yourself).