A preview in the real player for any package: h5p-verify --preview #69

h5p-verify says whether a package starts. It plays the package headless and reports errors, missing libraries and what the content check would remove, with one screenshot of the first screen.

Whether the content is right is a person's call: the questions and their answers, a branching scenario's paths, the interactions at a video's timestamps, how a slide is laid out. To make that call, the person has to play the package. Today that means putting it somewhere a player can open it:

• The demo's installable app. It opens a .h5p with a double-click only when installed from Chrome or Edge, and it plays whatever player version is deployed.
• A site with the player, or an LMS upload. Both need a host, the opposite of a quick look.

An agent that generates or rewrites a package has no command that puts the result in front of the person who asked for it. That includes skills/h5p-author (PR #68), and later other content types. An answer key or scripted screenshots would have to be written for each content type, and would still show nothing of how the content plays.

Proposal

h5p-verify <package.h5p> --preview runs no check. It plays the package in the real player, in the person's own browser, on their own computer:

• The same player as the check. It uses the verifier's local server, with the same player, runtime and library sources. --untrusted, --libraries and --no-refresh-libraries mean what they mean for the check.
• Served in pieces. The package is served with Range, as a static host serves it. The libraries take a few requests and media streams by range, so a large video starts as it would on a site. Nothing is read whole or extracted to disk.
• Opens the browser. It opens the default browser on the package; --no-open prints the address instead. It works in any browser the player supports, and offline unless --libraries names a remote source.
• Stops by itself. It stops when its last tab has been closed, or on Ctrl+C, so an agent can start it in the background and leave it running.

The check stays the gate; the preview is for the person. Once the preview is released, skills/h5p-verify and skills/h5p-author will tell the agent to open it after the check.

Release

A minor of h5p-verify: an option added. In preview mode the exit code is 0 when the preview stops and 2 when it cannot start, and docs/compatibility.md will say so.