Video files

Converting the 3 Schweinehunde podcast turned up two episodes with <video> tags in their shownotes. q.e.d. escapes raw HTML in Markdown, and the Video block only knew YouTube, Vimeo and PeerTube. So the block got a second source (#127): a file in assets/, the Downloads tab.

The browser already has a player

No library is needed to play a video: HTML has one built in.

<video controls playsinline preload="none" src="../assets/finish.mp4"
       poster="../media/finish.jpg">
  <a href="../assets/finish.mp4">Ins Ziel</a>
</video>

controls shows play, time and fullscreen. preload="none" loads nothing until a visitor presses play, so a page with a video stays as light as one without. The poster (the block's image) fills the space until then. Without a poster, q.e.d. writes preload="metadata" instead, so the browser fetches just enough to show the first frame. The link inside is for browsers that can't play video at all. See MDN on <video>.

A match arm that needs a value: if let guards

render_block in crates/qed-core/src/generator.rs has one big match over the block types. The Video block now goes two ways: a file if there is one, the platform link otherwise. And "there is one" means more than Some: the field may hold only spaces. A match guard puts a condition on an arm. With if let, the condition can also unpack a value:

Block::Video(video)
    if let Some(file) = video
        .file
        .as_deref()
        .map(str::trim)
        .filter(|f| !f.is_empty()) =>
{
    RenderedBlock::VideoFile {
        src: download_location(file, links, root).0,
        // …
    }
}
Block::Video(video) => match video.url /* … */ {
    // the platform link, as before
}

When the guard doesn't match, Rust tries the next arm, the old Video code. And file exists only inside the arm whose guard bound it. Without the guard, the first arm would have to hold both cases in a nested match, one level deeper.

Elixir has had this forever: a case clause or a function head can pattern-match and carry a when guard. Rust's plain if guards are the same idea. if let guards go further, because Elixir's when can't bind new names. They became stable Rust only recently; see match guards in the Reference.

Two players on one page

The Latest episode block now shows the Podlove Web Player, like episode pages. On an episode page whose layout includes a Latest episode block, that makes two players, and the page loads q.e.d.'s player.js twice. The script starts every player it finds, so running twice would start each one twice. The fix is a flag on window at the top of crates/qed-core/assets/player.js:

if (!script || window.qedPlayerStarting) return;
window.qedPlayerStarting = true;

Scripts on a page share window, so the second copy sees the first copy's flag and stops.