[p5.js 2.0+ Bug Report]: assigning MediaElement.src leaves stale <source> children, so reading src returns the old source

Most appropriate sub-area of p5.js?

DOM

p5.js version

2.x main (4b096e2)

Actual vs expected behavior

The src setter on p5.MediaElement removes existing <source> children with a forward index loop over the live HTMLCollection, which skips every other child as the collection reindexes:

const v = createVideo(['a.mp4', 'b.webm']);
v.src = 'c.mp4';
v.elt.childElementCount; // actual 2 (leftover b.webm + c.mp4), expected 1
v.src;                   // actual ends with 'b.webm' (getter returns children[0].src), expected 'c.mp4'

So after assigning a new source, reading v.src reports the old one, and the media element still lists the stale source first. The same code exists in 1.x, so this is longstanding rather than a 2.x regression.

Steps to reproduce

Outputs above are from executed runs against current main via the DOM unit test harness (the two new tests fail on unfixed code with expected 2 to deeply equal 1 and expected false to be true).

Note

I have a fix ready (iterate the live collection backwards, with a comment) plus 2 regression tests in the createVideo suite; the DOM suite passes 14 with it. Filing for approval per the contributing guide; will open the PR once approved.

Start with the p5.MediaElement src setter and the createVideo DOM unit test suite mentioned in the issue. Run the DOM tests, then verify that assigning a new source leaves one source child and that reading src returns the new URL; the issue notes that regression tests already exist in the proposed fix.