bug(YoutubePlayer): `startSeconds` input value is ignored with `disablePlaceholder` and `playerVars` containing `autoplay: 1`

[itotallyrock]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

The YouTube player ignores the [startSeconds] input when disablePlaceholder and playerVars has autoplay: 1 set.

Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-utmzdvjd?file=src%2Fmain.ts
Steps to reproduce:

1. Have a valid <youtube-player> element with working videoId
2. Set disablePlaceholder to true
3. Set startSeconds="N" where N is a non-zero value.
4. Set [playerVars]="{ autoplay: 1 }" to automatically start the video.

Expected Behavior

The video to automatically start at N seconds.

Actual Behavior

The video automatically starts from the beginning.

Environment

• Angular: 21.0.3
• CDK/Material: 21.0.3
• Browser(s): Chrome 143, Firefox (with autoplay allowed) 143, Edge 143
• Operating System (e.g. Windows, macOS, Ubuntu): Windows