Function with_start_time 

pub fn with_start_time(url: &str, position_seconds: f64) -> String

Rewrite an audio-only stream URL to start at position_seconds.

Resuming re-opens the stream we were already playing, so the URL is edited in place rather than rebuilt from the repository: every other parameter — AudioStreamIndex (the track the user picked in the video player), MediaSourceId, api_key — is carried over untouched, and no network call is needed to recover from a network failure.