🐛 Fix YouTube streaming black screen by passing HTTP headers to VLC

[WilliamTahar]

Summary

YouTube streaming mode (MODE_STREAM) currently results in a black screen because VLC does not send the HTTP headers required by YouTube (notably User-Agent and Referer). This PR extracts HTTP headers from yt-dlp and forwards them to VLC using its native media options, restoring YouTube stream playback.

This addresses the issues reported in #196, #166, and #214 where users experience black screens or broken streaming when using YouTube URLs.

Problem

When a user sets a YouTube URL in streaming mode, the following happens:

1. yt-dlp correctly extracts the direct video/audio stream URLs along with HTTP headers
2. However, yt_utils.py discards these headers and only returns the raw URLs
3. video_player.py passes the bare URLs to VLC without any HTTP headers
4. YouTube's CDN rejects the requests (missing User-Agent / Referer), resulting in a black screen

This issue has become more prominent as YouTube has tightened its request validation in recent months.

Changes

src/yt_utils.py

• Extract HTTP headers from yt-dlp info dict and individual format entries
• Ensure a default User-Agent is always present (YouTube blocks requests without one)
• Ensure a default Referer is set to the source URL (YouTube validates this)
• Propagate headers to all formats that don't have their own
• Return headers alongside URLs from get_best_audio() (now returns (url, headers)) and get_optimal_video() (now returns (url, width, height, headers))
• Add ValueError when no audio or video format is found, instead of failing silently

src/player/video_player.py

• media_new(): Pass User-Agent and Referer to VLC via native options (:http-user-agent, :http-referrer)
• add_audio_track(): Apply headers to the player's media for the audio slave track. Also fixes passing a URL string (not a Media object) to add_slave(), which previously caused a ctypes.ArgumentError
• MODE_STREAM block: Receive and forward headers from yt_utils, add :network-caching=3000 for smoother streaming, add info/debug logging for stream URLs and headers, wrap in try/except with detailed error logging

Backward compatibility

• Local video mode (MODE_VIDEO) is completely unaffected — http_headers defaults to None and all existing code paths remain unchanged
• Webpage mode (MODE_WEBPAGE) is untouched
• The return type changes in yt_utils.py only affect callers inside video_player.py's MODE_STREAM block, which is updated accordingly
• Works with any site supported by yt-dlp, not just YouTube

Testing

Tested manually on Kubuntu (KDE, Wayland via XWayland, Intel GPU):

• YouTube live streams: working (was black screen before)
• YouTube regular videos in stream mode: working (was black screen before)
• Local video files: still working, no regression
• Multi-monitor setup: working on both monitors

Note on yt-dlp version

Users running an older yt-dlp (< 2025.10) may still experience issues due to YouTube's SABR streaming protocol changes (see yt-dlp#12482). Updating yt-dlp to the latest version is recommended. This is independent of this PR but worth noting in documentation or release notes.