Hey there! Let’s walk through your music player needs and cover both off-the-shelf tools and custom development paths that’ll work perfectly for your party-friendly setup.

Core Requirements Breakdown & Solutions #

• Dual-source playback (local files + Spotify)
  For ready-to-use options, players like MusicBee or Clementine natively support local file libraries and can connect to Spotify via its official API. If you’re open to building something custom, you can pair libraries like librespot (for Spotify streaming) with audio processing tools such as ffmpeg or gstreamer to handle local file decoding seamlessly.
• Cross-fade between tracks
  This relies on gradual audio volume blending during transitions. Most modern players let you enable cross-fade in their settings (look for options labeled "crossfade duration"). If building from scratch, you can implement this by slowly lowering the current track’s volume while ramping up the next one over a set timeframe—libraries like pydub (Python) or PortAudio make this straightforward, matching the smooth behavior of the official Spotify app.
• Queue-friendly behavior (no accidental clears)
  This is make-or-break for party settings! First, check your player’s settings: many let you change the default action of clicking a song from "replace queue and play immediately" to "add to queue". For custom builds, design your queue as a persistent list data structure—whenever a user selects a song, append it to the end instead of overwriting the queue. Adding visual feedback (like a visible queue list) will also help everyone track upcoming tracks.

Bonus Features: YouTube Playback with Dual-Screen Video #

• YouTube audio + video playback
  Tools like MPV can handle YouTube streams natively (powered by yt-dlp under the hood) and let you separate audio and video output. To display the video on a second screen, you can pass command-line arguments like --fs-screen=2 to force the video window to fullscreen on your secondary display, while keeping the main player controls on your primary screen. For a custom GUI, you could use frameworks like Qt or Electron to build a standalone video window, pulling stream data via yt-dlp and rendering it independently of the audio player.

Quick Recommendation for Non-Developers #

If you don’t want to build something custom, try pairing Spotify Desktop with its local file integration—you can add local files to your Spotify library, enable cross-fade in settings, and set "Add to Queue" as your default action (use right-click or hold shift to add songs if needed). For YouTube, combine this with MPV to handle streaming and dual-screen video setup effortlessly.

备注：内容来源于stack exchange，提问作者lumbric