Video download support

[filthyrake]

Summary

Allow users to download videos in original or transcoded formats.

Current State

Videos can only be streamed via HLS. There's no way to download the original source file or a specific quality variant.

Proposed Features

• Download Original: Download the source file as uploaded
• Download Transcoded: Download a specific quality (e.g., 1080p MP4)
• Optional: Generate downloadable MP4 from HLS segments

API Endpoints

GET /api/videos/{slug}/download/original
GET /api/videos/{slug}/download/{quality}  # e.g., 1080p

Configuration Options

• VLOG_DOWNLOADS_ENABLED: Enable/disable download feature
• VLOG_DOWNLOADS_REQUIRE_AUTH: Require authentication for downloads
• VLOG_DOWNLOADS_RATE_LIMIT: Rate limit download requests
• VLOG_DOWNLOADS_ORIGINAL_ONLY: Only allow original downloads (no transcoded)

UI Changes

• Download button on video page
• Quality selector dropdown for transcoded downloads
• Download progress indication (for large files)

Implementation Considerations

• Streaming response for large files (don't load into memory)
• Consider generating MP4 from HLS segments on-demand or pre-generating
• Track download analytics (similar to view tracking)
• Consider bandwidth implications for self-hosted deployments

Security

• Optional authentication requirement
• Rate limiting to prevent abuse
• Consider signed URLs with expiration

Priority

High - common feature request for video platforms