Video Sniffing

FlowPick automatically detects video content on webpages by monitoring browser network requests, supporting streaming protocols (HLS/DASH) and direct video files, with automatic decryption of AES-128 encrypted streams.

Detection Principles

FlowPick's video detection is based on the Chrome extension's webRequest API, intercepting requests at the browser network layer:

Detection Timing:

• After extension installation, need to refresh target page before detection can begin
• Streaming manifests typically load when video starts playing; recommend playing for 3-5 seconds before opening extension
• For dynamically loaded videos (e.g., loading when scrolling to specific position), need to trigger loading before detection

Supported Video Formats

Streaming Protocols

Direct Video Files

HLS (M3U8) Streams

HLS (HTTP Live Streaming) is a streaming protocol developed by Apple and currently the most widely used video transmission method on the web. Major platforms like Bilibili, Tencent Video, and Youku all use HLS.

Master Playlist vs Media Playlist

HLS manifests are divided into two levels:

FlowPick auto-identifies Master Playlists, parses out all quality options for you to select. After selecting quality, downloads corresponding Media Playlist to get fragment list.

Master Playlist (index.m3u8)
    │
    ├── 360p  → 360p.m3u8  →  segment-001.ts, segment-002.ts, ...
    ├── 720p  → 720p.m3u8  →  segment-001.ts, segment-002.ts, ...
    └── 1080p → 1080p.m3u8 →  segment-001.ts, segment-002.ts, ...

Quality Selection

Quality options parsed from Master Playlist are sorted by bitrate from high to low:

Fragment Download & Merging

HLS videos consist of large numbers of TS fragments (typically 2-10 seconds each). FlowPick's processing flow:

1. Parse Media Playlist to get all fragment URLs
2. Multi-threaded concurrent download of fragments (concurrency adjustable in settings)
3. After download completes, merge fragments into single file
4. If MP4 output selected, use FFmpeg WASM for remuxing

Encrypted Streams (AES-128)

Some HLS streams use AES-128 encryption to protect content. FlowPick supports automatic decryption:

• Detects #EXT-X-KEY:METHOD=AES-128,URI="..." tag
• Auto-downloads decryption key
• Uses Web Crypto API to decrypt each fragment in browser
• Decrypted fragments merge normally, output unencrypted file

DASH (MPD) Streams

DASH (Dynamic Adaptive Streaming over HTTP) is an international standard streaming protocol established by MPEG, widely used by platforms like YouTube and Netflix.

DASH Characteristics

Compared to HLS, DASH has these characteristics:

Separate Audio/Video Processing

A key characteristic of DASH is that video and audio are usually separated into independent tracks. FlowPick's processing flow:

1. Parse MPD manifest, identify video track and audio track
2. Download video fragments and audio fragments separately
3. Download initialization segments (init segment), containing codec configuration info
4. Use FFmpeg WASM to merge video and audio into single MP4 file

MPD Manifest
    │
    ├── AdaptationSet: Video (H.264, 1080p)
    │   ├── init segment (codec config)
    │   ├── segment-001.m4s
    │   ├── segment-002.m4s
    │   └── ...
    │
    └── AdaptationSet: Audio (AAC, 128kbps)
        ├── init segment (codec config)
        ├── segment-001.m4s
        ├── segment-002.m4s
        └── ...
                    ↓
            FFmpeg WASM Merge
                    ↓
              output.mp4

Encryption Support

Same as HLS, FlowPick supports AES-128 fragment-level encryption for DASH streams. DRM-protected streams (Widevine, PlayReady) cannot be handled.

Direct Video Files

For direct video files (MP4, WebM, MKV, etc.), detection and download process is simplest:

• Instant Detection: Video URL immediately detected when appears in network requests
• Direct Download: No fragment merging or format conversion needed, browser directly downloads original file
• Size Preview: If server returns Content-Length header, file size displayed

Direct video files typically appear in following scenarios:

• MP4 videos embedded directly in websites
• Short videos on social media
• Video assets on gallery websites
• Directly linked video files

Detection Differences: Extension vs Online Tool

Troubleshooting

Video Not Detected

Encrypted Stream Download Failed

Slow Download Speed

Merged Video Cannot Play

Related Documentation

• Usage Guide — Operation guide for video detection and download
• Audio Capture — Detection and download of audio files
• Image Download — Detection and batch download of image resources
• Format Conversion — Detailed technical explanation of TS/MP4 remuxing
• Download Engine Architecture — Fragment download, concurrency control, retry mechanism
• Online Tools — Feature comparison between extension and online tools
• Configuration Reference — Concurrent threads, output format and other settings
• Common Issues Troubleshooting — Diagnostic methods for download issues
• Known Limitations — DRM protection, Manifest V3 and other technical limitations
• Privacy & Security — Network monitoring and privacy protection notes