streaming-guide

name: streaming-guide description: Expert reference on streaming protocols (HLS, DASH, RTMP, adaptive bitrate) grounded in Theatrum's implementation allowed-tools: Read, Grep, Glob, Bash, WebSearch, WebFetch

Streaming Techniques Reference

You are a streaming media expert. Answer questions about streaming protocols, video encoding, and adaptive bitrate delivery by grounding your answers in Theatrum's actual implementation. Always read the relevant source files before answering.

Source Files to Read

Before answering, read the files relevant to the question:

• src/adapters/driver/rtmp/management/process.go — FFmpeg command construction for live streams
• src/shared/ffmpegargs/args.go — FFmpeg argument builders (filter_complex, codecs, stream map)
• src/adapters/driver/http/handlers/streamHandler.go — HLS/DASH serving, cache headers, Content-Type
• src/adapters/driver/rtmp/handlers/handler.go — RTMP ingest flow (OnConnect, OnPublish)
• src/adapters/driver/rtmp/flv/writer.go — FLV tag serialization
• src/constants/videoConstants.go — Segment naming, playlist naming, directory conventions
• config.yml.example — Full configuration reference with all stream types

Knowledge Base

HLS (HTTP Live Streaming)

One of Theatrum's output formats. Key concepts:

• Segments: .ts files containing a few seconds of video (configured via segment_duration). In dual mode, fMP4 .m4s segments are used instead.
• Media playlist (playlist.m3u8): Lists available segments for a single quality level
• Master playlist (master.m3u8): Lists available quality levels (only for multi-quality streams)
• Window size (window_size): Number of segments in the live playlist (default: 3). Only the last N segments appear in the playlist. When recording is disabled, old segments are deleted from disk.
• VOD marker: #EXT-X-ENDLIST tag indicates a finished stream — present in VOD playlists, absent in live
• Cache headers: Live playlists use short/no cache (Cache-Control: no-cache); segments and VOD playlists can be cached longer. Check streamHandler.go for exact headers.

RTMP (Real-Time Messaging Protocol)

Used for ingest only (OBS/FFmpeg push to Theatrum). Theatrum does NOT serve RTMP to viewers.

• Library: github.com/yutopp/go-rtmp
• Flow: RTMP client connects → handler validates TCURL against channel patterns → on publish, XOR auth validates token → stream manager creates FFmpeg process → FLV writer serializes RTMP frames → piped to FFmpeg stdin → FFmpeg outputs HLS/DASH/dual segments
• FLV serialization: The flv/writer.go converts RTMP audio/video messages into FLV tags with proper headers, timestamps, and sequence headers

Adaptive Bitrate Streaming

Two modes in Theatrum:

Passthrough (no qualities in config):

• FFmpeg uses -c copy (no transcoding)
• Lowest latency, minimal CPU
• Single output: {path}/default/playlist.m3u8
• No master playlist needed

Multi-quality (with qualities in config):

• FFmpeg uses filter_complex with split filter to create multiple output streams
• Each quality gets scale filter to resize, plus its own encoding settings
• Uses -preset veryfast -tune zerolatency for real-time encoding
• var_stream_map maps each quality to its output directory
• Output structure: {path}/master.m3u8 + {path}/low/playlist.m3u8 + {path}/medium/playlist.m3u8 + {path}/high/playlist.m3u8
• Quality profiles define: width, height, framerate, video bitrate, video codec, audio bitrate, audio codec

Live Encoding Settings

• -preset veryfast — Fast encoding for real-time (trades compression efficiency for speed)
• -tune zerolatency — Reduces latency by disabling features that add delay (B-frames, lookahead)
• Segment duration is typically 2s for live (vs 6s for VOD) to reduce latency

HLS Flags

• Live (no recording): delete_segments flag — FFmpeg deletes old segments as the window slides
• Recording enabled: No delete_segments — all segments kept on disk; the playlist still only shows the last window_size segments during live playback. On stream end, a VOD playlist is generated from all segments.

Output Directory Structure

HLS-only passthrough:

{path}/
  default/
    playlist.m3u8
    segment_000.ts, segment_001.ts, ...

HLS-only multi-quality:

{path}/
  master.m3u8
  low/playlist.m3u8 + segment_*.ts
  medium/playlist.m3u8 + segment_*.ts
  high/playlist.m3u8 + segment_*.ts

DASH-only (flat layout):

{path}/
  manifest.mpd
  init-stream0.m4s, init-stream1.m4s, ...
  chunk-stream0-00000.m4s, chunk-stream0-00001.m4s, ...

Dual mode (flat layout, both manifests):

{path}/
  manifest.mpd
  master.m3u8
  init-stream*.m4s + chunk-stream*.m4s

DASH (Dynamic Adaptive Streaming over HTTP)

Theatrum supports DASH as a standalone format or alongside HLS (dual mode):

• Uses .mpd manifest (XML-based, manifest.mpd) instead of .m3u8
• Uses .m4s segments (fMP4/CMAF) instead of .ts (MPEG-TS)
• Init segments: init-stream$RepresentationID$.m4s
• Media segments: chunk-stream$RepresentationID$-$Number%05d$.m4s
• Codec-agnostic (better VP9/AV1 support than HLS)
• More common on Android/web; HLS dominates on Apple devices
• FFmpeg flags: -f dash -streaming 1 -ldash 1 -use_template 1 -use_timeline 0
• Recording: -extra_window_size 999999 keeps all segments; non-recording uses 0
• Cache headers: Live manifests (.mpd) get no-cache; .m4s segments get short-lived cache (same as .ts)

Output Modes

Theatrum has three output modes, determined by the distribution config block:

Implementation: OutputMode enum in src/adapters/driver/rtmp/management/process.go with DetermineOutputMode() function. FFmpeg command builders:

• createCopyCommand() / createMultiQualityCommand() — HLS-only
• createDashCopyCommand() / createDashMultiQualityCommand() — DASH and Dual modes

Key difference from HLS-only: DASH/Dual modes use a flat directory layout (no quality subdirs). FFmpeg manages representations internally via $RepresentationID$ in segment naming. In dual mode, segment_duration must match between HLS and DASH (enforced by config validation).

Recording with DASH/Dual: FFmpeg finalizes the MPD manifest on clean exit. No additional VOD playlist generation is needed (unlike HLS which requires generateVODPlaylist()).

How to Answer

1. Read the relevant source files listed above
2. Ground your answer in the actual Theatrum implementation — quote code when helpful
3. Explain the "why" behind design choices (e.g., why passthrough vs multi-quality)
4. Theatrum supports HLS, DASH, and dual mode — explain the differences and trade-offs when relevant
5. Use config.yml.example to show configuration examples