docs: Add summary of Jetson HLS fix

Adds a markdown file (`JETSON_HLS_FIX_SUMMARY.md`) documenting the technical details of the HLS recording fix implemented for Jetson Nano systems.

The document explains:
- The problem encountered with HLS recording on Jetson Nano using GStreamer 1.23.0.
- The root cause related to GStreamer segment events, race conditions, and hardware differences.
- The implemented solution steps (explicit mux control, segment event injection, delayed element start).
- Testing steps and expected results.
- Key code changes and architecture notes related to the fix.

[auto-enhanced]

Author: Steve

JETSON_HLS_FIX_SUMMARY.md

@@ -0,0 +1,51 @@
+# Jetson Nano HLS Recording Fix Summary
+
+## Problem
+On Jetson Nano 2GB running GStreamer 1.23.0 (development version), HLS recording was showing "Got data flow before segment event" warnings from mpegtsmux. This didn't occur on x86/WSL systems.
+
+## Root Cause
+1. **GStreamer 1.23.0** has stricter segment event checking
+2. **Jetson Nano 2GB** slower processing exposes race conditions
+3. Dynamic pad linking from webrtcbin causes segment events to arrive after data
+
+## Solution Implemented
+
+### 1. Explicit mpegtsmux Control
+- Create our own mpegtsmux element (except for splitmuxsink which manages its own)
+- Configure with proper HLS alignment settings
+- Direct control over element state transitions
+
+### 2. Segment Event Injection
+- Add pad probes on video/audio queues before mux
+- Inject segment events before first buffer reaches mux
+- Ensures proper event ordering
+
+### 3. Delayed Element Start
+- 100ms delay after pad connections before starting mux/sink
+- Allows segment events to propagate on slower systems
+- Prevents race condition
+
+### 4. Dual Mode Support
+- **splitmuxsink**: Uses internal mux, connects directly
+- **manual mode**: Uses explicit mux for future m3u8 support
+
+## Testing
+Run on Jetson Nano:
+```bash
+python3 publish.py --record-room --hls --room TestRoom --webserver 8087
+```
+
+Expected results:
+- No segment event warnings
+- HLS files created successfully
+- Clean state transitions logged
+
+## Key Code Changes
+1. `setup_hls_muxer()`: Creates explicit mpegtsmux or uses internal
+2. Video/audio pad connections: Route through mux with segment injection
+3. `check_hls_streams_ready()`: Delayed start with proper state management
+
+## Architecture Notes
+- GStreamer dev versions (1.23.x) have stricter checks than stable
+- ARM scheduling differences expose latent timing bugs
+- Explicit pipeline control prevents race conditions