The to_dict() method was skipping signal_level when it was 0, so the
frontend never received the field and never rendered the monitor.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Shows RMS audio level bar and SSTV tone classification (leader/sync/noise)
via SSE during detecting mode, replacing the static "Listening..." state
with actionable signal feedback.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
When rtl_fm exits unexpectedly, read its stderr output to diagnose
the failure (no device, permission denied, etc.) and include the
error message in both the server log and the SSE progress event
sent to the browser.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Three bugs preventing the live SSTV pipeline from working:
1. Race condition: self._running was set AFTER starting the decode
thread, so the thread checked the flag, found it False, and exited
immediately without ever processing audio.
2. Ghost running state: when the decode thread exited (e.g. rtl_fm
died), self._running stayed True. The decoder reported as running
but was dead, and subsequent start() calls returned without doing
anything - permanently stuck until app restart.
3. VIS detection fragility: unclassifiable windows at tone transition
boundaries (mixed energy from two tones) caused the state machine
to reset from LEADER/BREAK states back to IDLE, dropping valid
VIS headers on real signals.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
slowrx is a GTK GUI app that doesn't support CLI usage, so the SSTV
decoder was silently failing. This replaces it with a pure Python
implementation using numpy and Pillow that supports Robot36/72,
Martin1/2, Scottie1/2, and PD120/180 modes via VIS header auto-detection.
Key implementation details:
- Generalized Goertzel (DTFT) for exact-frequency tone detection
- Vectorized batch Goertzel for real-time pixel decoding performance
- Overlapping analysis windows for short-window frequency estimation
- VIS header detection state machine with parity validation
- Per-line sync re-synchronization for drift tolerance
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
