DAB+ audio: WAV default for all sample rates (24/32/48 kHz), stereo input fix

- Default: dablin -w so ffmpeg reads rate and channels from WAV header;
  all DAB+ services (24/32/48 kHz, mono/stereo) play at correct speed.
- Fallback: OPENWEBRX_DAB_USE_WAV=0 uses PCM path with
  OPENWEBRX_DAB_INPUT_RATE (24000|32000|48000).
- Fix: treat dablin output as stereo (-ac 2); mono caused consistently
  slow playback.
- Optional OPENWEBRX_DAB_CAPTURE_RAW=1 for raw PCM capture (PCM path).
- README-FORK.md: document env vars and behaviour.

README-FORK.md

@@ -0,0 +1,30 @@
+# dom-robinson/openwebrx fork – DAB+ sample rate fix
+
+This is a clone of [dom-robinson/openwebrx](https://github.com/dom-robinson/openwebrx) with branch **feature/dab-audio-fix** containing improvements over upstream [jketterl/openwebrx PR #419](https://github.com/jketterl/openwebrx/pull/419): **Fix DAB+ audio sample rate issues using ffmpeg resampling**.
+
+## What’s in this branch
+
+- **owrx/dab/dablin.py** – DAB+ audio fix with **automatic handling of all sample rates (24/32/48 kHz)** and mono/stereo:
+  - **Default (WAV path):** `dablin -w` so ffmpeg reads sample rate and channel count from the WAV header; resample to 48 kHz stereo. All DAB+ services play at correct speed without configuration.
+  - **Fallback (PCM path):** Set `OPENWEBRX_DAB_USE_WAV=0` and optionally `OPENWEBRX_DAB_INPUT_RATE=24000|32000|48000` if WAV causes issues. Optional `OPENWEBRX_DAB_CAPTURE_RAW=1` tees raw PCM to `/tmp/dablin_capture.raw` for analysis.
+  - **Critical fix:** Treat dablin output as **stereo** (`-ac 2`) when using PCM; using mono caused consistently slow playback.
+- **docker/scripts/install-dependencies.sh** – Add `sox` to static packages.
+- **Dockerfile.hotfix** – Optional image that builds dablin from source and applies the dablin.py patch.
+
+## Environment variables (optional)
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `OPENWEBRX_DAB_USE_WAV` | `1` | Use dablin WAV output so rate/channels are automatic. Set `0` to use PCM path with fixed rate. |
+| `OPENWEBRX_DAB_INPUT_RATE` | `32000` | Only when `OPENWEBRX_DAB_USE_WAV=0`: input rate 24000, 32000, or 48000. |
+| `OPENWEBRX_DAB_CAPTURE_RAW` | unset | Set to `1` to tee raw PCM to `/tmp/dablin_capture.raw` (PCM path only, for analysis). |
+
+## Push this branch to the fork
+
+From this directory, with GitHub auth set up:
+
+```bash
+git push -u origin feature/dab-audio-fix
+```
+
+After pushing, the fork on GitHub will list the branch and you can open or update a PR to jketterl/openwebrx, or build images from it.

owrx/dab/dablin.py

@@ -1,3 +1,4 @@
+import os
 from pycsdr.modules import ExecModule
 from pycsdr.types import Format
 
@@ -12,8 +13,30 @@ class DablinModule(ExecModule):
         )
 
     def _buildArgs(self):
-        # Use -w so dablin outputs WAV (with correct sample rate in header); ffmpeg then resamples to 48k
-        return ["bash", "-c", "dablin -w -s {:#06x} | mbuffer -q -m 1M | ffmpeg -v error -i pipe:0 -f f32le -ar 48000 -ac 1 pipe:1".format(self.serviceId)]
+        # Two paths:
+        # 1) WAV (default): dablin -w so ffmpeg reads rate and channels from header → 24/32/48 kHz and mono/stereo all work.
+        # 2) PCM: set OPENWEBRX_DAB_USE_WAV=0 and OPENWEBRX_DAB_INPUT_RATE=24000|32000|48000 if WAV causes issues.
+        # Optional: OPENWEBRX_DAB_CAPTURE_RAW=1 tees raw PCM to /tmp/dablin_capture.raw (PCM path only).
+        use_wav = os.environ.get("OPENWEBRX_DAB_USE_WAV", "1") != "0"
+        if use_wav:
+            dab_cmd = (
+                "dablin -w -s {:#06x} | mbuffer -q -m 4M | "
+                "ffmpeg -v error -probesize 4096 -analyzeduration 0 -f wav -i pipe:0 "
+                "-af aresample=48000 -f f32le -ar 48000 -ac 2 pipe:1"
+            ).format(self.serviceId)
+        else:
+            rate = int(os.environ.get("OPENWEBRX_DAB_INPUT_RATE", "32000"))
+            if rate not in (24000, 32000, 48000):
+                rate = 32000
+            dab_cmd = "echo {} > /tmp/dablin_rate.txt 2>/dev/null; dablin -p -s {:#06x}".format(rate, self.serviceId)
+            if os.environ.get("OPENWEBRX_DAB_CAPTURE_RAW"):
+                dab_cmd += " | tee >(dd of=/tmp/dablin_capture.raw bs=1M count=5 2>/dev/null)"
+            dab_cmd += (
+                " | mbuffer -q -m 4M | "
+                "ffmpeg -v error -f s16le -ar {} -ac 2 -i pipe:0 "
+                "-af aresample=48000 -f f32le -ar 48000 -ac 2 pipe:1"
+            ).format(rate)
+        return ["bash", "-c", dab_cmd]
 
     def setDabServiceId(self, serviceId: int) -> None:
         self.serviceId = serviceId