feat(analyzer): analyze cuepoint using ffmpeg

- store cue(in|out) as strings
- reraise when executable was not found

BREAKING CHANGE: The analyzer requires 'ffmpeg'. The 'silan' system dependency can be removed.

analyzer/libretime_analyzer/ffmpeg.py

@@ -1,6 +1,7 @@
 import re
+from math import inf
 from pathlib import Path
-from typing import Optional
+from typing import List, Optional, Tuple
 
 from .utils import run_
 
@@ -54,3 +55,56 @@ def compute_replaygain(filepath: Path) -> Optional[float]:
 
     if track_gain_match:
         return float(track_gain_match.group(1))
+
+
+_SILENCE_DETECT_RE = re.compile(
+    r"\[silencedetect.*\] silence_(start|end): (-?\d+(?:\.\d+)?)(?: \| silence_duration: (\d+(?:\.\d+)?))?"
+)
+
+
+def compute_silences(filepath: Path) -> List[Tuple[float, float]]:
+    """
+    Compute silence will analyse the given audio file and return a list of silences.
+    """
+    cmd = _ffmpeg(
+        *("-i", filepath),
+        "-vn",
+        *("-filter", "highpass=frequency=1000"),
+        *("-filter", "silencedetect=noise=0.15:duration=1"),
+    )
+
+    starts, ends = [], []
+    for line in cmd.stderr.splitlines():
+        match = _SILENCE_DETECT_RE.search(line)
+        if match is None:
+            continue
+
+        kind = match.group(1)
+        if kind == "start":
+            start = float(match.group(2))
+            start = max(start, 0.0)
+            starts.append(start)
+        elif kind == "end":
+            end = float(match.group(2))
+            ends.append(end)
+
+    # ffmpeg v3 (bionic) does not warn about silence end when the track ends.
+    # Set the last silence ending to infinity, and clamp it to the track duration before
+    # using this value.
+    if len(starts) - 1 == len(ends):
+        ends.append(inf)
+
+    return list(zip(starts, ends))
+
+
+def probe_duration(filepath: Path) -> float:
+    """
+    Probe duration will probe the given audio file and return the duration.
+    """
+    cmd = _ffprobe(
+        *("-i", filepath),
+        *("-show_entries", "format=duration"),
+        *("-v", "quiet"),
+        *("-of", "csv=p=0"),
+    )
+    return float(cmd.stdout.strip("\n"))