replaygain: ffmpeg: check version

Check if the libavfilter library supports replaygain calculation. Before version
6.67.100 that did require the `--enable-libebur128` compile-time-option, after
that the ebur128 library is included in libavfilter itself.

Thus we require either a recent enough libavfilter version or the
`--enable-libebur128` option.

beetsplug/replaygain.py

@@ -318,13 +318,28 @@ def __init__(self, config, log):
         self._ffmpeg_path = "ffmpeg"
 
         # check that ffmpeg is installed
-        # TODO: check if ffmpeg version is sufficient
         try:
-            call([self._ffmpeg_path, "-version"])
+            ffmpeg_version_out = call([self._ffmpeg_path, "-version"])
         except OSError:
             raise FatalReplayGainError(
                 u"could not find ffmpeg at {0}".format(self._ffmpeg_path)
             )
+        incompatible_ffmpeg = True
+        for line in ffmpeg_version_out.stdout.splitlines():
+            if line.startswith(b"configuration:"):
+                if b"--enable-libebur128" in line:
+                    incompatible_ffmpeg = False
+            if line.startswith(b"libavfilter"):
+                version = line.split(b" ", 1)[1].split(b"/", 1)[0].split(b".")
+                version = tuple(map(int, version))
+                if version >= (6, 67, 100):
+                    incompatible_ffmpeg = False
+        if incompatible_ffmpeg:
+            raise FatalReplayGainError(
+                u"Installed FFmpeg version does not support ReplayGain."
+                u"calculation. Either libavfilter version 6.67.100 or above or"
+                u"the --enable-libebur128 configuration option is required."
+            )
 
         # check that peak_method is valid
         valid_peak_method = ("true", "sample")