feat: add LaughterFeatureExtractor

This adds functionality for getting laughter by using jrgillick's
laughter detection library

NB python expects all of the feature extractor's dependencies to be
available; perhaps in future we can do something even fancier like
activating another python env

[retroactive commit]

pipeline/feature_extractors.py

@@ -13,6 +13,7 @@ class FeatureExtractor(ABC):
 
     def teardown(self):
         pass
+
 class LaughterFeatureExtractor(FeatureExtractor):
     """Feature extractor for laughter detection.
 
@@ -28,3 +29,88 @@ class LaughterFeatureExtractor(FeatureExtractor):
 
     See: https://github.com/jrgillick/laughter-detection for the laughter-detection library
     """
+
+    def __init__(self, input_files=None, config=None):
+        """It is expected that input_files is a SourceMedia object"""
+        self.input_files = input_files
+        self.config = config
+        self.features = []
+
+    def _laughdetect(self, audio_file):
+        """Run laughter detection on the audio file"""
+        laugh_detector_dir = "/home/robert/mounts/980data/code/laughter-detection/"
+        laugh_detector_script = "segment_laughter.py"
+        # fake output for testing
+        # laugh_detector_path = "tests/fake_segment_laughter.py"
+        laugh_detector_cmd = ["python", f"{laugh_detector_dir}{laugh_detector_script}",
+                              f"--input_audio_file={audio_file}"]
+
+        # run command, capture output, ignore exit status
+        laugh_output = subprocess.run(laugh_detector_cmd,
+                                      stdout=subprocess.PIPE,
+                                      cwd=laugh_detector_dir).stdout.decode("utf-8")
+        # ↑ have to include cwd to keep laughter-detection imports happy
+        # also, it isn't happy if no output dir is specified but we get laughs so it's grand
+
+        # laughs are lines in stdout that start with "instance:", followed by a space and a 2-tuple of floats
+        # so jump to the 10th character and evaluate the rest of the line
+        return [literal_eval(instance[10:])
+                for instance in laugh_output.splitlines()
+                if instance.startswith("instance: ")]
+
+    def _adjust_features(self):
+        """Adjust features according to config
+
+        Generically, this ensures features conform to config - min/max feature length, etc.
+
+        In the context of LaughterFeatureExtractor, there is some secret sauce: things that
+        cause a laugh generally /precede/ the laugh, so we want more team before the detected start
+        than at the end. For example, for a minimum feature length of 15s, we might prepend 10 seconds,
+        and append 5 seconds (for example), or 12s and 3s. We may wish to do this pre/post adjustment
+        for all laughter features found, regardless of length.
+
+        TODO: figure out how we're going to handle length adjustments
+        TODO: config for length adjustments per design doc
+        TODO: play with numbers more to see what works best
+        """
+        PREPEND = 7.0
+        APPEND = 3.0
+
+        for feature in self.features:
+            # do the pre & post adjustment
+            feature.interval.move_start(-PREPEND, relative=True)
+            feature.interval.move_end(APPEND, relative=True)
+
+    def setup(self):
+        """Setup the laughter feature extractor -- validate input files & config
+
+        jrgillick's laughter-detection library can work with AV files directly
+
+        TODO: validate input files
+        TODO: handle config
+        """
+        logger.debug("LaughterFeatureExtractor setup")
+
+        # Validate input files
+        if not self.input_files:
+            raise ValueError("No input files provided")
+
+        # TODO: convert video to audio if needed
+
+    def run(self):
+        """Extract laughter features for each input file"""
+        if self.input_files:
+            for file in self.input_files:
+                laughs = self._laughdetect(file.path)
+                for laugh in laughs:
+                    start, end = laugh
+                    self.features.append(Feature(interval=Interval(start=start, end=end),
+                                                 source="laughter", path=file.path))
+                    # TODO: implement options eg minimum feature length
+
+        # adjust features
+        self._adjust_features()
+
+    def teardown(self):
+        pass
+