refactor+fix: extract calls to run, fix args

Extract method _run_no_output for two calls to ffmpeg

Fix feature.path → feature.source.path after Feature API change

pipeline/video_producers.py

@@ -29,6 +29,13 @@ class FfmpegVideoProducer(VideoProducer):
     """Produce videos using ffmpeg"""
     # TODO: consider output filename options
 
+    def _run_no_output(self, cmd: list, cwd:str=".") -> None:
+        """Run a command and return the output as a string
+
+        Defined to be mocked out in tests via unittest.mock.patch
+        """
+        subprocess.run(cmd, stdout=None, stderr=None, cwd=cwd)
+
     def __init__(self, features):
         if not features:
             raise ValueError("No features provided")
@@ -50,9 +57,10 @@ class FfmpegVideoProducer(VideoProducer):
         # TODO: adjustable encoding options
         seek = ["-ss", str(feature.interval.start)]
         duration = ["-t", str(feature.interval.duration)]
-        ffmpeg_args = ffmpeg_prefix + seek + ["-i"] + [feature.path] + duration + ffmpeg_suffix + [output_filepath]
+        ffmpeg_args = ffmpeg_prefix + seek + ["-i"] + [feature.source.path] +\
+            duration + ffmpeg_suffix + [output_filepath]
         logging.info(f"ffmpeg_args: {ffmpeg_args}")
-        subprocess.run(ffmpeg_args, stdout=None, stderr=None)
+        self._run_no_output(ffmpeg_args)
 
     def _ffmpeg_concat_clips(self, clips=None, output_filepath=None):
         """use ffmpeg to concatenate clips into a single video"""
@@ -78,7 +86,7 @@ class FfmpegVideoProducer(VideoProducer):
 
         ffmpeg_args = ffmpeg_prefix + [join_file.name] + ["-c", "copy", output_filepath]
         logging.info(f"ffmpeg_args: {ffmpeg_args}")
-        subprocess.run(ffmpeg_args, stdout=None, stderr=None)
+        self._run_no_output(ffmpeg_args)
         join_file.close()
 
     def produce(self):