Add .audio + .video operators

examples/README.md

@@ -104,10 +104,10 @@ With additional filtering:
 ```python
 in1 = ffmpeg.input('in1.mp4')
 in2 = ffmpeg.input('in2.mp4')
-v1 = in1['v'].hflip()
-a1 = in1['a']
-v2 = in2['v'].filter('reverse').filter('hue', s=0)
-a2 = in2['a'].filter('areverse').filter('aphaser')
+v1 = in1.video.hflip()
+a1 = in1.audio
+v2 = in2.video.filter('reverse').filter('hue', s=0)
+a2 = in2.audio.filter('areverse').filter('aphaser')
 joined = ffmpeg.concat(v1, a1, v2, a2, v=1, a=1).node
 v3 = joined[0]
 a3 = joined[1].filter('volume', 0.8)

ffmpeg/nodes.py

@@ -53,8 +53,8 @@ def __getitem__(self, index):
             Process the audio and video portions of a stream independently::
 
                 input = ffmpeg.input('in.mp4')
-                audio = input[:'a'].filter("aecho", 0.8, 0.9, 1000, 0.3)
-                video = input[:'v'].hflip()
+                audio = input['a'].filter("aecho", 0.8, 0.9, 1000, 0.3)
+                video = input['v'].hflip()
                 out = ffmpeg.output(audio, video, 'out.mp4')
         """
         if self.selector is not None:
@@ -63,6 +63,56 @@ def __getitem__(self, index):
             raise TypeError("Expected string index (e.g. 'a'); got {!r}".format(index))
         return self.node.stream(label=self.label, selector=index)
 
+    @property
+    def audio(self):
+        """Select the audio-portion of a stream.
+
+        Some ffmpeg filters drop audio streams, and care must be taken
+        to preserve the audio in the final output.  The ``.audio`` and
+        ``.video`` operators can be used to reference the audio/video
+        portions of a stream so that they can be processed separately
+        and then re-combined later in the pipeline.  This dilemma is
+        intrinsic to ffmpeg, and ffmpeg-python tries to stay out of the
+        way while users may refer to the official ffmpeg documentation
+        as to why certain filters drop audio.
+
+        ``stream.audio`` is a shorthand for ``stream['a']``.
+
+        Example:
+            Process the audio and video portions of a stream independently::
+
+                input = ffmpeg.input('in.mp4')
+                audio = input.audio.filter("aecho", 0.8, 0.9, 1000, 0.3)
+                video = input.video.hflip()
+                out = ffmpeg.output(audio, video, 'out.mp4')
+        """
+        return self['a']
+
+    @property
+    def video(self):
+        """Select the video-portion of a stream.
+
+        Some ffmpeg filters drop audio streams, and care must be taken
+        to preserve the audio in the final output.  The ``.audio`` and
+        ``.video`` operators can be used to reference the audio/video
+        portions of a stream so that they can be processed separately
+        and then re-combined later in the pipeline.  This dilemma is
+        intrinsic to ffmpeg, and ffmpeg-python tries to stay out of the
+        way while users may refer to the official ffmpeg documentation
+        as to why certain filters drop audio.
+
+        ``stream.video`` is a shorthand for ``stream['v']``.
+
+        Example:
+            Process the audio and video portions of a stream independently::
+
+                input = ffmpeg.input('in.mp4')
+                audio = input.audio.filter("aecho", 0.8, 0.9, 1000, 0.3)
+                video = input.video.hflip()
+                out = ffmpeg.output(audio, video, 'out.mp4')
+        """
+        return self['v']
+
 
 def get_stream_map(stream_spec):
     if stream_spec is None:

ffmpeg/tests/test_ffmpeg.py

@@ -175,10 +175,15 @@ def test_combined_output():
     ]
 
 
-def test_filter_with_selector():
+@pytest.mark.parametrize('use_shorthand', [True, False])
+def test_filter_with_selector(use_shorthand):
     i = ffmpeg.input(TEST_INPUT_FILE1)
-    v1 = i['v'].hflip()
-    a1 = i['a'].filter('aecho', 0.8, 0.9, 1000, 0.3)
+    if use_shorthand:
+        v1 = i.video.hflip()
+        a1 = i.audio.filter('aecho', 0.8, 0.9, 1000, 0.3)
+    else:
+        v1 = i['v'].hflip()
+        a1 = i['a'].filter('aecho', 0.8, 0.9, 1000, 0.3)
     out = ffmpeg.output(a1, v1, TEST_OUTPUT_FILE1)
     assert out.get_args() == [
         '-i', TEST_INPUT_FILE1,
@@ -273,7 +278,7 @@ def test_filter_concat__audio_only():
 def test_filter_concat__audio_video():
     in1 = ffmpeg.input('in1.mp4')
     in2 = ffmpeg.input('in2.mp4')
-    joined = ffmpeg.concat(in1['v'], in1['a'], in2.hflip(), in2['a'], v=1, a=1).node
+    joined = ffmpeg.concat(in1.video, in1.audio, in2.hflip(), in2['a'], v=1, a=1).node
     args = (
         ffmpeg
         .output(joined[0], joined[1], 'out.mp4')
@@ -298,7 +303,7 @@ def test_filter_concat__wrong_stream_count():
     in1 = ffmpeg.input('in1.mp4')
     in2 = ffmpeg.input('in2.mp4')
     with pytest.raises(ValueError) as excinfo:
-        ffmpeg.concat(in1['v'], in1['a'], in2.hflip(), v=1, a=1).node
+        ffmpeg.concat(in1.video, in1.audio, in2.hflip(), v=1, a=1).node
     assert str(excinfo.value) == \
         'Expected concat input streams to have length multiple of 2 (v=1, a=1); got 3'
 

setup.py

@@ -67,6 +67,13 @@
     keywords=keywords,
     long_description=long_description,
     install_requires=['future'],
+    extras_require={
+        'dev': [
+            'future',
+            'pytest',
+            'pytest-mock',
+        ],
+    },
     classifiers=[
         'Intended Audience :: Developers',
         'License :: OSI Approved :: Apache Software License',