Compressed audio (continuation of #36)

audioread/__init__.py

@@ -112,3 +112,18 @@ def audio_open(path):
 
     # All backends failed!
     raise NoBackendError()
+
+
+def decode(audio):
+    """Given a file-like object containing encoded audio data, create an
+    audio file object that produces its *raw* data.
+    """
+    # FFmpeg.
+    from . import ffdec
+    try:
+        return ffdec.FFmpegAudioFile(audio=audio)
+    except DecodeError:
+        pass
+
+    # All backends failed!
+    raise NoBackendError()

audioread/ffdec.py

@@ -53,27 +53,52 @@ class ReadTimeoutError(FFmpegError):
 
 
 class QueueReaderThread(threading.Thread):
-    """A thread that consumes data from a filehandle and sends the data
-    over a Queue.
+    """A thread that consumes data from a file-like object and sends the
+    data over a Queue.
     """
-    def __init__(self, fh, blocksize=1024, discard=False):
+    def __init__(self, file, blocksize=1024, discard=False):
         super(QueueReaderThread, self).__init__()
-        self.fh = fh
+        self.file = file
         self.blocksize = blocksize
         self.daemon = True
         self.discard = discard
         self.queue = None if discard else queue.Queue()
 
     def run(self):
         while True:
-            data = self.fh.read(self.blocksize)
+            data = self.file.read(self.blocksize)
             if not self.discard:
                 self.queue.put(data)
             if not data:
                 # Stream closed (EOF).
                 break
 
 
+class WriterThread(threading.Thread):
+    """A thread that reads data from one file-like object and writes it
+    to another, one block at a time.
+    """
+    def __init__(self, writefile, readfile=None, blocksize=1024):
+        """Create a thread that reads data from `readfile` and writes it
+        to `writefile`.
+        """
+        super(WriterThread, self).__init__()
+        self.writefile = writefile
+        self.readfile = readfile
+        self.blocksize = blocksize
+        self.daemon = True
+
+    def run(self):
+        while True:
+            data = self.readfile.read(self.blocksize)
+            if data:
+                self.writefile.write(data)
+            else:
+                # EOF.
+                break
+        self.writefile.close()
+
+
 def popen_multiple(commands, command_args, *args, **kwargs):
     """Like `subprocess.Popen`, but can try multiple commands in case
     some are not available.
@@ -100,7 +125,19 @@ def popen_multiple(commands, command_args, *args, **kwargs):
 
 class FFmpegAudioFile(object):
     """An audio file decoded by the ffmpeg command-line utility."""
-    def __init__(self, filename, block_size=4096):
+    def __init__(self, filename=None, audio=None, block_size=4096):
+        """Start decoding an audio file.
+
+        Provide either `filename` to read from the filesystem or
+        `audio`, a file-like object, to read from an open stream.
+        """
+        if filename:
+            self.from_file = True
+        elif audio:
+            self.from_file = False
+        else:
+            raise ValueError('one of `filename` or `audio` must be provided')
+
         # On Windows, we need to disable the subprocess's crash dialog
         # in case it dies. Passing SEM_NOGPFAULTERRORBOX to SetErrorMode
         # disables this behavior.
@@ -117,14 +154,17 @@ def __init__(self, filename, block_size=4096):
                 previous_error_mode | SEM_NOGPFAULTERRORBOX
             )
 
+        # Start the subprocess.
         try:
+            in_arg = filename if self.from_file else '-'
             self.devnull = open(os.devnull)
+            in_stream = self.devnull if self.from_file else subprocess.PIPE
             self.proc = popen_multiple(
                 COMMANDS,
-                ['-i', filename, '-f', 's16le', '-'],
+                ['-i', in_arg, '-f', 's16le', '-'],
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
-                stdin=self.devnull,
+                stdin=in_stream,
             )
 
         except OSError:
@@ -141,6 +181,14 @@ def __init__(self, filename, block_size=4096):
                 finally:
                     windows_error_mode_lock.release()
 
+        # If the input data comes from a stream, start a thread to write
+        # the compressed audio to the subprocess's standard input
+        # stream.
+        if not self.from_file:
+            self.stdin_writer = WriterThread(self.proc.stdin, audio,
+                                             block_size)
+            self.stdin_writer.start()
+
         # Start another thread to consume the standard output of the
         # process, which contains raw audio data.
         self.stdout_reader = QueueReaderThread(self.proc.stdout, block_size)

decode.py

@@ -21,21 +21,31 @@
 import contextlib
 
 
-def decode(filename):
-    filename = os.path.abspath(os.path.expanduser(filename))
-    if not os.path.exists(filename):
-        print("File not found.", file=sys.stderr)
-        sys.exit(1)
+def decode(filename=None):
+    """Decode audio from a file on disk or, if no file is specified,
+    from the standard input.
+    """
+    if filename:
+        filename = os.path.abspath(os.path.expanduser(filename))
+        if not os.path.exists(filename):
+            print("File not found.", file=sys.stderr)
+            sys.exit(1)
 
     try:
-        with audioread.audio_open(filename) as f:
+        if filename:
+            f = audioread.audio_open(filename)
+        else:
+            f = audioread.decode(sys.stdin)
+
+        with f:
             print('Input file: %i channels at %i Hz; %.1f seconds.' %
                   (f.channels, f.samplerate, f.duration),
                   file=sys.stderr)
             print('Backend:', str(type(f).__module__).split('.')[1],
                   file=sys.stderr)
 
-            with contextlib.closing(wave.open(filename + '.wav', 'w')) as of:
+            outname = filename or 'out'
+            with contextlib.closing(wave.open(outname + '.wav', 'w')) as of:
                 of.setnchannels(f.channels)
                 of.setframerate(f.samplerate)
                 of.setsampwidth(2)
@@ -49,4 +59,7 @@ def decode(filename):
 
 
 if __name__ == '__main__':
-    decode(sys.argv[1])
+    if sys.argv[1:]:
+        decode(sys.argv[1])
+    else:
+        decode()