python-audioread 0.3-1 / usr / share / pyshared / audioread / gstdec.py

# This file is part of audioread.
# Copyright 2011, Adrian Sampson.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

"""Use Gstreamer to decode audio files.

To read an audio file, pass it to the constructor for GstAudioFile()
and then iterate over the contents:

    >>> f = GstAudioFile('something.mp3')
    >>> try:
    >>>     for block in f:
    >>>         ...
    >>> finally:
    >>>     f.close()

Note that there are a few complications caused by Gstreamer's
asynchronous architecture. This module spawns its own Gobject main-
loop thread; I'm not sure how that will interact with other main
loops if your program has them. Also, in order to stop the thread
and terminate your program normally, you need to call the close()
method on every GstAudioFile you create. Conveniently, the file can be
used as a context manager to make this simpler:

    >>> with GstAudioFile('something.mp3') as f:
    >>>     for block in f:
    >>>         ...

Iterating a GstAudioFile yields strings containing short integer PCM
data. You can also read the sample rate and channel count from the
file:

    >>> with GstAudioFile('something.mp3') as f:
    >>>     print f.samplerate
    >>>     print f.channels
    >>>     print f.duration
"""
from __future__ import with_statement

import gst
import sys
import gobject
import threading
import os
import urllib
import Queue

QUEUE_SIZE = 10
BUFFER_SIZE = 10
SENTINEL = '__GSTDEC_SENTINEL__'


# Exceptions.

class GStreamerError(Exception):
    pass

class UnknownTypeError(GStreamerError):
    """Raised when Gstreamer can't decode the given file type."""
    def __init__(self, streaminfo):
        super(UnknownTypeError, self).__init__(
            "can't decode stream: " + streaminfo
        )
        self.streaminfo = streaminfo

class FileReadError(GStreamerError):
    """Raised when the file can't be read at all."""
    pass

class NoStreamError(GStreamerError):
    """Raised when the file was read successfully but no audio streams
    were found.
    """
    def __init__(self):
        super(NoStreamError, self).__init__('no audio streams found')


# Managing the Gobject main loop thread.

_shared_loop_thread = None
_loop_thread_lock = threading.RLock()
gobject.threads_init()
def get_loop_thread():
    """Get the shared main-loop thread.
    """
    global _shared_loop_thread
    with _loop_thread_lock:
        if not _shared_loop_thread:
            # Start a new thread.
            _shared_loop_thread = MainLoopThread()
            _shared_loop_thread.start()
        return _shared_loop_thread
class MainLoopThread(threading.Thread):
    """A daemon thread encapsulating a Gobject main loop.
    """
    def __init__(self):   
        super(MainLoopThread, self).__init__()             
        self.loop = gobject.MainLoop()
        self.running = False
        self.daemon = True
        
    def run(self):    
        self.running = True
        self.loop.run()


# The decoder.

class GstAudioFile(object):
    """Reads raw audio data from any audio file that Gstreamer
    knows how to decode.
    
        >>> with GstAudioFile('something.mp3') as f:
        >>>     print f.samplerate
        >>>     print f.channels
        >>>     print f.duration
        >>>     for block in f:
        >>>         do_something(block)
    
    Iterating the object yields blocks of 16-bit PCM data. Three
    pieces of stream information are also available: samplerate (in Hz),
    number of channels, and duration (in seconds).
    
    It's very important that the client call close() when it's done
    with the object. Otherwise, the program is likely to hang on exit.
    Alternatively, of course, one can just use the file as a context
    manager, as shown above.
    """
    def __init__(self, path):
        self.running = False
        self.finished = False
        
        # Set up the Gstreamer pipeline.
        self.pipeline = gst.Pipeline()
        self.dec = gst.element_factory_make("uridecodebin")
        self.conv = gst.element_factory_make("audioconvert")
        self.sink = gst.element_factory_make('appsink')
        
        # Register for bus signals.
        bus = self.pipeline.get_bus()
        bus.add_signal_watch()
        bus.connect("message::eos", self._message)
        bus.connect("message::error", self._message)
        
        # Configure the input.
        uri = 'file://' + urllib.quote(path)
        self.dec.set_property("uri", uri)
        # The callback to connect the input.
        self.dec.connect("pad-added", self._pad_added)
        self.dec.connect("no-more-pads", self._no_more_pads)
        # And a callback if decoding failes.
        self.dec.connect("unknown-type", self._unkown_type)
        
        # Configure the output.
        # We want short integer data.
        self.sink.set_property('caps',
            gst.Caps('audio/x-raw-int, width=16, depth=16, signed=true')
        )
        # TODO set endianness?
        # Set up the characteristics of the output. We don't want to
        # drop any data (nothing is real-time here); we should bound
        # the memory usage of the internal queue; and, most
        # importantly, setting "sync" to False disables the default
        # behavior in which you consume buffers in real time. This way,
        # we get data as soon as it's decoded.
        self.sink.set_property('drop', False)
        self.sink.set_property('max-buffers', BUFFER_SIZE)
        self.sink.set_property('sync', False)
        # The callback to receive decoded data.
        self.sink.set_property('emit-signals', True)
        self.sink.connect("new-buffer", self._new_buffer)
        
        # We'll need to know when the stream becomes ready and we get
        # its attributes. This semaphore will become available when the
        # caps are received. That way, when __init__() returns, the file
        # (and its attributes) will be ready for reading.
        self.ready_sem = threading.Semaphore(0)
        self.caps_handler = self.sink.get_pad("sink").connect(
            "notify::caps", self._notify_caps
        )
        
        # Link up everything but the decoder (which must be linked only
        # when it becomes ready).
        self.pipeline.add(self.dec, self.conv, self.sink)
        self.conv.link(self.sink)
        
        # Set up the queue for data and run the main thread.
        self.queue = Queue.Queue(QUEUE_SIZE)
        self.thread = get_loop_thread()
        
        # This wil get filled with an exception if opening fails.
        self.read_exc = None
        
        # Return as soon as the stream is ready!
        self.pipeline.set_state(gst.STATE_PLAYING)
        self.ready_sem.acquire()
        if self.read_exc:
            # An error occurred before the stream became ready.
            self.close(True)
            raise self.read_exc
        self.running = True
    
    
    # Gstreamer callbacks.
    
    def _notify_caps(self, pad, args):
        # The sink has started to receive data, so the stream is ready.
        # This also is our opportunity to read information about the
        # stream.
        info = pad.get_negotiated_caps()[0]
        
        # Stream attributes.
        self.channels = info['channels']
        self.samplerate = info['rate']
        
        # Query duration.
        q = gst.query_new_duration(gst.FORMAT_TIME)
        if pad.get_peer().query(q):
            # Success.
            format, length = q.parse_duration()
            if format == gst.FORMAT_TIME:
                self.duration = float(length) / 1000000000
            else:
                # Not sure what happened.
                self.duration = None
        else:
            # Failure.
            self.duration = None
        
        # Allow constructor to complete.
        self.ready_sem.release()
    
    _got_a_pad = False
    def _pad_added(self, element, pad):
        # Decoded data is ready. Connect up the decoder, finally.
        name = pad.get_caps()[0].get_name()
        if name.startswith('audio/x-raw-'):
            nextpad = self.conv.get_pad('sink')
            if not nextpad.is_linked():
                self._got_a_pad = True
                pad.link(nextpad)
    
    def _no_more_pads(self, element):
        # Sent when the pads are done adding (i.e., there are no more
        # streams in the file). If we haven't gotten at least one
        # decodable stream, raise an exception.
        if not self.running and not self._got_a_pad:
            self.read_exc = NoStreamError()
            self.ready_sem.release()
    
    def _new_buffer(self, sink):
        if self.running:
            # New data is available from the pipeline! Dump it into our
            # queue (or possibly block if we're full).
            buf = sink.emit('pull-buffer')
            self.queue.put(str(buf))
    
    def _unkown_type(self, uridecodebin, decodebin, caps):
        # This is called *before* the stream becomes ready when the
        # file can't be read.
        streaminfo = caps.to_string()
        if not streaminfo.startswith('audio/'):
            # Ignore non-audio (e.g., video) decode errors.
            return
        self.read_exc = UnknownTypeError(streaminfo)
        self.ready_sem.release()
    
    def _message(self, bus, message):
        if not self.finished:
            if message.type == gst.MESSAGE_EOS:
                # The file is done. Tell the consumer thread.
                self.queue.put(SENTINEL)
            elif message.type == gst.MESSAGE_ERROR:
                gerror, debug = message.parse_error()
                if 'not-linked' in debug:
                    self.read_exc = NoStreamError()
                elif 'No such file' in debug:
                    self.read_exc = IOError('resource not found')
                else:
                    self.read_exc = FileReadError(debug)
                self.ready_sem.release()
    
    # Iteration.
    def next(self):
        # Wait for data from the Gstreamer callbacks.
        val = self.queue.get()
        if val == SENTINEL:
            # End of stream.
            raise StopIteration
        return val
    def __iter__(self):
        return self
    
    # Cleanup.
    def close(self, force=False):
        if self.running or force:
            self.running = False
            self.finished = True

            # Stop reading the file.
            self.dec.set_property("uri", None)
            # Block spurious signals.
            self.sink.get_pad("sink").disconnect(self.caps_handler)

            # Make space in the output queue to let the decoder thread
            # finish. (Otherwise, the thread blocks on its enqueue and
            # the interpreter hangs.)
            try:
                self.queue.get_nowait()
            except Queue.Empty:
                pass

            # Halt the pipeline (closing file).
            self.pipeline.set_state(gst.STATE_NULL)

    def __del__(self):
        self.close()
    
    # Context manager.
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        self.close()
        return False

# Smoke test.
if __name__ == '__main__':
    for path in sys.argv[1:]:
        path = os.path.abspath(os.path.expanduser(path))
        with GstAudioFile(path) as f:
            print f.channels
            print f.samplerate
            print f.duration
            for s in f:
                print len(s), ord(s[0])