files.py

"""Module that handles file access and decoding to PCM.

It uses python-audiotools for the majority of the work done."""
import os.path
import audiotools
import audiotools.mp3
import garbage


class AudioError(Exception):
    """Exception raised when an error occurs in this module."""
    pass


class GarbageAudioFile(garbage.Garbage):
    """Garbage class of the AudioFile class"""
    def collect(self):
        """Tries to close the AudioFile resources when called."""
        try:
            self.item._reader.close()
        except (audiotools.DecodingError):
            pass
        # Hack to kill zombies below
        import gc, subprocess
        try:
            [item.poll() for item in gc.get_referrers(subprocess.Popen)
             if isinstance(item, subprocess.Popen)]
        except:
            logger.warning("Exception occured in hack.")
        # Hack to kill zombies above
        
        return True
    
    
class AudioFile(object):
    """A Simple wrapper around the audiotools library.
    
    This opens the filename given wraps the file in a PCMConverter that
    turns it into PCM of format 44.1kHz, Stereo, 24-bit depth."""
    def __init__(self, filename):
        super(AudioFile, self).__init__()
        self._reader = self._open_file(filename)
        
    def read(self, size=4096, timeout=0.0):
        """Returns at most a string of size `size`.
        
        The `timeout` argument is unused. But kept in for compatibility with
        other read methods in the `audio` module."""
        return self._reader.read(size).to_bytes(False, True)
    
    def close(self):
        """Registers self for garbage collection. This method does not
        close anything and only registers itself for colleciton."""
        GarbageAudioFile(self)
        
    def __getattr__(self, key):
        try:
            return getattr(self._reader, key)
        except (AttributeError):
            return getattr(self.file, key)
        
    def progress(self, current, total):
        """Dummy progress function"""
        pass

    def _open_file(self, filename):
        """Open a file for reading and wrap it in several helpers."""
        _, ext = os.path.splitext(filename)
        if ext == '.mp3':
                opener = audiotools.mp3.MP3Audio
        else:
                opener = audiotools.open

        try:
            reader = opener(filename)
        except (audiotools.UnsupportedFile) as err:
            raise AudioError("Unsupported file: " + filename.encode('utf8'))
        except (ValueError) as err:
            raise AudioError("Unsupported file: " + filename.encode('utf8'))
        except:
            raise AudioError("Unsupported file: " + filename.encode('utf8'))

        
        self.file = reader
        total_frames = reader.total_frames()
        
        # Wrap in a PCMReader because we want PCM
        reader = reader.to_pcm()
        
        
        # Wrap in a converter
        reader = audiotools.PCMConverter(reader, sample_rate=44100,
                                    channels=2,
                                    channel_mask=audiotools.ChannelMask(0x1 | 0x2),
                                    bits_per_sample=24)
        
        # And for file progress!
        reader = audiotools.PCMReaderProgress(reader, total_frames,
                                              self.progress)
        
        return reader