wavinfo/wavinfo/wave_reader.py

#-*- coding: utf-8 -*-
import struct
import os
import sys
from collections import namedtuple

if sys.version[0] == '3':
    import pathlib
else:
    import urlparse, urllib

from .riff_parser import parse_chunk, ChunkDescriptor, ListChunkDescriptor
from .wave_ixml_reader import WavIXMLFormat
from .wave_bext_reader import WavBextReader
from .wave_info_reader import WavInfoChunkReader

#: Calculated statistics about the audio data.
WavDataDescriptor = namedtuple('WavDataDescriptor','byte_count frame_count')

#: The format of the audio samples.
WavAudioFormat = namedtuple('WavAudioFormat','audio_format channel_count sample_rate byte_rate block_align bits_per_sample')

class WavInfoReader():
    """
    Parse a WAV audio file for metadata.
    """

    def __init__(self, path, info_encoding='latin_1', bext_encoding='ascii'):
        """
        Create a new reader object.

        :param path: A filesystem path to the wav file you wish to probe.

        :param info_encoding: The text encoding of the INFO metadata fields.
          latin_1/Win CP1252 has always been a pretty good guess for this.

        :param bext_encoding: The text encoding to use when decoding the string
          fields of the Broadcast-WAV extension. Per EBU 3285 this is ASCII
          but this parameter is available to you if you encounter a werido.
        """
        absolute_path = os.path.abspath(path)

        if sys.version[0] == '3':
            #: `file://` url for the file.
            self.url = pathlib.Path(absolute_path).as_uri()
        else:
            self.url = urlparse.urljoin('file:', urllib.pathname2url(absolute_path))

        with open(path, 'rb') as f:
            chunks = parse_chunk(f)

            self.main_list = chunks.children
            f.seek(0)

            #: :class:`wavinfo.wave_reader.WavAudioFormat`
            self.fmt    = self._get_format(f)

            #: :class:`wavinfo.wave_bext_reader.WavBextReader` with Broadcast-WAV metadata
            self.bext   = self._get_bext(f, encoding=bext_encoding)

            #: :class:`wavinfo.wave_ixml_reader.WavIXMLFormat` with iXML metadata
            self.ixml   = self._get_ixml(f)

            #: :class:`wavinfo.wave_info_reader.WavInfoChunkReader` with RIFF INFO metadata
            self.info   = self._get_info(f, encoding=info_encoding)
            self.data   = self._describe_data(f)

    def _find_chunk_data(self, ident, from_stream, default_none=False):
        chunk_descriptor = None
        top_chunks = (chunk for chunk in self.main_list if type(chunk) is ChunkDescriptor)

        if default_none:
            chunk_descriptor = next((chunk for chunk in top_chunks if chunk.ident == ident),None)
        else:
            chunk_descriptor = next((chunk for chunk in top_chunks if chunk.ident == ident))

        if chunk_descriptor:
            return chunk_descriptor.read_data(from_stream)
        else:
            return None


    def _describe_data(self,f):
        data_chunk = next(c for c in self.main_list if c.ident == b'data')

        return WavDataDescriptor(byte_count= data_chunk.length,
                frame_count= int(data_chunk.length / self.fmt.block_align))


    def _get_format(self,f):
        fmt_data = self._find_chunk_data(b'fmt ',f)

        # The format chunk is
        # audio_format    U16
        # channel_count   U16
        # sample_rate     U32   Note an integer
        # byte_rate       U32   == SampleRate * NumChannels * BitsPerSample/8
        # block_align     U16   == NumChannels * BitsPerSample/8
        # bits_per_sampl  U16
        packstring = "<HHIIHH"
        rest_starts = struct.calcsize(packstring)

        unpacked = struct.unpack(packstring, fmt_data[:rest_starts])

        #0x0001	WAVE_FORMAT_PCM	PCM
        #0x0003	WAVE_FORMAT_IEEE_FLOAT	IEEE float
        #0x0006	WAVE_FORMAT_ALAW	8-bit ITU-T G.711 A-law
        #0x0007	WAVE_FORMAT_MULAW	8-bit ITU-T G.711 µ-law
        #0xFFFE	WAVE_FORMAT_EXTENSIBLE	Determined by SubFormat

        #https://sno.phy.queensu.ca/~phil/exiftool/TagNames/RIFF.html
        return WavAudioFormat(audio_format = unpacked[0],
                    channel_count   = unpacked[1],
                    sample_rate     = unpacked[2],
                    byte_rate       = unpacked[3],
                    block_align     = unpacked[4],
                    bits_per_sample = unpacked[5]
                    )

    def _get_info(self, f, encoding):
        finder = (chunk.signature for chunk in self.main_list \
                if type(chunk) is ListChunkDescriptor)

        if b'INFO' in finder:
            return WavInfoChunkReader(f, encoding)

    def _get_bext(self, f, encoding):
        bext_data = self._find_chunk_data(b'bext',f,default_none=True)
        if bext_data:
            return WavBextReader(bext_data, encoding)
        else:
            return None

    def _get_ixml(self,f):
        ixml_data = self._find_chunk_data(b'iXML',f,default_none=True)
        if ixml_data is None:
            return None

        ixml_string = ixml_data.rstrip(b'\0')
        return WavIXMLFormat(ixml_string)

    def walk(self):
        """
        Walk all of the available metadata fields.

        :yields: a string, the :scope: of the metadatum, the string :name: of the
        metadata field, and the value.
        """

        scopes = ('fmt','data')#,'bext','ixml','info')

        for scope in scopes:
            attr = self.__getattribute__(scope)
            for field in attr._fields:
                yield scope, field, attr.__getattribute__(field)