bpo-32990: Support WAVE_FORMAT_EXTENSIBLE in the wave module

The test file, a modified version of
Lib/test/audiodata/pluck-pcm24.wav, was provided by Andrea Celletti
on the bug tracker.

Author: ZackerySpytz

Lib/test/audiodata/pluck-pcm24-ext.wav

@@ -78,6 +78,33 @@ class WavePCM24Test(WaveTest, unittest.TestCase):
         frames = byteswap(frames, 3)
 
 
+class WavePCM24ExtTest(WaveTest, unittest.TestCase):
+    sndfilename = 'pluck-pcm24-ext.wav'
+    sndfilenframes = 3307
+    nchannels = 2
+    sampwidth = 3
+    framerate = 11025
+    nframes = 48
+    comptype = 'NONE'
+    compname = 'not compressed'
+    frames = bytes.fromhex("""\
+      022D65FFEB9D 4B5A0F00FA54 3113C304EE2B 80DCD6084303 \
+      CBDEC006B261 48A99803F2F8 BFE82401B07D 036BFBFE7B5D \
+      B85756FA3EC9 B4B055F3502B 299830EBCB62 1A5CA7E6D99A \
+      EDFA3EE491BD C625EBE27884 0E05A9E0B6CF EF2929E02922 \
+      5758D8E27067 FB3557E83E16 1377BFEF8402 D82C5BF7272A \
+      978F16FB7745 F5F865FC1013 086635FB9C4E DF30FCFB40EE \
+      117FE0FA3438 3EE6B8FB5AC3 BC77A3FCB2F4 66D6DAFF5F32 \
+      CF13B9041275 431D69097A8C C1BB600EC74E 5120B912A2BA \
+      EEDF641754C0 8207001664B7 7FFFFF14453F 8000001294E6 \
+      499C1B0EB3B2 52B73E0DBCA0 EFB2B20F5FD8 CE3CDB0FBE12 \
+      E4B49C0CEA2D 6344A80A5A7C 08C8FE0A1FFE 2BB9860B0A0E \
+      51486F0E44E1 8BCC64113B05 B6F4EC0EEB36 4413170A5B48 \
+      """)
+    if sys.byteorder != 'big':
+        frames = byteswap(frames, 3)
+
+
 class WavePCM32Test(WaveTest, unittest.TestCase):
     sndfilename = 'pluck-pcm32.wav'
     sndfilenframes = 3307
@@ -109,7 +136,7 @@ class MiscTestCase(audiotests.AudioMiscTests, unittest.TestCase):
     module = wave
 
     def test__all__(self):
-        blacklist = {'WAVE_FORMAT_PCM'}
+        blacklist = {'WAVE_FORMAT_PCM', 'WAVE_FORMAT_EXTENSIBLE'}
         support.check__all__(self, wave, blacklist=blacklist)
 
 

Lib/test/test_wave.py

@@ -79,6 +79,7 @@ class Error(Exception):
     pass
 
 WAVE_FORMAT_PCM = 0x0001
+WAVE_FORMAT_EXTENSIBLE = 0xFFFE
 
 _array_fmts = None, 'b', 'h', None, 'i'
 
@@ -254,19 +255,22 @@ def readframes(self, nframes):
 
     def _read_fmt_chunk(self, chunk):
         try:
-            wFormatTag, self._nchannels, self._framerate, dwAvgBytesPerSec, wBlockAlign = struct.unpack_from('<HHLLH', chunk.read(14))
+            wFormatTag, self._nchannels, self._framerate, dwAvgBytesPerSec, \
+            wBlockAlign, wBitsPerSample = \
+                struct.unpack_from('<HHLLHH', chunk.read(16))
         except struct.error:
             raise EOFError from None
-        if wFormatTag == WAVE_FORMAT_PCM:
-            try:
-                sampwidth = struct.unpack_from('<H', chunk.read(2))[0]
-            except struct.error:
-                raise EOFError from None
-            self._sampwidth = (sampwidth + 7) // 8
-            if not self._sampwidth:
-                raise Error('bad sample width')
-        else:
+        if wFormatTag == WAVE_FORMAT_EXTENSIBLE:
+            # Only the first 2 bytes (of 16) of SubFormat are needed.
+            cbSize, wValidBitsPerSample, dwChannelMask, \
+            SubFormatFmt = struct.unpack_from('<HHLH', chunk.read(10))
+            if SubFormatFmt != WAVE_FORMAT_PCM:
+                raise Error(f'unknown format: {SubFormatFmt}')
+        elif wFormatTag != WAVE_FORMAT_PCM:
             raise Error('unknown format: %r' % (wFormatTag,))
+        self._sampwidth = (wBitsPerSample + 7) // 8
+        if not self._sampwidth:
+            raise Error('bad sample width')
         if not self._nchannels:
             raise Error('bad # of channels')
         self._framesize = self._nchannels * self._sampwidth

Lib/wave.py

@@ -0,0 +1,2 @@
+Support reading wave files with the ``WAVE_FORMAT_EXTENSIBLE`` format in the
+:mod:`wave` module.