[New-bugs-announce] [issue19131] Broken support of compressed AIFC files

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

In u-law and A-law compressed AIFC files the sampleSize field is equal to 8 (bits). The aifc module transparently compress/uncompress audio data to 16-bit, but doesn't support the samplewidth parameter in consistency. This causes two bugs:

1. On read getsampwidth() returns 1, but should return 2 (bytes per sample in uncompressed audio data). readframes() returns twice less data than expected.

>>> import aifc
>>> f = aifc.open('pluck-ulaw.aifc', 'r')
>>> f.getparams()
_aifc_params(nchannels=2, sampwidth=1, framerate=11025, nframes=3307, comptype=b'ulaw', compname=b'')
>>> f.readframes(1)
b',\x02'

f.readframes(1) should return 4 bytes (2 channels, 16-bit uncompressed data).

2. On write wrong value 2 is saved in the sampleSize field. Resulting file is invalid and can't be read in other programs.

Here is a patch and sample file. For tests see issue18919.

I'm sure G722 support is broken too, but I have no any testing files.

----------
components: Library (Lib)
files: aifc_sampwidth.patch
keywords: patch
messages: 198631
nosy: r.david.murray, serhiy.storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: Broken support of compressed AIFC files
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4
Added file: http://bugs.python.org/file31909/aifc_sampwidth.patch

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<http://bugs.python.org/issue19131>
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