https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192755
Bug ID: 192755
Summary: snd_uaudio incorrect handling of version 1 audio
format type descriptor
Product: Base System
Version: 10.0-STABLE
Hardware: amd64
OS: Any
Status: Needs Triage
Severity: Affects Only Me
Priority: ---
Component: usb
Assignee: [email protected]
Reporter: [email protected]
For USB audio 1.0 formats the code in uaudio.c uses the value of bBitResolution
from the descriptor directly to choose and internal audio format from the array
uaudio10_formats. It should use the value from bSubFrameSize instead.
It is clearly specified in the official USB document for audio data formats,
page 9 under the section "2.2.2 Audio Subframe" that the endpoint must be
handled using bSubFramSize*8 bits per sample from which the device will take
the number of bits it actually uses.
In my particular case I own a device reporting bBitResolution of 24 and
bSubFrameSize of 4. An unpatched driver will be sending 3-byte subframes to the
endpoint resulting in pure noise :)
For USB 2.0 formats the code already does some conversion to avoid this same
problem, using the equivalent bSubslotSize in the function
uaudio_chan_fill_info_sub:
/* Map 4-byte aligned 24-bit samples into 32-bit */
if (bBitResolution == 24 && bSubslotSize == 4)
bBitResolution = 32;
if (bBitResolution != (bSubslotSize * 8)) {
DPRINTF("Invalid bSubslotSize\n");
goto next_ep;
}
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