Thanks for the comments and explanation.
On 13/09/10 00:11, Laurent Pinchart wrote:
> Hi Martin,
>
> On Friday 27 August 2010 16:14:52 Martin wrote:
>> The problem:
[...]
> The webcam sends a frame at high speed and then waits a (relatively) long
> time
> before sending the next frame.
>
>> *A possible solution* ?
>>
>> Instead, could the UVC driver 'simulate' a reduced framerate by instead
>> using the "STILL_IMAGE_FRAME" mode of the webcam and grab for itself a
>> set number of images per second? Or even only when polled by a read from
>> the user application?
>
> Still image capture isn't supported yet. The reason is that most webcams just
> ask the driver to take the next picture in the video stream to emulate still
> image capture. Very few cameras support out-of-band still image capture, and
> I
> don't own any that support that.
>
> As most cameras just ask the driver to capture the next frame in an active
> video stream this won't solve your problem anyway.
That's quite a shame... And very wasteful of bandwidth.
I guess we need slightly more expensive webcams that buffer an image
into local ram before forwarding it on at whatever USB rate might be
available. No go on that one I guess...
>> Further details:
>>
>> I'm trying to use two webcams simultaneously:
>>
>> iManufacturer 1 Sweex
>> iProduct 2 WC060 Series HD Webcam
>
> Please post the whole USB descriptors (lsusb -v)
I've attached "lsusb -v -d 177f:0060".
[...]
>> Can I tweak the UVC driver to preferentially choose the slower frame
>> rate available?
>
> You can select a frame rate explictly with VIDIOC_S_PARM.
>
>> Aside: The MJPG format doesn't seem to work, nor are any compression
>> settings visible...
>
> Maybe your webcam doesn't support MJPG.
>
>> Given a few hints or a patch, I can hack the kernel module to test :-)
>>
>> This is running on Gentoo, kernel 2.6.34 using the in-kernel uvc module.
>>
>> Any comment/ideas welcomed.
>
> If you don't need to capture frames simultaneously, you can just start the
> video stream, capture a frame, stop the video stream, and repeat the sequence
> on the second webcam.
>
> If you need higher frame rates, search the mailing list archives for
> discussions about bandwidth (dwMaxPayloadTransferSize is a keyword). You can
> also have a look at the "Multiple camera framerate." mail thread started by
> Dennis Muhlestein.
Thanks for the pointers.
I've had mixed results with (bash):
while true
do
ffmpeg -v 5 -y -r 5 -vframes 2 -s xga -f video4linux2 -i /dev/video0
-sameq -f image2 foo0-%03d.jpg
sleep 5
ffmpeg -v 5 -y -r 5 -vframes 2 -s xga -f video4linux2 -i /dev/video1
-sameq -f image2 foo1-%03d.jpg
sleep 5
date -R
done
That sometimes works fine, and then can randomly freeze at the point
where ffmpeg is to capture a frame. Usually, the freeze-up scenario is
that /dev/video0 is captured fine and then ffmpeg freezes on /dev/video1.
The "-r 5" may well not be needed. "-vframes 1" also works for if you
just want one frame, although I've found the first frame can be
overexposed compared to the following frames.
Not sure if -sameq is doing anything. Trying -bitexact always caused an
error for the options.
The "sleep 5" appears to help to allow operation for longer (a minute or
so) before ffmpeg freezing.
Running ffmpeg manually, one webcam at a time usually works fine.
Using "-r 30 -s vga" for the default framerate and 640x480 always works...
So... Is there some timing race or other untidiness whereby ffmpeg jams
or the video stream otherwise doesn't start?
I've only got one PCI slot... Are there any PCI cards with multiple
separate USB hubs?! (I suspect not...)
Regards,
Martin
Bus 002 Device 003: ID 177f:0060
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 239 Miscellaneous Device
bDeviceSubClass 2 ?
bDeviceProtocol 1 Interface Association
bMaxPacketSize0 64
idVendor 0x177f
idProduct 0x0060
bcdDevice 1.00
iManufacturer 1 Sweex
iProduct 2 WC060 Series HD Webcam
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 1125
bNumInterfaces 4
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 128mA
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 0
bInterfaceCount 2
bFunctionClass 14 Video
bFunctionSubClass 3 Video Interface Collection
bFunctionProtocol 0
iFunction 2 WC060 Series HD Webcam
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 14 Video
bInterfaceSubClass 1 Video Control
bInterfaceProtocol 0
iInterface 2 WC060 Series HD Webcam
VideoControl Interface Descriptor:
bLength 13
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdUVC 1.00
wTotalLength 79
dwClockFrequency 30.000000MHz
bInCollection 1
baInterfaceNr( 0) 1
VideoControl Interface Descriptor:
bLength 18
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 1
wTerminalType 0x0201 Camera Sensor
bAssocTerminal 0
iTerminal 0
wObjectiveFocalLengthMin 0
wObjectiveFocalLengthMax 0
wOcularFocalLength 0
bControlSize 3
bmControls 0x0000000a
Auto-Exposure Mode
Exposure Time (Absolute)
VideoControl Interface Descriptor:
bLength 11
bDescriptorType 36
bDescriptorSubtype 5 (PROCESSING_UNIT)
Warning: Descriptor too short
bUnitID 2
bSourceID 1
wMaxMultiplier 0
bControlSize 2
bmControls 0x0000177b
Brightness
Contrast
Saturation
Sharpness
Gamma
White Balance Temperature
Backlight Compensation
Gain
Power Line Frequency
White Balance Temperature, Auto
iProcessing 0
bmVideoStandards 0x 9
None
SECAM - 625/50
VideoControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 3
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bSourceID 2
iTerminal 0
VideoControl Interface Descriptor:
bLength 28
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 4
guidExtensionCode {e3deaebb-c2ec-4d42-802c-72f2eb3dfb57}
bNumControl 8
bNrPins 1
baSourceID( 0) 1
bControlSize 3
bmControls( 0) 0x59
bmControls( 1) 0x80
bmControls( 2) 0x80
iExtension 0
Endpoint Descriptor:
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bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x000a 1x 10 bytes
bInterval 5
Interface Descriptor:
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bDescriptorType 4
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bInterfaceClass 14 Video
bInterfaceSubClass 2 Video Streaming
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iInterface 0
VideoStreaming Interface Descriptor:
bLength 15
bDescriptorType 36
bDescriptorSubtype 1 (INPUT_HEADER)
bNumFormats 2
wTotalLength 761
bEndPointAddress 130
bmInfo 0
bTerminalLink 3
bStillCaptureMethod 2
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bTriggerUsage 1
bControlSize 1
bmaControls( 0) 27
bmaControls( 1) 27
VideoStreaming Interface Descriptor:
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bDescriptorSubtype 4 (FORMAT_UNCOMPRESSED)
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guidFormat
{59555932-0000-1000-8000-00aa00389b71}
bBitsPerPixel 16
bDefaultFrameIndex 1
bAspectRatioX 0
bAspectRatioY 0
bmInterlaceFlags 0x00
Interlaced stream or variable: No
Fields per frame: 1 fields
Field 1 first: No
Field pattern: Field 1 only
bCopyProtect 0
VideoStreaming Interface Descriptor:
bLength 34
bDescriptorType 36
bDescriptorSubtype 5 (FRAME_UNCOMPRESSED)
bFrameIndex 1
bmCapabilities 0x00
Still image unsupported
wWidth 640
wHeight 480
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 614400
dwDefaultFrameInterval 333333
bFrameIntervalType 2
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dwFrameInterval( 1) 666667
VideoStreaming Interface Descriptor:
bLength 34
bDescriptorType 36
bDescriptorSubtype 5 (FRAME_UNCOMPRESSED)
bFrameIndex 2
bmCapabilities 0x00
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dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 202752
dwDefaultFrameInterval 333333
bFrameIntervalType 2
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dwFrameInterval( 1) 666667
VideoStreaming Interface Descriptor:
bLength 34
bDescriptorType 36
bDescriptorSubtype 5 (FRAME_UNCOMPRESSED)
bFrameIndex 3
bmCapabilities 0x00
Still image unsupported
wWidth 320
wHeight 240
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 153600
dwDefaultFrameInterval 333333
bFrameIntervalType 2
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dwFrameInterval( 1) 666667
VideoStreaming Interface Descriptor:
bLength 34
bDescriptorType 36
bDescriptorSubtype 5 (FRAME_UNCOMPRESSED)
bFrameIndex 4
bmCapabilities 0x00
Still image unsupported
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wHeight 144
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 50688
dwDefaultFrameInterval 333333
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
bDescriptorSubtype 5 (FRAME_UNCOMPRESSED)
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bmCapabilities 0x00
Still image unsupported
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wHeight 120
dwMinBitRate 768000
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dwMaxVideoFrameBufferSize 38400
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
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bmCapabilities 0x00
Still image unsupported
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dwMinBitRate 768000
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dwDefaultFrameInterval 1333333
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
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bmCapabilities 0x00
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wHeight 1024
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dwMaxVideoFrameBufferSize 2621440
dwDefaultFrameInterval 1333333
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
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bmCapabilities 0x00
Still image unsupported
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dwMinBitRate 768000
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dwMaxVideoFrameBufferSize 3840000
dwDefaultFrameInterval 2000000
bFrameIntervalType 2
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VideoStreaming Interface Descriptor:
bLength 42
bDescriptorType 36
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bNumCompressionPatterns 9
VideoStreaming Interface Descriptor:
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bColorPrimaries 1 (BT.709,sRGB)
bTransferCharacteristics 1 (BT.709)
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VideoStreaming Interface Descriptor:
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Fixed-size samples: Yes
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bAspectRatioY 0
bmInterlaceFlags 0x00
Interlaced stream or variable: No
Fields per frame: 1 fields
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Field pattern: Field 1 only
bCopyProtect 0
VideoStreaming Interface Descriptor:
bLength 34
bDescriptorType 36
bDescriptorSubtype 7 (FRAME_MJPEG)
bFrameIndex 1
bmCapabilities 0x00
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wHeight 480
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 614400
dwDefaultFrameInterval 666667
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
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bDescriptorType 36
bDescriptorSubtype 7 (FRAME_MJPEG)
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bmCapabilities 0x00
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wHeight 240
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 153600
dwDefaultFrameInterval 666667
bFrameIntervalType 2
dwFrameInterval( 0) 666667
dwFrameInterval( 1) 1333333
VideoStreaming Interface Descriptor:
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bDescriptorType 36
bDescriptorSubtype 7 (FRAME_MJPEG)
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bmCapabilities 0x00
Still image unsupported
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wHeight 144
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 50688
dwDefaultFrameInterval 666667
bFrameIntervalType 2
dwFrameInterval( 0) 666667
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
bDescriptorSubtype 7 (FRAME_MJPEG)
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bmCapabilities 0x00
Still image unsupported
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wHeight 120
dwMinBitRate 768000
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dwMaxVideoFrameBufferSize 38400
dwDefaultFrameInterval 666667
bFrameIntervalType 2
dwFrameInterval( 0) 666667
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VideoStreaming Interface Descriptor:
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bDescriptorType 36
bDescriptorSubtype 7 (FRAME_MJPEG)
bFrameIndex 6
bmCapabilities 0x00
Still image unsupported
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wHeight 600
dwMinBitRate 768000
dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 960000
dwDefaultFrameInterval 666667
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bDescriptorType 36
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bmCapabilities 0x00
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wHeight 960
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dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 2457600
dwDefaultFrameInterval 666667
bFrameIntervalType 2
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dwFrameInterval( 1) 1333333
VideoStreaming Interface Descriptor:
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bDescriptorType 36
bDescriptorSubtype 7 (FRAME_MJPEG)
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bmCapabilities 0x00
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dwMaxVideoFrameBufferSize 2621440
dwDefaultFrameInterval 666667
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VideoStreaming Interface Descriptor:
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bDescriptorSubtype 7 (FRAME_MJPEG)
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bmCapabilities 0x00
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wHeight 1200
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dwMaxBitRate 196608000
dwMaxVideoFrameBufferSize 3840000
dwDefaultFrameInterval 666667
bFrameIntervalType 2
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dwFrameInterval( 1) 1333333
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wHeight( 6) 960
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VideoStreaming Interface Descriptor:
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bDescriptorSubtype 13 (COLORFORMAT)
bColorPrimaries 1 (BT.709,sRGB)
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Interface Descriptor:
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bInterfaceSubClass 2 Video Streaming
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bInterfaceSubClass 2 Video Streaming
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bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
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Endpoint Descriptor:
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bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
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Transfer Type Isochronous
Synch Type Asynchronous
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bInterval 1
Interface Association:
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bDescriptorType 11
bFirstInterface 2
bInterfaceCount 2
bFunctionClass 1 Audio
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bFunctionProtocol 0
iFunction 3 WC060 Series HD Webcam (Audio)
Interface Descriptor:
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bInterfaceNumber 2
bAlternateSetting 0
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bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
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iInterface 3 WC060 Series HD Webcam (Audio)
AudioControl Interface Descriptor:
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bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 1
wTerminalType 0x0201 Microphone
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wChannelConfig 0x0000
iChannelNames 0
iTerminal 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 2
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bmaControls( 0) 0x00
bmaControls( 1) 0x03
Mute
Volume
iFeature 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 3
wTerminalType 0x0101 USB Streaming
bAssocTerminal 1
bSourceID 2
iTerminal 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
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Interface Descriptor:
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bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 0
iInterface 0
AudioStreaming Interface Descriptor:
bLength 7
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
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bDelay 1 frames
wFormatTag 1 PCM
AudioStreaming Interface Descriptor:
bLength 29
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
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bSubframeSize 2
bBitResolution 16
bSamFreqType 7 Discrete
tSamFreq[ 0] 8000
tSamFreq[ 1] 11025
tSamFreq[ 2] 16000
tSamFreq[ 3] 22050
tSamFreq[ 4] 32000
tSamFreq[ 5] 44100
tSamFreq[ 6] 48000
Endpoint Descriptor:
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bDescriptorType 5
bEndpointAddress 0x83 EP 3 IN
bmAttributes 1
Transfer Type Isochronous
Synch Type None
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bInterval 4
bRefresh 0
bSynchAddress 0
AudioControl Endpoint Descriptor:
bLength 7
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x01
Sampling Frequency
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wLockDelay 0 Undefined
Device Qualifier (for other device speed):
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bDescriptorType 6
bcdUSB 2.00
bDeviceClass 239 Miscellaneous Device
bDeviceSubClass 2 ?
bDeviceProtocol 1 Interface Association
bMaxPacketSize0 64
bNumConfigurations 1
Device Status: 0x0000
(Bus Powered)
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