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: bLength 7 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: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 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 bTriggerSupport 1 bTriggerUsage 1 bControlSize 1 bmaControls( 0) 27 bmaControls( 1) 27 VideoStreaming Interface Descriptor: bLength 27 bDescriptorType 36 bDescriptorSubtype 4 (FORMAT_UNCOMPRESSED) bFormatIndex 1 bNumFrameDescriptors 9 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 dwFrameInterval( 0) 333333 dwFrameInterval( 1) 666667 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 2 bmCapabilities 0x00 Still image unsupported wWidth 352 wHeight 288 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 202752 dwDefaultFrameInterval 333333 bFrameIntervalType 2 dwFrameInterval( 0) 333333 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 dwFrameInterval( 0) 333333 dwFrameInterval( 1) 666667 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 4 bmCapabilities 0x00 Still image unsupported wWidth 176 wHeight 144 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 50688 dwDefaultFrameInterval 333333 bFrameIntervalType 2 dwFrameInterval( 0) 333333 dwFrameInterval( 1) 666667 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 5 bmCapabilities 0x00 Still image unsupported wWidth 160 wHeight 120 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 38400 dwDefaultFrameInterval 333333 bFrameIntervalType 2 dwFrameInterval( 0) 333333 dwFrameInterval( 1) 666667 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 6 bmCapabilities 0x00 Still image unsupported wWidth 800 wHeight 600 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 960000 dwDefaultFrameInterval 1000000 bFrameIntervalType 2 dwFrameInterval( 0) 1000000 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 7 bmCapabilities 0x00 Still image unsupported wWidth 1280 wHeight 960 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 2457600 dwDefaultFrameInterval 1333333 bFrameIntervalType 2 dwFrameInterval( 0) 1333333 dwFrameInterval( 1) 2000000 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 8 bmCapabilities 0x00 Still image unsupported wWidth 1280 wHeight 1024 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 2621440 dwDefaultFrameInterval 1333333 bFrameIntervalType 2 dwFrameInterval( 0) 1333333 dwFrameInterval( 1) 2000000 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) bFrameIndex 9 bmCapabilities 0x00 Still image unsupported wWidth 1600 wHeight 1200 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 3840000 dwDefaultFrameInterval 2000000 bFrameIntervalType 2 dwFrameInterval( 0) 2000000 dwFrameInterval( 1) 4000000 VideoStreaming Interface Descriptor: bLength 42 bDescriptorType 36 bDescriptorSubtype 3 (STILL_IMAGE_FRAME) bEndpointAddress 0 bNumImageSizePatterns 9 wWidth( 0) 640 wHeight( 0) 480 wWidth( 1) 352 wHeight( 1) 288 wWidth( 2) 320 wHeight( 2) 240 wWidth( 3) 176 wHeight( 3) 144 wWidth( 4) 160 wHeight( 4) 120 wWidth( 5) 800 wHeight( 5) 600 wWidth( 6) 1280 wHeight( 6) 960 wWidth( 7) 1280 wHeight( 7) 1024 wWidth( 8) 1600 wHeight( 8) 1200 bNumCompressionPatterns 9 VideoStreaming Interface Descriptor: bLength 6 bDescriptorType 36 bDescriptorSubtype 13 (COLORFORMAT) bColorPrimaries 1 (BT.709,sRGB) bTransferCharacteristics 1 (BT.709) bMatrixCoefficients 4 (SMPTE 170M (BT.601)) VideoStreaming Interface Descriptor: bLength 11 bDescriptorType 36 bDescriptorSubtype 6 (FORMAT_MJPEG) bFormatIndex 2 bNumFrameDescriptors 9 bFlags 1 Fixed-size samples: Yes 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 7 (FRAME_MJPEG) bFrameIndex 1 bmCapabilities 0x00 Still image unsupported wWidth 640 wHeight 480 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 614400 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 2 bmCapabilities 0x00 Still image unsupported wWidth 352 wHeight 288 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 202752 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 3 bmCapabilities 0x00 Still image unsupported wWidth 320 wHeight 240 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 153600 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 4 bmCapabilities 0x00 Still image unsupported wWidth 176 wHeight 144 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 50688 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 5 bmCapabilities 0x00 Still image unsupported wWidth 160 wHeight 120 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 38400 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 6 bmCapabilities 0x00 Still image unsupported wWidth 800 wHeight 600 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 960000 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 7 bmCapabilities 0x00 Still image unsupported wWidth 1280 wHeight 960 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 2457600 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 8 bmCapabilities 0x00 Still image unsupported wWidth 1280 wHeight 1024 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 2621440 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 34 bDescriptorType 36 bDescriptorSubtype 7 (FRAME_MJPEG) bFrameIndex 9 bmCapabilities 0x00 Still image unsupported wWidth 1600 wHeight 1200 dwMinBitRate 768000 dwMaxBitRate 196608000 dwMaxVideoFrameBufferSize 3840000 dwDefaultFrameInterval 666667 bFrameIntervalType 2 dwFrameInterval( 0) 666667 dwFrameInterval( 1) 1333333 VideoStreaming Interface Descriptor: bLength 42 bDescriptorType 36 bDescriptorSubtype 3 (STILL_IMAGE_FRAME) bEndpointAddress 0 bNumImageSizePatterns 9 wWidth( 0) 640 wHeight( 0) 480 wWidth( 1) 352 wHeight( 1) 288 wWidth( 2) 320 wHeight( 2) 240 wWidth( 3) 176 wHeight( 3) 144 wWidth( 4) 160 wHeight( 4) 120 wWidth( 5) 800 wHeight( 5) 600 wWidth( 6) 1280 wHeight( 6) 960 wWidth( 7) 1280 wHeight( 7) 1024 wWidth( 8) 1600 wHeight( 8) 1200 bNumCompressionPatterns 9 VideoStreaming Interface Descriptor: bLength 6 bDescriptorType 36 bDescriptorSubtype 13 (COLORFORMAT) bColorPrimaries 1 (BT.709,sRGB) bTransferCharacteristics 1 (BT.709) bMatrixCoefficients 4 (SMPTE 170M (BT.601)) Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 1 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x0080 1x 128 bytes bInterval 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 2 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x0200 1x 512 bytes bInterval 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 3 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x0400 1x 1024 bytes bInterval 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 4 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x0b00 2x 768 bytes bInterval 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 5 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x0c00 2x 1024 bytes bInterval 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 6 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x1380 3x 896 bytes bInterval 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 7 bNumEndpoints 1 bInterfaceClass 14 Video bInterfaceSubClass 2 Video Streaming bInterfaceProtocol 0 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x1400 3x 1024 bytes bInterval 1 Interface Association: bLength 8 bDescriptorType 11 bFirstInterface 2 bInterfaceCount 2 bFunctionClass 1 Audio bFunctionSubClass 2 Streaming bFunctionProtocol 0 iFunction 3 WC060 Series HD Webcam (Audio) Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 2 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 1 Control Device bInterfaceProtocol 0 iInterface 3 WC060 Series HD Webcam (Audio) AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 1 (HEADER) bcdADC 1.00 wTotalLength 39 bInCollection 1 baInterfaceNr( 0) 3 AudioControl Interface Descriptor: bLength 12 bDescriptorType 36 bDescriptorSubtype 2 (INPUT_TERMINAL) bTerminalID 1 wTerminalType 0x0201 Microphone bAssocTerminal 0 bNrChannels 1 wChannelConfig 0x0000 iChannelNames 0 iTerminal 0 AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 6 (FEATURE_UNIT) bUnitID 2 bSourceID 1 bControlSize 1 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 bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 3 bAlternateSetting 1 bNumEndpoints 1 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 0 AudioStreaming Interface Descriptor: bLength 7 bDescriptorType 36 bDescriptorSubtype 1 (AS_GENERAL) bTerminalLink 3 bDelay 1 frames wFormatTag 1 PCM AudioStreaming Interface Descriptor: bLength 29 bDescriptorType 36 bDescriptorSubtype 2 (FORMAT_TYPE) bFormatType 1 (FORMAT_TYPE_I) bNrChannels 1 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: bLength 9 bDescriptorType 5 bEndpointAddress 0x83 EP 3 IN bmAttributes 1 Transfer Type Isochronous Synch Type None Usage Type Data wMaxPacketSize 0x0062 1x 98 bytes bInterval 4 bRefresh 0 bSynchAddress 0 AudioControl Endpoint Descriptor: bLength 7 bDescriptorType 37 bDescriptorSubtype 1 (EP_GENERAL) bmAttributes 0x01 Sampling Frequency bLockDelayUnits 0 Undefined wLockDelay 0 Undefined Device Qualifier (for other device speed): bLength 10 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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