Hello.
I have an h.264 encoding webcam, and I am trying to make it
work. Currently, it outputs a valid h.264 stream, but each frame
is compressed to ~12K of data, resulting in a very distorted, but
still barely recognizable image. I suppose that some of the XU controls
are responsible for the encoding quality, and they're in some extreme
position by default.
The webcam is "046d:0828 Logitech, Inc. HD Webcam B990".
Here are the XU descriptors (whole `lsusb -v' is 52K long, and I'm not
sure if I really should post it to the list):
----%<----%<----%<----%<----%<----%<----
VideoControl Interface Descriptor:
bLength 27
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 3
guidExtensionCode
{e48e6769-0f41-db40-a850-7420d7d8240e}
bNumControl 9
bNrPins 1
baSourceID( 0) 2
bControlSize 2
bmControls( 0) 0x3f
bmControls( 1) 0x07
iExtension 0
VideoControl Interface Descriptor:
bLength 26
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 4
guidExtensionCode
{1502e449-34f4-fe47-b158-0e885023e51b}
bNumControl 2
bNrPins 1
baSourceID( 0) 2
bControlSize 1
bmControls( 0) 0x03
iExtension 0
VideoControl Interface Descriptor:
bLength 28
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 6
guidExtensionCode
{a94c5d1f-11de-8744-840d-50933c8ec8d1}
bNumControl 20
bNrPins 1
baSourceID( 0) 4
bControlSize 3
bmControls( 0) 0xff
bmControls( 1) 0xff
bmControls( 2) 0x1f
iExtension 0
VideoControl Interface Descriptor:
bLength 27
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 7
guidExtensionCode
{212de5ff-3080-2c4e-82d9-f587d00540bd}
bNumControl 6
bNrPins 1
baSourceID( 0) 4
bControlSize 2
bmControls( 0) 0x00
bmControls( 1) 0x3f
iExtension 0
VideoControl Interface Descriptor:
bLength 27
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 8
guidExtensionCode
{b600cd9a-4adc-bd4b-bdf8-5ffbb0c0d366}
bNumControl 6
bNrPins 1
baSourceID( 0) 4
bControlSize 2
bmControls( 0) 0x3f
bmControls( 1) 0x00
iExtension 0
VideoControl Interface Descriptor:
bLength 27
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 9
guidExtensionCode
{a032c549-154f-fc4c-908a-5bce154b1cea}
bNumControl 3
bNrPins 1
baSourceID( 0) 4
bControlSize 2
bmControls( 0) 0x07
bmControls( 1) 0x00
iExtension 0
VideoControl Interface Descriptor:
bLength 27
bDescriptorType 36
bDescriptorSubtype 6 (EXTENSION_UNIT)
bUnitID 10
guidExtensionCode
{41769ea2-04de-e347-8b2b-f4341aff003b}
bNumControl 9
bNrPins 1
baSourceID( 0) 4
bControlSize 2
bmControls( 0) 0xcf
bmControls( 1) 0x0b
iExtension 0
----%<----%<----%<----%<----%<----%<----
I've googled all the GUIDs, and it turned out that first four of them
also appear in lsusb listings for non-encoding webcams as well. So, I
decided that some of the other three contain the quality control. (It
may not be true, of course, but that's what I will start with.) They
have
19 different controls, apparently.
Now, I am trying to tune some of these with UVC, with no success. Here
is
the relevant code:
----%<----%<----%<----%<----%<----%<----
void init_controls()
{
struct uvc_xu_control_mapping mapping = {
.id = XU_START,
.name = "XU control",
.selector = 1,
.size = 1,
.offset = 0,
.v4l2_type = V4L2_CTRL_TYPE_INTEGER,
.data_type = UVC_CTRL_DATA_TYPE_SIGNED,
};
guid_to_byte_array("{a032c549-154f-fc4c-908a-5bce154b1cea}",
mapping.entity);
if(ioctl(fd, UVCIOC_CTRL_MAP, &mapping) < 0) {
fprintf(stderr, "Cannot add control: %d, %s\n",
errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
----%<----%<----%<----%<----%<----%<----
(The `guid_to_byte_array' function was taken from libwebcam
sources. Handcrafting the GUID with proper endianness gives
the same result).
It outputs: Cannot add control: 2, No such file or directory
I've examined USB bus transactions. They include a control `request'
and an interrupt `reply'.
The control frame is here:
bmRequestType: 0x21
bRequest: 1
wValue: 0x0200
wIndex: 1
wLength: 26
This is somewhat strange. Per sect. 4.2.2.4 of UVC1.1 spec,
bmRequestType=0x21 and bRequest=1 indicate a SET_CUR transfer.
wValue of 0x0200 addresses selects control 2 instead of 1 (through
this is still in range), and wIndex selects XU 1 (while my one
has bUnitID of 8). Also, I do not understand at all what does the
data transmitted means:
00:00:01:01:00:00:00:00
00:00:00:00:00:00:00:00
32:00:00:60:09:00:00:0c
00:00
The reply contains a -ENOENT (-2) code, as shown by Wireshark.
Using different GUID's or different selectors does not change
anything.
What am I doing wrong here?
--
WBR, Peter Zotov.
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