Linux v4l2子系统(9)：libv4l2
libv4l是一个对v4l2设备抽象层，包括一系列库文件和测试程序。
1 v4l2库文件
libv4l1.so：支持v4l1应用访问v4l2设备。
libv4l2.so：支持对v4l2设备的open/ioctl/close/poll等访问。
libv4l2convert.so：是为v4l2应用使用的libv4l2.so增加多种pixelformats的wrapper。
2 libv4l工具
3.1 media-ctl
用于获取以及配置v4l2设备：
media-ctl -d /dev/media1 -p
显示/dev/media1对应的Media设备拓扑结构如下，参考Media Graph：
Media controller API version 5.10.110 Media device information ------------------------ driver rkisp0-vir0 model rkisp0 serial bus info hw revision 0x0 driver version 5.10.110 Device topology - entity 1: rkisp-isp-subdev (4 pads, 10 links)--此Entity包含4个Pad，10个Link。 type V4L2 subdev subtype Unknown flags 0 device node name /dev/v4l-subdev3 pad0: Sink--此Sink可能有4个输入，当前Active输入是rkcif-mipi-lvds2。 [fmt:SBGGR10_1X10/2112x1568 field:none crop.bounds:(0,0)/2112x1568 crop:(0,0)/2112x1568] <- "rkisp_rawrd0_m":0 [] <- "rkisp_rawrd2_s":0 [] <- "rkisp_rawrd1_l":0 [] <- "rkcif-mipi-lvds2":0 [ENABLED] pad1: Sink <- "rkisp-input-params":0 [ENABLED] pad2: Source [fmt:YUYV8_2X8/2112x1568 field:none colorspace:smpte170m quantization:full-range crop.bounds:(0,0)/2112x1568 crop:(0,0)/2112x1568] -> "rkisp_mainpath":0 [ENABLED] -> "rkisp_selfpath":0 [ENABLED] -> "rkisp_fbcpath":0 [ENABLED] -> "rkisp_iqtool":0 [ENABLED] pad3: Source -> "rkisp-statistics":0 [ENABLED] - entity 6: rkisp_mainpath (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video11 pad0: Sink <- "rkisp-isp-subdev":2 [ENABLED] - entity 12: rkisp_selfpath (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video12 pad0: Sink <- "rkisp-isp-subdev":2 [ENABLED] - entity 18: rkisp_fbcpath (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video13 pad0: Sink <- "rkisp-isp-subdev":2 [ENABLED] - entity 24: rkisp_iqtool (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video14 pad0: Sink <- "rkisp-isp-subdev":2 [ENABLED] - entity 30: rkisp_rawrd0_m (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video15 pad0: Source -> "rkisp-isp-subdev":0 [] - entity 36: rkisp_rawrd2_s (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video16 pad0: Source -> "rkisp-isp-subdev":0 [] - entity 42: rkisp_rawrd1_l (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video17 pad0: Source -> "rkisp-isp-subdev":0 [] - entity 48: rkisp-statistics (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video18 pad0: Sink <- "rkisp-isp-subdev":3 [ENABLED] - entity 54: rkisp-input-params (1 pad, 1 link) type Node subtype V4L flags 0 device node name /dev/video19 pad0: Source -> "rkisp-isp-subdev":1 [ENABLED] - entity 60: rkcif-mipi-lvds2 (1 pad, 1 link)--此Entity包含1个Pad；一个Source Link，输出到rkisp-isp-subdev0。 type V4L2 subdev subtype Unknown flags 0 device node name /dev/v4l-subdev4 pad0: Source [fmt:SBGGR10_1X10/2112x1568@10000/300000 field:none] -> "rkisp-isp-subdev":0 [ENABLED]
3.2 v4l2-ctl
v44l2-ctl可以读取并配置v4l2设备的controls。
摄像头识别检测：
v4l2-ctl --list-devices
rk_hdmirx (fdee0000.hdmirx-controller):
/dev/video20
rkisp-statistics (platform: rkisp):
/dev/video18
/dev/video19
rkcif-mipi-lvds2 (platform:rkcif):
/dev/media0
rkcif (platform:rkcif-mipi-lvds2):
/dev/video0
/dev/video1
/dev/video2
/dev/video3
/dev/video4
/dev/video5
/dev/video6
/dev/video7
/dev/video8
/dev/video9
/dev/video10
rkisp_mainpath (platform:rkisp0-vir0):
/dev/video11
/dev/video12
/dev/video13
/dev/video14
/dev/video15
/dev/video16
/dev/video17
/dev/media1
查看摄像头支持的格式：
v4l2-ctl --list-formats-ext -d /dev/video11
ioctl: VIDIOC_ENUM_FMT
Type: Video Capture Multiplanar
[0]: 'UYVY' (UYVY 4:2:2)
Size: Stepwise 32x16 - 2112x1568 with step 8/8
[1]: 'NV16' (Y/CbCr 4:2:2)
Size: Stepwise 32x16 - 2112x1568 with step 8/8
[2]: 'NV61' (Y/CrCb 4:2:2)
Size: Stepwise 32x16 - 2112x1568 with step 8/8
[3]: 'NV21' (Y/CrCb 4:2:0)
Size: Stepwise 32x16 - 2112x1568 with step 8/8
[4]: 'NV12' (Y/CbCr 4:2:0)
Size: Stepwise 32x16 - 2112x1568 with step 8/8
[5]: 'NM21' (Y/CrCb 4:2:0 (N-C))
Size: Stepwise 32x16 - 2112x1568 with step 8/8
[6]: 'NM12' (Y/CbCr 4:2:0 (N-C))
Size: Stepwise 32x16 - 2112x1568 with step 8/8
摄像头采集格式查询：
v4l2-ctl -V -d /dev/video11
Format Video Capture Multiplanar:
Width/Height : 32/0
Pixel Format : 'UYVY' (UYVY 4:2:2)
Field : None
Number of planes : 1
Flags :
Colorspace : Default
Transfer Function : Default
YCbCr/HSV Encoding: Default
Quantization : Full Range
Plane 0 :
Bytes per Line : 64
Size Image : 0
摄像头图像预览：
gst-launch-1.0 v4l2src device=/dev/video11 ! \video/x-raw,format=NV12,width=640,height=480,framerate=30/1 ! autovideosink
摄像头录像：
v4l2-ctl -d /dev/video0 --set-fmt-video=width=1920,height=1080,pixelformat=1 --stream-mmap=3 --stream-count=20 --stream-to=/tmp/image.yuv --stream-out-pattern=1
3.3 v4l2-dbg
提供对v4l2设备的调试功能，主要通过设置VIDIOC_DBG_G_REGISTER/VIDIOC_DBG_S_REGISTER/VIDIOC_DBG_G_CHIP_INFO等ioctl命令。
3.4 v4l2-sysfs-path
检查当前系统的media设备并显示设备节点。
3.5 v4l2-compliance
对v4l2设备进行兼容性测试，对一系列ioctl命令进行有效性检查。
v4l2-compliance -d /dev/video11
参照RK3588 Media Graph分析如下：
v4l2-compliance 1.22.1, 64 bits, 64-bit time_t Compliance test for rkisp_v6 device /dev/video11: Driver Info: Driver name : rkisp_v6 Card type : rkisp_mainpath Bus info : platform:rkisp0-vir0--设备对应的总线和驱动。 Driver version : 2.0.0 Capabilities : 0x84201000 Video Capture Multiplanar Streaming Extended Pix Format Device Capabilities Device Caps : 0x04201000 Video Capture Multiplanar Streaming Extended Pix Format Media Driver Info: Driver name : rkisp0-vir0--驱动名称。 Model : rkisp0 Serial : Bus info : Media version : 5.10.110 Hardware revision: 0x00000000 (0) Driver version : 5.10.110 Interface Info: ID : 0x03000007 Type : V4L Video Entity Info: ID : 0x00000006 (6) Name : rkisp_mainpath--Media Graph Entity名称。 Function : V4L2 I/O Pad 0x01000009 : 0: Sink Link 0x0200000a: from remote pad 0x1000004 of entity 'rkisp-isp-subdev' (Unknown V4L2 Sub-Device): Data, Enabled--此Entity的Sink来源。 --下面是各种ioctl的检查，以及结查结果：OK表示功能正常，或者Not Supported。；FAIL表示失败，并指出失败位置。 Required ioctls: test MC information (see 'Media Driver Info' above): OK fail: v4l2-compliance.cpp(644): (vcap.version >> 16) < 3 test VIDIOC_QUERYCAP: FAIL fail: v4l2-compliance.cpp(783): doioctl(node, ioc, nullptr) != ENOTTY test invalid ioctls: FAIL Allow for multiple opens: test second /dev/video11 open: OK fail: v4l2-compliance.cpp(644): (vcap.version >> 16) < 3 test VIDIOC_QUERYCAP: FAIL test VIDIOC_G/S_PRIORITY: OK test for unlimited opens: OK Debug ioctls: test VIDIOC_DBG_G/S_REGISTER: OK (Not Supported) test VIDIOC_LOG_STATUS: OK (Not Supported) Input ioctls: test VIDIOC_G/S_TUNER/ENUM_FREQ_BANDS: OK (Not Supported) test VIDIOC_G/S_FREQUENCY: OK (Not Supported) test VIDIOC_S_HW_FREQ_SEEK: OK (Not Supported) test VIDIOC_ENUMAUDIO: OK (Not Supported) test VIDIOC_G/S/ENUMINPUT: OK (Not Supported) test VIDIOC_G/S_AUDIO: OK (Not Supported) Inputs: 0 Audio Inputs: 0 Tuners: 0 Output ioctls: test VIDIOC_G/S_MODULATOR: OK (Not Supported) test VIDIOC_G/S_FREQUENCY: OK (Not Supported) test VIDIOC_ENUMAUDOUT: OK (Not Supported) test VIDIOC_G/S/ENUMOUTPUT: OK (Not Supported) test VIDIOC_G/S_AUDOUT: OK (Not Supported) Outputs: 0 Audio Outputs: 0 Modulators: 0 Input/Output configuration ioctls: test VIDIOC_ENUM/G/S/QUERY_STD: OK (Not Supported) test VIDIOC_ENUM/G/S/QUERY_DV_TIMINGS: OK (Not Supported) test VIDIOC_DV_TIMINGS_CAP: OK (Not Supported) test VIDIOC_G/S_EDID: OK (Not Supported) Control ioctls: test VIDIOC_QUERY_EXT_CTRL/QUERYMENU: OK test VIDIOC_QUERYCTRL: OK test VIDIOC_G/S_CTRL: OK test VIDIOC_G/S/TRY_EXT_CTRLS: OK fail: v4l2-test-controls.cpp(872): subscribe event for control 'Image Processing Controls' failed test VIDIOC_(UN)SUBSCRIBE_EVENT/DQEVENT: FAIL test VIDIOC_G/S_JPEGCOMP: OK (Not Supported) Standard Controls: 2 Private Controls: 0 Format ioctls: test VIDIOC_ENUM_FMT/FRAMESIZES/FRAMEINTERVALS: OK test VIDIOC_G/S_PARM: OK (Not Supported) test VIDIOC_G_FBUF: OK (Not Supported) fail: v4l2-test-formats.cpp(358): !colorspace fail: v4l2-test-formats.cpp(481): testColorspace(!node->is_io_mc, pix_mp.pixelformat, pix_mp.colorspace, pix_mp.ycbcr_enc, pix_mp.quantization) test VIDIOC_G_FMT: FAIL fail: v4l2-test-formats.cpp(358): !colorspace fail: v4l2-test-formats.cpp(481): testColorspace(!node->is_io_mc, pix_mp.pixelformat, pix_mp.colorspace, pix_mp.ycbcr_enc, pix_mp.quantization) test VIDIOC_TRY_FMT: FAIL warn: v4l2-test-formats.cpp(1147): S_FMT cannot handle an invalid pixelformat. warn: v4l2-test-formats.cpp(1148): This may or may not be a problem. For more information see: warn: v4l2-test-formats.cpp(1149): http://www.mail-archive.com/linux-media@vger.kernel.org/msg56550.html fail: v4l2-test-formats.cpp(363): colorspace >= 0xff fail: v4l2-test-formats.cpp(481): testColorspace(!node->is_io_mc, pix_mp.pixelformat, pix_mp.colorspace, pix_mp.ycbcr_enc, pix_mp.quantization) test VIDIOC_S_FMT: FAIL test VIDIOC_G_SLICED_VBI_CAP: OK (Not Supported) fail: v4l2-test-formats.cpp(1517): doioctl(node, VIDIOC_G_SELECTION, &sel) != EINVAL test Cropping: FAIL test Composing: OK (Not Supported) test Scaling: OK Codec ioctls: test VIDIOC_(TRY_)ENCODER_CMD: OK (Not Supported) test VIDIOC_G_ENC_INDEX: OK (Not Supported) test VIDIOC_(TRY_)DECODER_CMD: OK (Not Supported) Buffer ioctls: fail: v4l2-test-buffers.cpp(607): q.reqbufs(node, 1) test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: FAIL fail: v4l2-test-buffers.cpp(783): VIDIOC_EXPBUF is supported, but the V4L2_MEMORY_MMAP support is missing or malfunctioning. fail: v4l2-test-buffers.cpp(784): VIDIOC_EXPBUF is supported, but the V4L2_MEMORY_MMAP support is missing, probably due to earlier failing format tests. test VIDIOC_EXPBUF: OK (Not Supported) test Requests: OK (Not Supported) Total for rkisp_v6 device /dev/video11: 46, Succeeded: 37, Failed: 9, Warnings: 3
3.6 qv4l2
qv4l2可以对Linux下v4l2设备进行调试、预览、录制。
3.7 v4l2grab
v4l2grab用于从v4l2设备抓图图像：
v4l2grab --device /dev/video11 -W 2112 -H 1568 -o test.jpeg -q 100
联系方式:arnoldlu@qq.com
