V4l2

在linux下面有一组标准的API用于摄像头的采集，这个是一个采集框架叫做V4L（Video for Linux）,有大量的摄像头支持V4L框架，很多应用也支持通过该框架采集视频流。
树莓派的Raspberry Pi OS默认支持V4L2框架，名字叫做bcm2835-v4l2，可以通过v4l2-ctl工具集测试验证。

获取设备列表

martin@raspberrypi:~ $ v4l2-ctl --list-devices
bcm2835-codec-decode (platform:bcm2835-codec):/dev/video10/dev/video11/dev/video12/dev/video18/dev/video31/dev/media1bcm2835-isp (platform:bcm2835-isp):/dev/video13/dev/video14/dev/video15/dev/video16/dev/video20/dev/video21/dev/video22/dev/video23/dev/media0/dev/media2mmal service 16.1 (platform:bcm2835-v4l2-0):/dev/video0

驱动信息

martin@raspberrypi:~ $ v4l2-ctl -d /dev/video0 --all
Driver Info:Driver name      : bm2835 mmalCard type        : mmal service 16.1Bus info         : platform:bcm2835-v4l2-0Driver version   : 5.15.32Capabilities     : 0x85200005Video CaptureVideo OverlayRead/WriteStreamingExtended Pix FormatDevice CapabilitiesDevice Caps      : 0x05200005Video CaptureVideo OverlayRead/WriteStreamingExtended Pix Format
Priority: 2
Video input : 0 (Camera 0: ok)
Format Video Capture:Width/Height      : 1920/1080Pixel Format      : 'MJPG' (Motion-JPEG)Field             : NoneBytes per Line    : 0Size Image        : 2088960Colorspace        : SMPTE 170MTransfer Function : Default (maps to Rec. 709)YCbCr/HSV Encoding: Default (maps to ITU-R 601)Quantization      : Default (maps to Full Range)Flags             :
Format Video Overlay:Left/Top    : 150/50Width/Height: 1024/768Field       : NoneChroma Key  : 0x00000000Global Alpha: 0xffClip Count  : 0Clip Bitmap : No
Framebuffer Format:Capability    : Extern OverlayGlobal AlphaFlags         : Overlay Matches Capture/Output SizeWidth         : 1920Height        : 1088Pixel Format  : 'YU12'
Streaming Parameters Video Capture:Capabilities     : timeperframeFrames per second: 30.000 (30000/1000)Read buffers     : 1User Controlsbrightness 0x00980900 (int)    : min=0 max=100 step=1 default=50 value=50 flags=slidercontrast 0x00980901 (int)    : min=-100 max=100 step=1 default=0 value=0 flags=slidersaturation 0x00980902 (int)    : min=-100 max=100 step=1 default=0 value=0 flags=sliderred_balance 0x0098090e (int)    : min=1 max=7999 step=1 default=1000 value=1000 flags=sliderblue_balance 0x0098090f (int)    : min=1 max=7999 step=1 default=1000 value=1000 flags=sliderhorizontal_flip 0x00980914 (bool)   : default=0 value=0vertical_flip 0x00980915 (bool)   : default=0 value=0power_line_frequency 0x00980918 (menu)   : min=0 max=3 default=1 value=10: Disabled1: 50 Hz2: 60 Hz3: Autosharpness 0x0098091b (int)    : min=-100 max=100 step=1 default=0 value=0 flags=slidercolor_effects 0x0098091f (menu)   : min=0 max=15 default=0 value=00: None1: Black & White2: Sepia3: Negative4: Emboss5: Sketch6: Sky Blue7: Grass Green8: Skin Whiten9: Vivid10: Aqua11: Art Freeze12: Silhouette13: Solarization14: Antique15: Set Cb/Crrotate 0x00980922 (int)    : min=0 max=360 step=90 default=0 value=0 flags=modify-layoutcolor_effects_cbcr 0x0098092a (int)    : min=0 max=65535 step=1 default=32896 value=32896Codec Controlsvideo_bitrate_mode 0x009909ce (menu)   : min=0 max=1 default=0 value=0 flags=update0: Variable Bitrate1: Constant Bitratevideo_bitrate 0x009909cf (int)    : min=25000 max=25000000 step=25000 default=10000000 value=10000000repeat_sequence_header 0x009909e2 (bool)   : default=0 value=0force_key_frame 0x009909e5 (button) : flags=write-only, execute-on-writeh264_minimum_qp_value 0x00990a61 (int)    : min=0 max=51 step=1 default=0 value=0h264_maximum_qp_value 0x00990a62 (int)    : min=0 max=51 step=1 default=0 value=0h264_i_frame_period 0x00990a66 (int)    : min=0 max=2147483647 step=1 default=60 value=60h264_level 0x00990a67 (menu)   : min=0 max=13 default=11 value=110: 11: 1b2: 1.13: 1.24: 1.35: 26: 2.17: 2.28: 39: 3.110: 3.211: 412: 4.113: 4.2h264_profile 0x00990a6b (menu)   : min=0 max=4 default=4 value=40: Baseline1: Constrained Baseline2: Main4: HighCamera Controlsauto_exposure 0x009a0901 (menu)   : min=0 max=3 default=0 value=00: Auto Mode1: Manual Modeexposure_time_absolute 0x009a0902 (int)    : min=1 max=10000 step=1 default=1000 value=1000exposure_dynamic_framerate 0x009a0903 (bool)   : default=0 value=0auto_exposure_bias 0x009a0913 (intmenu): min=0 max=24 default=12 value=120: -4000 (0xfffffffffffff060)1: -3667 (0xfffffffffffff1ad)2: -3333 (0xfffffffffffff2fb)3: -3000 (0xfffffffffffff448)4: -2667 (0xfffffffffffff595)5: -2333 (0xfffffffffffff6e3)6: -2000 (0xfffffffffffff830)7: -1667 (0xfffffffffffff97d)8: -1333 (0xfffffffffffffacb)9: -1000 (0xfffffffffffffc18)10: -667 (0xfffffffffffffd65)11: -333 (0xfffffffffffffeb3)12: 0 (0x0)13: 333 (0x14d)14: 667 (0x29b)15: 1000 (0x3e8)16: 1333 (0x535)17: 1667 (0x683)18: 2000 (0x7d0)19: 2333 (0x91d)20: 2667 (0xa6b)21: 3000 (0xbb8)22: 3333 (0xd05)23: 3667 (0xe53)24: 4000 (0xfa0)white_balance_auto_preset 0x009a0914 (menu)   : min=0 max=10 default=1 value=10: Manual1: Auto2: Incandescent3: Fluorescent4: Fluorescent H5: Horizon6: Daylight7: Flash8: Cloudy9: Shade10: Greyworldimage_stabilization 0x009a0916 (bool)   : default=0 value=0iso_sensitivity 0x009a0917 (intmenu): min=0 max=4 default=0 value=00: 0 (0x0)1: 100000 (0x186a0)2: 200000 (0x30d40)3: 400000 (0x61a80)4: 800000 (0xc3500)iso_sensitivity_auto 0x009a0918 (menu)   : min=0 max=1 default=1 value=10: Manual1: Autoexposure_metering_mode 0x009a0919 (menu)   : min=0 max=3 default=0 value=00: Average1: Center Weighted2: Spot3: Matrixscene_mode 0x009a091a (menu)   : min=0 max=13 default=0 value=00: None8: Night11: SportsJPEG Compression Controlscompression_quality 0x009d0903 (int)    : min=1 max=100 step=1 default=30 value=30

支持格式

martin@raspberrypi:~ $ v4l2-ctl --list-formats
ioctl: VIDIOC_ENUM_FMTType: Video Capture[0]: 'YU12' (Planar YUV 4:2:0)[1]: 'YUYV' (YUYV 4:2:2)[2]: 'RGB3' (24-bit RGB 8-8-8)[3]: 'JPEG' (JFIF JPEG, compressed)[4]: 'H264' (H.264, compressed)[5]: 'MJPG' (Motion-JPEG, compressed)[6]: 'YVYU' (YVYU 4:2:2)[7]: 'VYUY' (VYUY 4:2:2)[8]: 'UYVY' (UYVY 4:2:2)[9]: 'NV12' (Y/CbCr 4:2:0)[10]: 'BGR3' (24-bit BGR 8-8-8)[11]: 'YV12' (Planar YVU 4:2:0)[12]: 'NV21' (Y/CrCb 4:2:0)[13]: 'RX24' (32-bit XBGR 8-8-8-8)

抓取JPEG图片

martin@raspberrypi:~ $ v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=3 && \
> v4l2-ctl --stream-mmap=3 --stream-count=1 --stream-to=1.jpg
<

录制264

martin@raspberrypi:~ $ v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=4 && v4l2-ctl --stream-mmap=3 --stream-count=100 --stream-to=1.h264
K<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.02 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<K< 30.02 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.02 fps
<<<<<<<<

FFMPEG

Pi预编译的ffmpeg已经支持依赖OpenMAX IL H264硬编解码。

sudo apt install -y ffmpeg

在树莓派上手动编译ffmpeg参考文章Compile FFmpeg with Hardware Accelerator

列出支持编码器

martin@raspberrypi:~ $ ffmpeg -encoders  | grep -E "264|mjpeg"V..... libx264              libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (codec h264)V..... libx264rgb           libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 RGB (codec h264)V..... h264_omx             OpenMAX IL H.264 video encoder (codec h264)V..... h264_v4l2m2m         V4L2 mem2mem H.264 encoder wrapper (codec h264)V..... h264_vaapi           H.264/AVC (VAAPI) (codec h264)VFS... mjpeg                MJPEG (Motion JPEG)V..... mjpeg_vaapi          MJPEG (VAAPI) (codec mjpeg)

编码器支持的格式

martin@raspberrypi:~ $ ffmpeg -h encoder=h264_omx
Encoder h264_omx [OpenMAX IL H.264 video encoder]:General capabilities: delayThreading capabilities: noneSupported pixel formats: yuv420p
h264_omx AVOptions:-omx_libname       <string>     ED.V...... OpenMAX library name-omx_libprefix     <string>     ED.V...... OpenMAX library prefix-zerocopy          <int>        E..V...... Try to avoid copying input frames if possible (from 0 to 1) (default 0)-profile           <int>        E..V...... Set the encoding profile (from -99 to 100) (default -99)baseline        66           E..V......main            77           E..V......high            100          E..V......

参考文献：Set up camera

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