ubuntu - 具有 ffmpeg 和 v4l2loopback 的 yuva420p 等效的未知 V4L2 像素格式

Question

我正在尝试使用 ffmpeg 中的 filter_complex 将多个视频输入拼接到一个输出中。

我使用 v4l2loopback 创建一个虚拟视频设备:

sudo modprobe v4l2loopback video_nr=90

在此示例中，我首先尝试仅使用一台相机:
v4l2-ctl --device=/dev/video0 --info 给出以下输出:

Driver Info (not using libv4l2):
        Driver name   : uvcvideo
        Card type     : HD USB Camera
        Bus info      : usb-0000:00:14.0-13.2
        Driver version: 4.10.17
        Capabilities  : 0x84200001
                Video Capture
                Streaming
                Extended Pix Format
                Device Capabilities
        Device Caps   : 0x04200001
                Video Capture
                Streaming
                Extended Pix Format
Priority: 2
Video input : 0 (Camera 1: ok)
Format Video Capture:
        Width/Height      : 640/480
        Pixel Format      : 'YUYV'
        Field             : None
        Bytes per Line    : 1280
        Size Image        : 614400
        Colorspace        : sRGB
        Transfer Function : Default
        YCbCr Encoding    : Default
        Quantization      : Default
        Flags             :
Crop Capability Video Capture:
        Bounds      : Left 0, Top 0, Width 640, Height 480
        Default     : Left 0, Top 0, Width 640, Height 480
        Pixel Aspect: 1/1
Selection: crop_default, Left 0, Top 0, Width 640, Height 480
Selection: crop_bounds, Left 0, Top 0, Width 640, Height 480
Streaming Parameters Video Capture:
        Capabilities     : timeperframe
        Frames per second: 30.000 (30/1)
        Read buffers     : 0
                     brightness (int)    : min=0 max=15 step=1 default=8 value=8
                       contrast (int)    : min=0 max=15 step=1 default=8 value=8
                     saturation (int)    : min=0 max=15 step=1 default=7 value=7
                            hue (int)    : min=-10 max=10 step=1 default=0value=0
 white_balance_temperature_auto (bool)   : default=1 value=1
                          gamma (int)    : min=1 max=10 step=1 default=7 value=7
                           gain (int)    : min=0 max=0 step=0 default=0 value=0
           power_line_frequency (menu)   : min=0 max=2 default=2 value=2
      white_balance_temperature (int)    : min=2800 max=6500 step=1 default=2800 value=2800 flags=inactive
                      sharpness (int)    : min=0 max=15 step=1 default=6 value=6
         backlight_compensation (int)    : min=0 max=1 step=1 default=0 value=0
                  exposure_auto (menu)   : min=0 max=3 default=3 value=3
              exposure_absolute (int)    : min=4 max=5000 step=1 default=625 value=625 flags=inactive
                 focus_absolute (int)    : min=0 max=21 step=1 default=16 value=16 flags=inactive
                     focus_auto (bool)   : default=1 value=1

然后我使用此命令以特定分辨率将/dev/video0 输出到左侧的/dev/video90:

ffmpeg -loglevel verbose -y \
  -f v4l2 -thread_queue_size 512 -i /dev/video0 \
  -filter_complex "nullsrc=size=960x240 [base]; \
          [0:v] format=pix_fmts=yuva420p, setpts=PTS-STARTPTS, scale=320x240 [left]; \
          [base][left] overlay=shortest=1" \
  -f v4l2 /dev/video90

这会导致以下错误:

[v4l2 @ 0x55fa67d02f60] Unknown V4L2 pixel format equivalent for yuva420p
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:0 --
Conversion failed!

完整日志:

ffmpeg version 3.4.4-1~16.04.york0 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  configuration: --prefix=/usr --extra-version='1~16.04.york0' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  WARNING: library configuration mismatch
  avcodec     configuration: --prefix=/usr --extra-version='1~16.04.york0'--toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared --enable-version3 --disable-doc --disable-programs --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libtesseract --enable-libvo_amrwbenc
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
[video4linux2,v4l2 @ 0x55fa67cfca00] fd:5 capabilities:84200001
[video4linux2,v4l2 @ 0x55fa67cfca00] Querying the device for the current frame size
[video4linux2,v4l2 @ 0x55fa67cfca00] Setting frame size to 640x480
Input #0, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 273229.829138, bitrate: 147456 kb/s
    Stream #0:0: Video: rawvideo, 1 reference frame (YUY2 / 0x32595559), yuyv422, 640x480, 147456 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
[Parsed_nullsrc_0 @ 0x55fa67d00680] size:960x240 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_scale_3 @ 0x55fa67d02240] w:320 h:240 flags:'bilinear' interl:0
Stream mapping:
  Stream #0:0 (rawvideo) -> format
  overlay -> Stream #0:0 (rawvideo)
Press [q] to stop, [?] for help
[Parsed_nullsrc_0 @ 0x55fa67cfc760] size:960x240 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_scale_3 @ 0x55fa67d055c0] w:320 h:240 flags:'bilinear' interl:0
[graph 0 input from stream 0:0 @ 0x55fa67d06a40] w:640 h:480 pixfmt:yuyv422 tb:1/1000000 fr:30/1 sar:0/1 sws_param:flags=2
[auto_scaler_0 @ 0x55fa67d05d80] w:iw h:ih flags:'bilinear' interl:0
[Parsed_format_1 @ 0x55fa67d04360] auto-inserting filter 'auto_scaler_0' between the filter 'graph 0 input from stream 0:0' and the filter 'Parsed_format_1'
[auto_scaler_0 @ 0x55fa67d05d80] w:640 h:480 fmt:yuyv422 sar:0/1 -> w:640 h:480 fmt:yuva420p sar:0/1 flags:0x2
[Parsed_format_1 @ 0x55fa67d04360] TB:0.000001 FRAME_RATE:30.000000 SAMPLE_RATE:nan
[Parsed_scale_3 @ 0x55fa67d055c0] w:640 h:480 fmt:yuva420p sar:0/1 -> w:320 h:240 fmt:yuva420p sar:0/1 flags:0x2
[Parsed_overlay_4 @ 0x55fa67d05e80] main w:960 h:240 fmt:yuva420p overlay w:320 h:240 fmt:yuva420p
[Parsed_overlay_4 @ 0x55fa67d05e80] [framesync @ 0x55fa67d05fa8] Selected 1/1000000 time base
[Parsed_overlay_4 @ 0x55fa67d05e80] [framesync @ 0x55fa67d05fa8] Sync level 2
[v4l2 @ 0x55fa67d02f60] Unknown V4L2 pixel format equivalent for yuva420p
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:0 --
Conversion failed!

我试过但没有奏效:

使用 -f h264 作为输出，以 av_interleaved_write_frame(): Invalid argument 错误结束

Answer 1

由于您的叠加输入具有 alpha，因此叠加过滤器从 nullsrc 过滤器请求 alpha 格式。现在，v4l2 输出设备不接受带有 alpha 的 YUV 格式和 与大多数编码器不同，它不能与过滤器自动协商，因此会显示错误。在覆盖之后强制使用支持的格式以避免这种情况。

利用

ffmpeg -loglevel verbose -y \
  -f v4l2 -thread_queue_size 512 -i /dev/video0 \
  -filter_complex "nullsrc=size=960x240, format=yuv420p [base]; \
          [0:v] format=pix_fmts=yuva420p, setpts=PTS-STARTPTS, scale=320x240 [left]; \
          [base][left] overlay=shortest=1,format=yuv420p" \
  -f v4l2 /dev/video90