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• how to record camera to file while encoding stream to v4l2-loopback device ?

  3 février 2021, par Jonatas

  So i have this logitech c920 camera 1920x1080 h264 capable and i would like to record the camera to file while at the same time copying/encoding the stream to a loopback device so the camera can be still used by other apps.
here is the code i got so far :

  


  ffmpeg -report -f alsa -i hw:CARD=C920,DEV=0 -r 1500 -s 1920x1080 -f v4l2 -vcodec h264 \
-i /dev/video1 -copyinkf -vcodec copy /home/jonatas/Videos/2021-02-01185658.mp4 \ 
-f v4l2 /dev/video0


  


  error :

  


  Unknown V4L2 pixel format equivalent for yuvj420p
Could not write header for output file #1 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 1:0 -- 


  


  some info on /dev/video0(loopbackdevice) :

  


  v4l2-ctl -d /dev/video0

    Device Caps      : 0x05208003
        Video Capture
        Video Output
        Video Memory-to-Memory
        Read/Write
        Streaming
        Extended Pix Format
Priority: 0
Video input : 0 (loopback: ok)
Video output: 0 (loopback in)
Format Video Output:
    Width/Height      : 1280/720
    Pixel Format      : 'YUYV' (YUYV 4:2:2)
    Field             : None
    Bytes per Line    : 2560
    Size Image        : 1843200
    Colorspace        : sRGB
    Transfer Function : Default (maps to sRGB)
    YCbCr/HSV Encoding: Default (maps to ITU-R 601)
    Quantization      : Default (maps to Limited Range)
    Flags             : 
Streaming Parameters Video Capture:
    Frames per second: 30.000 (30/1)
    Read buffers     : 8
Streaming Parameters Video Output:
    Frames per second: 30.000 (30/1)
    Write buffers    : 8

User Controls

                    keep_format 0x0098f900 (bool)   : default=0 value=0
              sustain_framerate 0x0098f901 (bool)   : default=0 value=0
                        timeout 0x0098f902 (int)    : min=0 max=100000 step=1 default=0 value=0
               timeout_image_io 0x0098f903 (bool)   : default=0 value=0


  


  some info on my camera in /dev/video1

  


  v4l2-ctl -d /dev/video1 --all
Driver Info:
    Driver name      : uvcvideo
    Card type        : HD Pro Webcam C920
    Bus info         : usb-0000:00:14.0-7.2
    Driver version   : 5.4.78
    Capabilities     : 0x84a00001
        Video Capture
        Metadata Capture
        Streaming
        Extended Pix Format
        Device Capabilities
    Device Caps      : 0x04200001
        Video Capture
        Streaming
        Extended Pix Format
Media Driver Info:
    Driver name      : uvcvideo
    Model            : HD Pro Webcam C920
    Serial           : EC6C336F
    Bus info         : usb-0000:00:14.0-7.2
    Media version    : 5.4.78
    Hardware revision: 0x00000011 (17)
    Driver version   : 5.4.78
Interface Info:
    ID               : 0x03000002
    Type             : V4L Video
Entity Info:
    ID               : 0x00000001 (1)
    Name             : HD Pro Webcam C920
    Function         : V4L2 I/O
    Flags         : default
    Pad 0x01000007   : 0: Sink
      Link 0x0200001f: from remote pad 0x100000a of entity 'Processing 3': Data, Enabled, Immutable
Priority: 2
Video input : 0 (Camera 1: ok)
Format Video Capture:
    Width/Height      : 1280/720
    Pixel Format      : 'H264' (H.264)
    Field             : None
    Bytes per Line    : 2560
    Size Image        : 1843200
    Colorspace        : sRGB
    Transfer Function : Default (maps to sRGB)
    YCbCr/HSV Encoding: Default (maps to ITU-R 601)
    Quantization      : Default (maps to Full Range)
    Flags             : 
Crop Capability Video Capture:
    Bounds      : Left 0, Top 0, Width 1280, Height 720
    Default     : Left 0, Top 0, Width 1280, Height 720
    Pixel Aspect: 1/1
Selection Video Capture: crop_default, Left 0, Top 0, Width 1280, Height 720, Flags: 
Selection Video Capture: crop_bounds, Left 0, Top 0, Width 1280, Height 720, Flags: 
Streaming Parameters Video Capture:
    Capabilities     : timeperframe
    Frames per second: 30.000 (30/1)
    Read buffers     : 0
                     brightness 0x00980900 (int)    : min=0 max=255 step=1 default=128 value=128
                       contrast 0x00980901 (int)    : min=0 max=255 step=1 default=128 value=128
                     saturation 0x00980902 (int)    : min=0 max=255 step=1 default=128 value=128
 white_balance_temperature_auto 0x0098090c (bool)   : default=1 value=1
                           gain 0x00980913 (int)    : min=0 max=255 step=1 default=0 value=255
           power_line_frequency 0x00980918 (menu)   : min=0 max=2 default=2 value=2
                0: Disabled
                1: 50 Hz
                2: 60 Hz
      white_balance_temperature 0x0098091a (int)    : min=2000 max=6500 step=1 default=4000 value=3233 flags=inactive
                      sharpness 0x0098091b (int)    : min=0 max=255 step=1 default=128 value=128
         backlight_compensation 0x0098091c (int)    : min=0 max=1 step=1 default=0 value=0
                  exposure_auto 0x009a0901 (menu)   : min=0 max=3 default=3 value=3
                1: Manual Mode
                3: Aperture Priority Mode
              exposure_absolute 0x009a0902 (int)    : min=3 max=2047 step=1 default=250 value=333 flags=inactive
         exposure_auto_priority 0x009a0903 (bool)   : default=0 value=0
                   pan_absolute 0x009a0908 (int)    : min=-36000 max=36000 step=3600 default=0 value=0
                  tilt_absolute 0x009a0909 (int)    : min=-36000 max=36000 step=3600 default=0 value=0
                 focus_absolute 0x009a090a (int)    : min=0 max=250 step=5 default=0 value=0
                     focus_auto 0x009a090c (bool)   : default=1 value=0
                  zoom_absolute 0x009a090d (int)    : min=100 max=500 step=1 default=100 value=100


  


  if i remove the 3rd line of my script the camera records the stream of video and sound to the file flawless. i tried diferent things for the 3rd line as -vcodec and something to do with pix-format flag to YUYV without success.
Is it possible to achieve this with just one ffmpeg process ?
Will the sound be made available to the loopback device also ?
How to transcode it to the proper pixel format used by loopback device ?

  


• multiple GPU encoding use FFMPEG under multiple threads environment

  8 septembre 2022, par shenuo

  Here is the application situation.
I want use 4 NV GPUs to carry out some calculation work (CUDA based), and encoding work (FFMPEG &NVEC), it works fine when they are in serial. But when I want them to be parallel. like this

  


  void encodingwork(){
            #pragma omp parallel for num_threads(4)
                for (int i = 0; i < 4; i++) {
                    cudaSetDevice(i);
                    encodingwork();
                }
        }

        int main(){
            thread thd;
            for (int k = 0; k < N; k++) {
#pragma omp parallel for num_threads(4)
                for (int i = 0; i < 4; i++) {
                    cudaSetDevice(i);
                    cudawork();
                }
                if (k != 0)
                    thd.join();
                thd = thread(encodingwork);
            }
            thd.join();
        }


  


  an error will be thrown out from ffmpeg. just like

  


  [AVHWDeviceContext @ 000002334959ac80] cu->cuMemFree((CUdeviceptr)data) failed -> CUDA_ERROR_ILLEGAL_ADDRESS: an illegal memory access was encountered

[hevc_nvenc @ 00000230c956b200] EncodePicture failed!: generic error (20):
Error sending a frame for encoding: -1313558101 (Unknown error occurred)


  


  can anybody tell me what's wrong with this ?

  


• Encode Ogg/Opus with very specific structure

  28 septembre 2022, par sonovice

  I have an ogg/opus file with a pretty special structure that I would like to reproduce.

  


  opusinfo returns a few hints of how it was made :

  


  New logical stream (#1, serial: 59d24a85): type opus
Encoded with Lavf56.40.101
User comments section follows...
        encoder=Lavc56.60.100 libopus
        encoder_options=--quiet --bitrate 96 --vbr
        pad=00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Opus stream 1:
        Pre-skip: 312
        Playback gain: 0 dB
        Channels: 2
        Original sample rate: 48000Hz
        Packet duration:   60.0ms (max),   56.6ms (avg),   20.0ms (min)
        Page duration:   1460.0ms (max),  323.6ms (avg),  120.0ms (min)
        Total data length: 38872802 bytes (overhead: 1.12%)
        Playback length: 51m:11.473s
        Average bitrate: 101.2 kb/s, w/o overhead: 100.1 kb/s
Logical stream 1 ended


  


  Lavf/Lavc suggests that it was made with FFMPEG, but I am not able to find suitable settings.

  


  Looking at the actual bytes, it starts with an 0x200 (512) byte long ogg page containing metadata, followed by an 0xE00 (3584) byte long ogg page with actual audio content. Both pages sum up exactly to 0x1000 (4096) bytes.


  


  After that, each page is exactly 0x1000 (4096) bytes long with potential zero padding, so that the pages start at offsets 0x1000, 0x2000, 0x3000 etc.


  


  Is there any known tool or library that can produce such ogg/opus files from PCM wave audio ?

  


  (Unfortunately I cannot share the file as it contains proprietary content.)