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• Mapping v4l2 pixel format codes to ffmpeg pixel format names

  12 décembre 2019, par DekiChan

  I’m building an app that is capturing frames from any v4l2 supported webcam. I’m controlling the camera with v4l2 (golang package https://github.com/blackjack/webcam) and one of the things I need is pixel format. However, what I get is uint32 representing the format in v4l2.

  I do the streaming by wrapping ffmpeg command and reading from its stdout :

  args := []string{
  
      "-f", "v4l2",
  
      "-c:v", "rawvideo",
  
      "-pix_fmt", pixFmt,
  
      "-s", size,
  
      "-i", input,
  
      "-f", "image2pipe",
  
      "-c:v", "mjpeg",
  
      "-qscale:v", "5",
  
      "-", // pipes to stdout
  
  }
  
  
  
  cmd := exec.Command("ffmpeg", args...)

  Now the problem is that -pix_fmt option requires format name in string that is recognized by ffmpeg (for example 8-bit Bayer RGGB8 corresponds to bayer_rggb8, while this format in v4l2 has code 1111967570).

  I found the mapping code for it in ffmpeg’s libavdevice : https://github.com/FFmpeg/FFmpeg/blob/master/libavdevice/v4l2-common.h includes the functions I need, but somehow I’m not able to include <libavdevice></libavdevice>v4l2-common.h> in CGo (no problems with <libavdevice></libavdevice>avdevice.h>) :

  package conv
  
  
  
  /*
  
      #cgo pkg-config: libavdevice
  
      #include <libavdevice></libavdevice>avdevice.h>
  
      #include <libavdevice></libavdevice>v4l2-common.h>
  
  */
  
  import "C"
  
  
  
  type (
  
  )
  
  
  
  // PixFmtToFF takes v4l2 pixel format code and converts it to a string
  
  // recognized by ffmpeg command
  
  // example: 1111967570 to "bayer_rggb8"
  
  func PixFmtToFF(v4l2code uint32) (string, error) {
  
      // should work something like this, couldn't test
  
      codecID := C.ff_fmt_v4l2codec(v4l2code)
  
      pixFmt := C.ff_fmt_v4l2ff(vfd.pixelformat, codec_id)
  
      return C.av_get_pix_fmt_name(pixFmt)
  
  }

  Build output returns :

  go build \
  
          -mod=vendor \
  
          -o ./bin/camera-api \
  
          ./cmd/camera-api
  
  # kca/internal/camera/conv
  
  internal/camera/conv/convert.go:6:11: fatal error: libavdevice/v4l2-common.h: No such file or directory
  
    #include <libavdevice></libavdevice>v4l2-common.h>
  
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  compilation terminated.
  
  make: *** [Makefile:13: build/camera-api] Error 2
  
  make: *** [builder/camera-api] Error 2

  Output of pkg-config --libs libavdevice is -L/usr/local/lib -lavdevice.

  So, I have two questions :

  1) How could I include v4l2-common.h so I can use the mapping functions ?

  2) Is there a better way ? I need ffmpeg wrapping so we can support wide range of formats for captured frames.

• ffmpeg file read permission denied in application but not in debug

  25 novembre 2019, par Purgitoria

  My application has a function of taking captured images and using an ffmpeg background worker to stitch these into a time lapse video. The GUI has some simple options for video quality and for the source folder and output file. I had an older version of my application written in VB.NET and that worked without issue but i am rewriting in C# as it supports additional capture and filter capability in the image processing but am having real trouble figuring out what is wrong with this function.

  I have tried relocating ffmpeg to different locations just in case it was a permissions issue but that had no effect and i also tried to put the function in a "try" with a message box to output any exceptions but i got different errors that prevented me from compiling the code. When i run the application from within VS 2015 in the debugging tool the function works just fine and it will create a video from a collection of still images and create a log but when i build and install the application it does not work at all and i cannot see what is causing it to fail. In the options for ffmpeg i used the -report to output a log of what happens in the background worker and in debug it creates this log but from the application it does not so i presumed it was not even running ffmpeg and going straight to the completed stage of the function.

  Function startConversion()
  
  
  
      CheckForIllegalCrossThreadCalls = False
  
      Dim quality As Integer = trbQuality.Value
  
      Dim input As String = tbFolderOpen.Text
  
      Dim output As String = tbFolderSave.Text
  
      Dim exepath As String = Application.StartupPath + "\\bin\ffmpeg.exe"
  
      input = input & "\SCAImg_%1d.bmp"
  
      input = Chr(34) & input & Chr(34)
  
      output = Chr(34) & output & Chr(34)
  
  
  
      Dim sr As StreamReader
  
      Dim ffmpegOutput As String
  
  
  
      ' all parameters required to run the process
  
      proc.StartInfo.UseShellExecute = False
  
      proc.StartInfo.CreateNoWindow = True
  
      proc.StartInfo.RedirectStandardError = True
  
      proc.StartInfo.FileName = exepath
  
      proc.StartInfo.Arguments = "-framerate 25 -start_number 0 -pattern_type sequence -framerate 10 -i " & input & " -r 10 -c:v libx264 -preset slow -crf " & quality & " " & output
  
      proc.Start()
  
  
  
      lblInfo.Text = "Conversion in progress... Please wait..."
  
      sr = proc.StandardError 'standard error is used by ffmpeg
  
      btnMakeVideo.Enabled = False
  
      Do
  
          ffmpegOutput = sr.ReadLine
  
          tbProgress.Text = ffmpegOutput
  
      Loop Until proc.HasExited And ffmpegOutput = Nothing Or ffmpegOutput = ""
  
  
  
      tbProgress.Text = "Finished !"
  
      lblInfo.Text = "Completed!"
  
      MsgBox("Completed!", MsgBoxStyle.Exclamation)
  
      btnMakeVideo.Enabled = True
  
      Return 0
  
  
  
  End Function

  I checked the application folder and it does contain a sub folder \bin with the ffmpeg.exe located within the folder so i then used cmd to run an instance of the installed ffmpeg from the application folder and it seemed to be throwing out permissions errors :

  Failed to open report "ffmpeg-20191101-191452.log" : Permission denied Failed to set value ’1’ for option ’report’ : Permission denied Error parsing global options : Permission denied

  This seems then like it is certainly a permissions problem but where i am not sure. I did not run in to this error when using VB.NET so i am wondering where i am going wrong now. I thought perhaps it would just be a write permission in the application folder so i the removed the -report and ran ffmpeg again using cmd from my application folder and it then gave the error

  C :\Users\CEAstro\Pictures\AnytimeCap : Permission denied

  Am i missing something really obvious in my code or is there something more fundamental i have wrong in my setup ?

  I should also add that i tried running ffmpeg via cmd from a copy that was manually placed elsewhere (i used the same file) and that actually created the report but again i got a permission denied when trying to read the input files, considering it was from the user "my pictures" folder which should not have restrictions on read/write access i am at a rael loss.

• ffmpeg : Audio input device not recognized

  8 février 2020, par shrimpwidget

  What is needed for my ffmpeg command to recognize my audio input device ?

  The following reference has not helped resolve my problem : enter link description here

  I want to record me talking (to my Windows laptop) while my screen activity is captured. While I have succeeded in capturing what’s on the screen (by removing all mention of audio from my command), I have been unable to capture audio, as the device I mention is not recognized by ffmpeg. (I routinely use the default laptop for audio input to Audacity...surely there’s some way to use it in this ffmpeg command, too.)

  My audio devices :

  ffmpeg -list_devices true -f dshow -i dummy
  
  
  
      [dshow @ 000000000044a940] DirectShow audio devices
  
      [dshow @ 000000000044a940]  "Microphone Array (IDT High Defi"
  
      [dshow @ 000000000044a940]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Microphone Array (IDT High Defi"
  
      [dshow @ 000000000044a940]  "Dock Mic (IDT High Definition A"
  
      [dshow @ 000000000044a940]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Dock Mic (IDT High Definition A"
  
      [dshow @ 000000000044a940]  "Jack Mic (IDT High Definition A"
  
      [dshow @ 000000000044a940]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Jack Mic (IDT High Definition A"
  
      [dshow @ 000000000044a940]  "Rec. Playback (IDT High Definit"
  
      [dshow @ 000000000044a940]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Rec. Playback (IDT High Definit"

  The full name is found via regedit : Microphone Array (IDT High Definition Audio CODEC)

  Why isn’t the audio input device found ?

  ffmpeg -y -f gdigrab -i desktop -framerate 10 -f dshow -i audio="Microphone Array (IDT High Definition Audio CODEC)" -vcodec libx264 "C:\jed\ffmpeg\_mydata\clip.mp4"
  
  
  
      [gdigrab @ 0000000000498540] Capturing whole desktop as 1366x768x32 at (0,0)
  
      [gdigrab @ 0000000000498540] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
      Input #0, gdigrab, from 'desktop':
  
        Duration: N/A, start: 1575576239.093815, bitrate: 1006131 kb/s
  
          Stream #0:0: Video: bmp, bgra, 1366x768, 1006131 kb/s, 29.97 fps, 1000k tbr, 1000k tbn, 1000k tbc
  
      [dshow @ 000000000049a5e0] Could not find audio only device with name [Microphone Array (IDT High Definition Audio CODEC)] among source devices of type audio.
  
      [dshow @ 000000000049a5e0] Searching for audio device within video devices for Microphone Array (IDT High Definition Audio CODEC)
  
      [dshow @ 000000000049a5e0] Could not find audio only device with name [Microphone Array (IDT High Definition Audio CODEC)] among source devices of type video.
  
      audio=Microphone Array (IDT High Definition Audio CODEC): I/O error