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• fileapi::WriteFile() doesn't send an input, if processthreadsapi::STARTUPINFO::hStdError is set (ffmpeg)

  23 avril 2021, par Lidekys

  I'm trying to capture my screen using ffmpeg in a different thread (which I create using processthreadsapi::CreateProcess()) so I'd be able to do something else in the main thread, and redirect ffmpeg output, so it wouldn't pop up in the console for the user to see. To stop filming, I send a 'q' input using WriteFile(), and after that I want to save ffmpeg accumulated output using ReadFile().

  


  However, if I set STARTUPINFO::hStdError (note, that ffmpeg output goes to stderr) to a pipe, from which I could read the accumulated data, the inputs I send using WriteFile() are no longer registered and ffmpeg.exe keeps running.

  


  I've tried redirecting ffmpeg output in a simple command line, but I can still stop the process by pressing the q button.

  


  Also, if I record for less than 8 seconds, the input is registered and ffmpeg.exe closes.

  


  Is there something wrong with my code, or is it processthreadsapi issue, any hints will be kindly appreciared !

  


  Here's a minimal code of how I am trying to do it :

  


  &#xA;#include <iostream>&#xA;&#xA;#include &#xA;#include &#xA;&#xA;using namespace std;&#xA;&#xA;HANDLE g_hChildStd_IN_Rd = NULL;&#xA;HANDLE g_hChildStd_IN_Wr = NULL;&#xA;HANDLE g_hChildStd_OUT_Rd = NULL;&#xA;HANDLE g_hChildStd_OUT_Wr = NULL;&#xA;&#xA;int main()&#xA;{&#xA;    //Create IN and OUT pipes&#xA;    SECURITY_ATTRIBUTES saAttr;&#xA;    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);&#xA;    saAttr.lpSecurityDescriptor = NULL;&#xA;&#xA;&#xA;    if (! CreatePipe(&amp;g_hChildStd_OUT_Rd, &amp;g_hChildStd_OUT_Wr, &amp;saAttr, 0) )&#xA;        cout&lt;&lt;"StdoutRd CreatePipe error"&lt;/Start recording&#xA;   if(!CreateProcess(NULL,&#xA;      "ffmpeg -y -f gdigrab -framerate 2 -i desktop record.avi",     // command line&#xA;      NULL,          // process security attributes&#xA;      NULL,          // primary thread security attributes&#xA;      TRUE,          // handles are inherited&#xA;      0,             // creation flags&#xA;      NULL,          // use parent&#x27;s environment&#xA;      NULL,          // use parent&#x27;s current directory&#xA;      &amp;siStartInfo,  // STARTUPINFO pointer&#xA;      &amp;piProcInfo))  // receives PROCESS_INFORMATION&#xA;   {&#xA;    cout&lt;&lt;"Error create process"&lt;/Record for a while&#xA;    while(getch() != &#x27;k&#x27;){&#xA;        cout&lt;&lt;"While press k"&lt;/Stop recording by emulating a Q button push&#xA;    DWORD dwWritten;&#xA;    CHAR chBufW[1] = {&#x27;q&#x27;};&#xA;&#xA;    if ( ! WriteFile(g_hChildStd_IN_Wr, chBufW, 1, &amp;dwWritten, NULL) )&#xA;        cout&lt;&lt;"Error write file"&lt;/Save stdError (ffmpeg) data&#xA;    DWORD dwRead;&#xA;    char stdErrorData[4096];&#xA;    bool bSuccess;&#xA;&#xA;    bSuccess = ReadFile( g_hChildStd_OUT_Wr, stdErrorData, 4096, &amp;dwRead, NULL);&#xA;&#xA;    if(!bSuccess || dwRead == 0)&#xA;        cout&lt;&lt;"Read failed"&lt;code></iostream>

  


• Puzzled with file descriptor in Bash (ffmpeg video capture)

  3 mai 2020, par ChrisAga

  I am trying to use file descriptors in Bash and found a problem I cannot solve.
I have to read a video stream coming from the standard output of a command executed in a coproc. This piece of code works as expected :

  



  ffmpeg \
    -i <(exec cat <&${COPROC[0]}) \
    -c:v $ENCODE_VIDEO_FORMAT_LOSSLESS $ENCODE_VIDEO_OPTIONS_LOSSLESS \
    -c:a copy \
    -progress /dev/fd/1 \
    "${capfile}"


  



  But the cat process is not really useful since ffmpeg -i pipe:<file descriptor="descriptor"></file> seems to do the same. So I tried the following code which fails with pipe:63: Bad file descriptor
 error.

  



  ffmpeg \
    -i pipe:"${COPROC[0]}" \
    -c:v $ENCODE_VIDEO_FORMAT_LOSSLESS $ENCODE_VIDEO_OPTIONS_LOSSLESS \
    -c:a copy \
    -progress /dev/fd/1 \
    "${capfile}"


  



  The actual script is something a bit complicated but here is a minimal testing code for this issue :

  



  #!/bin/bash
#

ENCODE_VIDEO_FORMAT_LOSSLESS=ffv1
ENCODE_VIDEO_OPTIONS_LOSSLESS="-level 3 -threads 7 -coder 1 -context 1 -g 1 -slices 30 -slicecrc 1"

capfile=capure.mkv

coproc ffmpeg  -i file:'Camomille.mkv' -c:v copy -c:a copy -f matroska pipe:1

capture_fd=${COPROC[0]}
echo "hk_capture_pid=${COPROC_PID}"

ffmpeg \
    -i pipe:${COPROC[0]} \
    -c:v $ENCODE_VIDEO_FORMAT_LOSSLESS $ENCODE_VIDEO_OPTIONS_LOSSLESS \
    -c:a copy \
    -progress /dev/fd/1 \
    "${capfile}"


  



  This is the output of the second ffmpeg command :

  



  ffmpeg version 4.1.4-1build2 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.2.1-4ubuntu1)
  configuration: --prefix=/usr --extra-version=1build2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
pipe:63: Bad file descriptor
av_interleaved_write_frame(): Broken pipe                                                                                       
Error writing trailer of pipe:1: Broken pipe                                                                                    
frame=    4 fps=0.0 q=-1.0 Lsize=      48kB time=00:00:00.03 bitrate=10051.1kbits/s speed=3.44x    
video:86kB audio:1kB subtitle:0kB other streams:0kB global headers:2kB muxing overhead: unknown
Conversion failed!


  



  This one fails and if you replace -i pipe:${COPROC[0]} by -i <(exec cat <&${COPROC[0]}) a capture.mkv file is created.

  



  I run ubuntu eoan and bash version is : GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu). I upgraded several times since I started with this issue, so it wouldn't be related too much to bash and ffmpeg versions.

  



  If someone can point me to what I do wrong with bash file descriptors I would be grateful.

  


• Streaming H.264 over UDP using FFmpeg, and "dimensions not set" error

  3 septembre 2015, par Baris Demiray

  I’m trying to stream H.264 over UDP with no luck so far. Here is a minimal code that you can reproduce the problem.

  To compile,

  g++ -o test -lavcodec -lavformat -lavutil test.cpp

  Extra information, I start ffplay as follows. Currently it’s of no use.

  ffplay -i udp://127.0.0.1:8554/live.sdp

  Output of my code (see avio_open() call),

  [libx264 @ 0x6a26c0] using mv_range_thread = 24
  
  [libx264 @ 0x6a26c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.1 Cache64
  
  [libx264 @ 0x6a26c0] profile High, level 3.1
  
  Output #0, h264, to 'udp://127.0.0.1:8554/live.sdp':
  
      Stream #0:0, 0, 0/0: Video: h264 (libx264), -1 reference frame, none, q=-1--1
  
  [h264 @ 0x6a2020] dimensions not set
  
  Cannot write header to stream: Success

  And the code,

  extern "C" {
  
      #include <libavcodec></libavcodec>avcodec.h>
  
      #include <libavformat></libavformat>avformat.h>
  
      #include <libavutil></libavutil>avutil.h>
  
  }
  
  
  
  #include <iostream>
  
  using namespace std;
  
  
  
  int main() {
  
      AVCodecContext* m_codecContext;
  
      AVCodec* m_codec;
  
      AVFormatContext* m_formatContext;
  
      AVStream* m_stream;
  
  
  
      unsigned m_outWidth = 768;
  
      unsigned m_outHeight = 608;
  
  
  
      av_register_all();
  
      avcodec_register_all();
  
      avformat_network_init();
  
  
  
      int errorStatus = 0;
  
      char errorLog[128] = { 0 };
  
      av_log_set_level(AV_LOG_TRACE);
  
  
  
      string m_output("udp://127.0.0.1:8554/live.sdp");
  
  
  
      if (avformat_alloc_output_context2(&amp;m_formatContext, NULL, "h264", m_output.c_str()) &lt; 0) {
  
          cerr &lt;&lt; "Cannot allocate output context: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      AVOutputFormat *m_outputFormat = m_formatContext->oformat;
  
  
  
      m_codec = avcodec_find_encoder(AV_CODEC_ID_H264);
  
      if (!m_codec) {
  
          cerr &lt;&lt; "Cannot find an encoder: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      m_codecContext = avcodec_alloc_context3(m_codec);
  
      if (!m_codecContext) {
  
          cerr &lt;&lt; "Cannot allocate a codec context: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      m_codecContext->pix_fmt = AV_PIX_FMT_YUV420P;
  
      m_codecContext->width = m_outWidth;
  
      m_codecContext->height = m_outHeight;
  
  
  
      if (avcodec_open2(m_codecContext, m_codec, NULL) &lt; 0) {
  
          cerr &lt;&lt; "Cannot open codec: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      m_stream = avformat_new_stream(m_formatContext, m_codec);
  
      if (!m_stream) {
  
          cerr &lt;&lt; "Cannot create a new stream: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      av_dump_format(m_formatContext, 0, m_output.c_str(), 1);
  
  
  
      if ((errorStatus = avio_open(&amp;m_formatContext->pb, m_output.c_str(), AVIO_FLAG_WRITE)) &lt; 0) {
  
          cerr &lt;&lt; "Cannot open output: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      if (avformat_write_header(m_formatContext, NULL) &lt; 0) {
  
          cerr &lt;&lt; "Cannot write header to stream: "
  
               &lt;&lt; av_make_error_string(errorLog, 128, errorStatus) &lt;&lt; endl;
  
          return -1;
  
      }
  
  
  
      cout &lt;&lt; "All done." &lt;&lt; endl;
  
  
  
      return 0;
  
  }
  
  </iostream>

  For those who has even more time to spare on my problem, when I change m_output to rtsp://127.0.0.1:8554/live.sdp, and ffplay command to ffplay -rtsp_flags listen -i rtsp://127.0.0.1:8554/live.sdp I get the error,

  [libx264 @ 0x1e056c0] using mv_range_thread = 24
  
  [libx264 @ 0x1e056c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.1 Cache64
  
  [libx264 @ 0x1e056c0] profile High, level 3.1
  
  Output #0, h264, to 'rtsp://127.0.0.1:8554/live.sdp':
  
      Stream #0:0, 0, 0/0: Video: h264 (libx264), -1 reference frame, none, q=-1--1
  
  Cannot open output: Protocol not found

  Am I naive to expect that streaming protocol will be changed like this ?