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• using Qt's QProcess as popen (with ffmpeg rawvideo)

  9 octobre 2019, par Alex

  I inserted some code in a video application to export using ffmpeg
  with stdin (rawideo rgba format), to quickly test that it worked I
  used popen(), the tests went well and since the application is
  written using Qt I thought of modify the patch using QProcess and
  ->write().

  The application shows no errors and works properly but the generated
  video files are not playable neither with vlc nor with mplayer while
  those generated with popen() work perfectly with both. I have the
  feeling that ->close() or ->terminate() does not properly close
  ffmpeg and consequently the file, but I don’t know how to verify it
  nor I found alternative ways to end the executed command, beside
  ->waitForBytesWritten() should wait for the data to be written,
  suggestions ? Am I doing something wrong ?

  (Obviously I can’t prepare a testable example it would take me more
  time than the patch took)

  Below is the code I entered, in the case #else the Qt code

  Initialization

  #if defined(EXPORT_POPEN) && EXPORT_POPEN == 1
  
        pipe_frame.file = popen("/tmp/ffmpeg-rawpipe.sh", "w");
  
        if (pipe_frame.file == NULL) {
  
          return false;
  
        }
  
  #else
  
        pipe_frame.qproc = new QProcess;
  
        pipe_frame.qproc->start("/tmp/ffmpeg-rawpipe.sh", QIODevice::WriteOnly);
  
        if(!pipe_frame.qproc->waitForStarted()) {
  
          return false;
  
        }
  
  #endif

  Writing a frame

  #if defined(EXPORT_POPEN) && EXPORT_POPEN == 1
  
            fwrite(pipe_frame.data, pipe_frame.width*4*pipe_frame.height , 1, pipe_frame.file);
  
  #else
  
            qint64 towrite = pipe_frame.width*4*pipe_frame.height,
  
              written = 0, partial;
  
            while(written < towrite) {
  
              partial = pipe_frame.qproc->write(&pipe_frame.data[written], towrite-written);
  
              pipe_frame.qproc->waitForBytesWritten(-1);
  
              written += partial;
  
            }
  
  #endif

  Termination

  #if defined(EXPORT_POPEN) && EXPORT_POPEN == 1
  
        pclose(pipe_frame.file);
  
  #else
  
        pipe_frame.qproc->terminate();
  
        //pipe_frame.qproc->close();
  
  #endif

  edit

  ffmpeg-rawpipe.sh

  #!/bin/sh
  
  exec ffmpeg-cuda -y -f rawvideo -s 1920x1080 -pix_fmt rgba -r 25 -i - -an -c:v h264_nvenc \
  
          -cq:v 19 \
  
          -profile:v high /tmp/test.mp4

  I made some changes, I added the unbuffered flag to the open

  pipe_frame.qproc->start("/tmp/ffmpeg-rawpipe.sh", QIODevice::WriteOnly|QIODevice::Unbuffered);

  And therefore simplified the write

  qint64 towrite = pipe_frame.width*4*pipe_frame.height;
  
  pipe_frame.qproc->write(pipe_frame.data, towrite);
  
  pipe_frame.qproc->waitForBytesWritten(-1);

  I added a closeWriteChannel before closing the application (hoping that stopping the stdin ffmpeg pipe ends properly, just in case, I’m not sure it doesn’t)

  pipe_frame.qproc->waitForBytesWritten(-1);
  
  pipe_frame.qproc->closeWriteChannel();
  
  //pipe_frame.qproc->terminate();
  
  pipe_frame.qproc->close();

  But nothing changes, the mp4 file is created and contains data but from the mplayer log I see that it is misinterpreted, the video format is not recognized and it looks for an audio that is not there.

• avformat/matroskaenc : Remove unnecessary avio_tell(), avio_seek()

  22 janvier 2020, par Andreas Rheinhardt

  avformat/matroskaenc : Remove unnecessary avio_tell(), avio_seek()
  avio_close_dyn_buf() has a bug : When the write pointer does not point to
  
  the end of the written data when calling it (i.e. when one has performed
  
  a seek back to update already written data), it would not add padding to
  
  the end of the buffer, but to the current position, overwriting other
  
  data ; furthermore the reported size would be wrong (off by the amount of
  
  data it has overwritten with padding).
  In order not to run into this when updating already written elements or
  
  elements for which size has only been reserved, the Matroska muxer would
  
  first record the current position of the dynamic buffer, then seek to
  
  the desired position, perform the update and seek back to the earlier
  
  position.
  But now that end_ebml_master_crc32() does not make use of
  
  avio_close_dyn_buf() any more, this is no longer necessary.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• what is a steps to apply filter to video using ffmpeg c program android ndk

  13 juillet 2016, par Rajkumar

  I am newbie to ffmpeg with android. i have an input video birds.mp4 that have following settings

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'birds.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf54.59.106
  
    Duration: 00:00:21.60, start: 0.000000, bitrate: 574 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 320x176 [
  
  SAR 44:45 DAR 16:9], 440 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, flt
  
  p, 127 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler

  i have compiled ffmpeg as *.so file for android. And i write a Jni wrapper. Now i want to apply a filter to that input video and save it to output.mp4 with same setting as shown. i know basic terminologies encoding, decoding, muxing, transcoding.
  I want to know How to do this task ? and What are the techniques involved to do this task ?

  I use ffmpeg-3.1 c-source code grabbed from github. i refer this sample it doesn’t guide me.

  If anybody experienced this problem please guide me right direction.