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• How to save image from the middle of a video ?

  29 octobre 2017, par puppon -su

  I need to make a thumbnail for a video, to seek to the 25% of a video and save the image. Here is what I’m doing right now, but it only saves black image.

  #include 
  
  
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavutil></libavutil>dict.h>
  
  
  
  int main (int argc, char **argv)
  
  {
  
  
  
      av_register_all();
  
  
  
      AVFormatContext *pFormatCtx = avformat_alloc_context();
  
  
  
      int res;
  
  
  
      res = avformat_open_input(&amp;pFormatCtx, "test.mp4", NULL, NULL);
  
      if (res) {
  
          return res;
  
      }
  
  
  
  
  
      avformat_find_stream_info(pFormatCtx, NULL);
  
  
  
      int64_t duration = pFormatCtx->duration;
  
  
  
  
  
      // Find the first video stream
  
      int videoStream=-1;
  
      for(int i=0; inb_streams; i++) {
  
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
  
              videoStream=i;
  
              break;
  
          }
  
      }
  
      if(videoStream==-1) {
  
          return -1;
  
      }
  
  
  
      AVCodecContext *pCodecCtxOrig = NULL;
  
  
  
      // Get a pointer to the codec context for the video stream
  
      pCodecCtxOrig=pFormatCtx->streams[videoStream]->codec;
  
  
  
  
  
      AVCodec *pCodec = NULL;
  
      // Find the decoder for the video stream
  
      pCodec=avcodec_find_decoder(pCodecCtxOrig->codec_id);
  
      if(pCodec==NULL) {
  
          fprintf(stderr, "Unsupported codec!\n");
  
          return -1; // Codec not found
  
      }
  
  
  
  
  
      AVCodecContext *pCodecCtx = NULL;
  
      // Copy context
  
      pCodecCtx = avcodec_alloc_context3(pCodec);
  
      if(avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0) {
  
          fprintf(stderr, "Couldn't copy codec context");
  
          return -1; // Error copying codec context
  
      }
  
  
  
  
  
      // Open codec
  
      if(avcodec_open2(pCodecCtx, pCodec, NULL)&lt;0) {
  
          return -1; // Could not open codec
  
      }
  
  
  
  
  
      AVFrame *pFrame = NULL;
  
  
  
      pFrame=av_frame_alloc();
  
  
  
      AVFrame *pFrameRGB = NULL;
  
  
  
      pFrameRGB=av_frame_alloc();
  
  
  
  
  
  
  
      // Determine required buffer size and allocate buffer
  
      int numBytes=avpicture_get_size(AV_PIX_FMT_RGB24, pCodecCtx->width,
  
                                  pCodecCtx->height);
  
  
  
      uint8_t *buffer = NULL;
  
      buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
  
  
      // Assign appropriate parts of buffer to image planes in pFrameRGB
  
      // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
  
      // of AVPicture
  
      res = avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_RGB24,
  
                      pCodecCtx->width, pCodecCtx->height);
  
      if (res&lt;0) {
  
          return;
  
      }
  
  
  
  
  
  
  
      // I've set this number randomly
  
      res = av_seek_frame(pFormatCtx, videoStream, 20.0, AVSEEK_FLAG_FRAME);
  
      if (res&lt;0) {
  
          return;
  
      }
  
  
  
  
  
  
  
      AVPacket packet;
  
      while(1) {
  
          av_read_frame(pFormatCtx, &amp;packet);
  
          if(packet.stream_index==videoStream) {
  
              int frameFinished;
  
              avcodec_decode_video2(pCodecCtx, pFrame, &amp;frameFinished, &amp;packet);
  
              if(frameFinished) {
  
                  SaveFrame(pFrameRGB, pCodecCtx->width,
  
                      pCodecCtx->height);
  
                  break;
  
              }
  
  
  
          }
  
      }
  
  
  
  
  
      avformat_close_input(&amp;pFormatCtx);
  
      return 0;
  
  }
  
  
  
  
  
  
  
  void SaveFrame(AVFrame *pFrame, int width, int height) {
  
    FILE *pFile;
  
    char szFilename[] = "frame.ppm";
  
    int  y;
  
  
  
    // Open file
  
    pFile=fopen(szFilename, "wb");
  
    if(pFile==NULL)
  
      return;
  
  
  
    // Write header
  
    fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  
  
    // Write pixel data
  
    for(y=0; ydata[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  
  
    // Close file
  
    fclose(pFile);
  
  }

  I was following this tutorial http://dranger.com/ffmpeg/tutorial01.html http://dranger.com/ffmpeg/tutorial07.html . It says that it was updated in 2015, but there already are some warnings about deprecated code, for example here : pFormatCtx->streams[i]->codec.

  I got video duration (in microseconds), but I don’t understand what I should send to av_seek_frame. Can I somehow use frame number for both duration and seeking, instead of time ?

• FFmpeg - What muxer do i need to save an AAC audio stream

  3 août 2022, par David Barishev

  I'm developing Android application, and im using ffmpeg for conversion of files.
  
I want my binary file to be as slim as possible since i don't have many input formats and output formats, and my operation is quite basic.And of course not to bloat the APK.

  



  In my program ffmpeg receives a file, and copys the audio stream (-acodec copy), the audio stream will always be aac (mp4a). What i need is to save the stream to file.
  
My command looks like this : ffmpeg -i {Input} -vn -acodec copy output.aac.

  



  What muxer do i need to for muxing aac to file ? I have tried flv,mp3,mov but i always get
  
Unable to find a suitable output format for 'output.aac', so these options are wrong.
  
I don't need an encoder for stream copy btw.

  



  Side note : this command work flawlessly on full installation of ffmpeg , but I don't know which muxer it uses. If there is a way to output the muxer it uses from regular ffmpeg run, it would work too.

  


• Unable to save Matplotlib animations using ffmpeg

  23 décembre 2017, par jtpointon

  I have installed ffmpeg and added it to path, and checked it works in command prompt, but I am still unable to save animations. I have tried creating a sin wave that will animate when I don’t try to save it, but throws an error when I do to demonstrate ;

  from __future__ import division
  
  
  
  import numpy as numpy
  
  from matplotlib import pyplot as pyplot
  
  from matplotlib import animation
  
  
  
  fig = pyplot.figure()
  
  ax = pyplot.axes(xlim=(0, 2), ylim=(-2, 2))
  
  line, = ax.plot([], [], lw=2)
  
  
  
  def init():
  
      line.set_data([], [])
  
      return line,
  
  
  
  def animate(i):
  
      x = numpy.linspace(0, 2, 1000)
  
      y = numpy.sin(2 * numpy.pi * (x - 0.01 * i))
  
      line.set_data(x, y)
  
      return line,
  
  
  
  anim = animation.FuncAnimation(fig, animate, init_func=init, frames=200, 
  
      interval=20, blit=True, repeat=False)
  
  
  
  FFwriter = animation.FFMpegWriter()
  
  anim.save('animation_testing.mp4', writer = FFwriter)
  
  
  
  pyplot.show()

  When I try to run this it throws the same errors over and over again, I assume as it iterates through each frame ;

  Traceback (most recent call last):
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\backends\backend_wx.py", line 212, in _on_timer
  
      TimerBase._on_timer(self)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\backend_bases.py", line 1273, in _on_timer
  
      ret = func(*args, **kwargs)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 910, in _step
  
      still_going = Animation._step(self, *args)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 769, in _step
  
      self._draw_next_frame(framedata, self._blit)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 787, in _draw_next_frame
  
      self._pre_draw(framedata, blit)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 800, in _pre_draw
  
      self._blit_clear(self._drawn_artists, self._blit_cache)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 840, in _blit_clear
  
      a.figure.canvas.restore_region(bg_cache[a])
  
  KeyError: 

  Since it mentioned an error in _blit_clear I tried changing blit to False in FuncAnimation, but then it wouldn’t animate in the pyplot.show() when I didn’t try to save.

  I’m unsure as to where the error could be and so can’t work out how to fix this.

  I’m using Windows 10, python 2.7.6 and matplotlib version 1.4.2

  Many Thanks !