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• Image to MPEG on Linux works, same code on Android = green video

  5 avril 2018, par JScoobyCed

  EDIT
  I have check the execution and found that the error is not (yet) at the swscale point. My current issue is that the JPG image is not found :
  No such file or directory
  when doing the avformat_open_input(&pFormatCtx, imageFileName, NULL, NULL);
  Before you tell me I need to register anything, I can tell I already did (I updated the code below).
  I also added the Android permission to access the external storage (I don’t think it is related to Android since I can already write to the /mnt/sdcard/ where the image is also located)
  END EDIT

  I have been through several tutorials (including the few posted from SO, i.e. http://dranger.com/ffmpeg/, how to compile ffmpeg for Android...,been through dolphin-player source code). Here is what I have :
  . Compiled ffmpeg for android
  . Ran basic tutorials using NDK to create a dummy video on my android device
  . been able to generate a MPEG2 video from images on Ubuntu using a modified version of dummy video code above and a lot of Googling
  . running the new code on Android device gives a green screen video (duration 1 sec whatever the number of frames I encode)

  I saw another post about iPhone in a similar situation that mentioned the ARM processor optimization could be the culprit. I tried a few ldextra-flags (-arch armv7-a and similar) to no success.

  I include at the end the code that loads the image. Is there something different to do on Android than on linux ? Is my ffmpeg build not correct for Android video encoding ?

  void copyFrame(AVCodecContext *destContext, AVFrame* dest,
  
              AVCodecContext *srcContext, AVFrame* source) {
  
  struct SwsContext *swsContext;
  
  swsContext = sws_getContext(srcContext->width, srcContext->height, srcContext->pix_fmt,
  
                  destContext->width, destContext->height, destContext->pix_fmt,
  
                  SWS_FAST_BILINEAR, NULL, NULL, NULL);
  
  sws_scale(swsContext, source->data, source->linesize, 0, srcContext->height, dest->data, dest->linesize);
  
  sws_freeContext(swsContext);
  
  }
  
  
  
  int loadFromFile(const char* imageFileName, AVFrame* realPicture, AVCodecContext* videoContext) {
  
  AVFormatContext *pFormatCtx = NULL;
  
  avcodec_register_all();
  
  av_register_all();
  
  
  
  int ret = avformat_open_input(&pFormatCtx, imageFileName, NULL, NULL);
  
  if (ret != 0) {
  
      // ERROR hapening here
  
      // Can't open image file. Use strerror(AVERROR(ret))) for details
  
      return ERR_CANNOT_OPEN_IMAGE;
  
  }
  
  
  
  AVCodecContext *pCodecCtx;
  
  
  
  pCodecCtx = pFormatCtx->streams[0]->codec;
  
  pCodecCtx->width = W_VIDEO;
  
  pCodecCtx->height = H_VIDEO;
  
  pCodecCtx->pix_fmt = PIX_FMT_YUV420P;
  
  
  
  // Find the decoder for the video stream
  
  AVCodec *pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
  
  if (!pCodec) {
  
      // Codec not found
  
      return ERR_CODEC_NOT_FOUND;
  
  }
  
  
  
  // Open codec
  
  if (avcodec_open(pCodecCtx, pCodec) < 0) {
  
      // Could not open codec
  
      return ERR_CANNOT_OPEN_CODEC;
  
  }
  
  
  
  // 
  
  AVFrame *pFrame;
  
  
  
  pFrame = avcodec_alloc_frame();
  
  
  
  if (!pFrame) {
  
      // Can't allocate memory for AVFrame
  
      return ERR_CANNOT_ALLOC_MEM;
  
  }
  
  
  
  int frameFinished;
  
  int numBytes;
  
  
  
  // Determine required buffer size and allocate buffer
  
  numBytes = avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
  
  uint8_t *buffer = (uint8_t *) av_malloc(numBytes * sizeof (uint8_t));
  
  
  
  avpicture_fill((AVPicture *) pFrame, buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
  
  AVPacket packet;
  
  int res = 0;
  
  while (av_read_frame(pFormatCtx, &packet) >= 0) {
  
      if (packet.stream_index != 0)
  
          continue;
  
  
  
      ret = avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
      if (ret > 0) {
  
          // now, load the useful info into realPicture
  
          copyFrame(videoContext, realPicture, pCodecCtx, pFrame);
  
          // Free the packet that was allocated by av_read_frame
  
          av_free_packet(&packet);
  
          return 0;
  
      } else {
  
          // Error decoding frame. Use strerror(AVERROR(ret))) for details
  
          res = ERR_DECODE_FRAME;
  
      }
  
  }
  
  av_free(pFrame);
  
  
  
  // close codec
  
  avcodec_close(pCodecCtx);
  
  
  
  // Close the image file
  
  av_close_input_file(pFormatCtx);
  
  
  
  return res;
  
  }

  Some ./configure options :
  --extra-cflags="-O3 -fpic -DANDROID -DHAVE_SYS_UIO_H=1 -Dipv6mr_interface=ipv6mr_ifindex -fasm -Wno-psabi -fno-short-enums -fno-strict-aliasing -finline-limit=300 -mfloat-abi=softfp -mfpu=vfp -marm -march=armv7-a -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE"

  --extra-ldflags="-Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog"

  --arch=armv7-a --enable-armv5te --enable-armv6 --enable-armvfp --enable-memalign-hack

• Matplotlib : Live animation works fine but displays a blank plot when being saved

  18 juillet 2017, par Loïc Poncin

  I made a little forest fire animation. My code is at the end of the question.

  Here is some information before I ask my question :

  • No tree : forest[i,j] = 0
  • A tree : forest[i,j] = 1
  • A tree on fire : forest[i,j] = 2

  Basically what happens is that constructforest creates a 2 dimensional array called forest of size n by m with a probability of tree occupancy called p. After that setonfire sets on fire the forest and while the forest can burn spreadfire spread the fire.

  When I run forestfire with the Python prompt or the IPython prompt I get a nice animation but when I go check the video file that I saved I only see a blank plot.

  I did some research, I found many questions about this issue but none of the advice I read was helpful :

  • matplotlib animation produces a blank
  • Matplotlib animation not working in IPython Notebook (blank plot)
  • Animation from matplotlib not working in spyder
  • Spyder Python Animation not working

  Can someone tell me what is going on please ?

  forestfire.py

  from random import random
  
  
  
  import numpy as np
  
  
  
  import matplotlib.pylab as plt
  
  import matplotlib.colors as mcolors
  
  import matplotlib.animation as animation
  
  
  
  
  
  def hazard(p):
  
      r=random()
  
      assert p>=0 and p<=1
  
      return r <= p
  
  
  
  
  
  def constructforest(n,m,p):
  
      forest = np.zeros((n,n))
  
      for i in xrange(n):
  
          for j in xrange(m):
  
              if hazard(p):
  
                  forest[i,j] = 1
  
      return forest
  
  
  
  
  
  def setfire(forest,i,j):
  
      forest[i,j] = 2
  
      return forest
  
  
  
  
  
  def spreadfire(forest):    
  
  
  
      n,m=forest.shape
  
      c = np.copy(forest)
  
  
  
      for i in xrange(n):
  
          for j in xrange(m):
  
  
  
              if c[i,j] == 1:
  
  
  
                  Y, X = xrange(max(0,i-1),min(n,i+2)), xrange(max(0,j-1),min(m,j+2))
  
  
  
                  for y in Y:
  
                      for x in X:
  
  
  
                          if c[y,x] == 2:
  
                              forest[i,j] = 2                        
  
      return forest
  
  
  
  
  
  def canburn(forest):    
  
  
  
      n,m=forest.shape
  
      c = np.copy(forest)
  
  
  
      for i in xrange(n):
  
          for j in xrange(m):
  
  
  
              if c[i,j] == 1:
  
  
  
                  Y, X = xrange(max(0,i-1),min(n,i+2)), xrange(max(0,j-1),min(m,j+2))
  
  
  
                  for y in Y:
  
                      for x in X:
  
  
  
                          if c[y,x] == 2:
  
                              return True                      
  
      return False
  
  
  
  
  
  def forestfire(forest):
  
  
  
      fig, ax = plt.subplots()
  
  
  
      movie = []    
  
  
  
      # Colormap
  
      red, green, blue = [(1,0,0,1)], [(0,1,0,1)], [(0,0,1,1)]   
  
  
  
      colors = np.vstack((blue, green, red))
  
      mycmap = mcolors.LinearSegmentedColormap.from_list('my_colormap', colors)
  
  
  
      # Initialization
  
      k = 0
  
  
  
      forest = spreadfire(forest)
  
  
  
      im = plt.imshow(forest, animated=True, cmap = mycmap, interpolation="none", origin='lower')
  
      movie.append([im])
  
  
  
      # Fire propagation
  
      while canburn(forest):
  
          k += 1
  
          print k
  
  
  
          forest = spreadfire(forest)
  
  
  
          im = plt.imshow(forest, animated=True, cmap = mycmap, interpolation="none", origin='lower')
  
          movie.append([im])
  
  
  
      return animation.ArtistAnimation(fig, movie, blit=True, repeat_delay=100)
  
  
  
  
  
  
  
  ani = forestfire(setfire(constructforest(101,101,0.4),50,50))
  
  
  
  ani.save("forestfire_test.mp4", writer = 'ffmpeg', fps=5, dpi=500)

  EDIT

  As requested by @Y.Luo by @ImportanceOfBeingErnest in the comments I downgraded matplotlib to 2.0.0 and I changed the framerate of the animation but forestfire_test.mp4 still displays a blank plot.

  Here are my settings :
  
  

• FFmpeg / python - command works when run from shell but fails when run from python

  4 avril 2019, par artembus

  I have a python script which should run an ffmpeg command with this function :

  def transcode(in_path, out_path):
  
      cmd = ["ffmpeg", "-y", "-i", in_path, '-vf smartblur=lr=1']
  
      cmd += ["-an", out_path]
  
      print("Running:", " ".join(cmd))
  
      subprocess.run(cmd, stdout=cmdout, stderr=cmdout)

  When I run the python script it fails with this ffmpeg error :

  Running: ffmpeg -y -i raid/orig/scenes/train/5786088.mp4 -vf smartblur=lr=1 -an raid/4K/scenes/train/5786088.mp4
  
  ffmpeg version 2.8.15-0ubuntu0.16.04.1 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  
    configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv
  
    libavutil      54. 31.100 / 54. 31.100
  
    libavcodec     56. 60.100 / 56. 60.100
  
    libavformat    56. 40.101 / 56. 40.101
  
    libavdevice    56.  4.100 / 56.  4.100
  
    libavfilter     5. 40.101 /  5. 40.101
  
    libavresample   2.  1.  0 /  2.  1.  0
  
    libswscale      3.  1.101 /  3.  1.101
  
    libswresample   1.  2.101 /  1.  2.101
  
    libpostproc    53.  3.100 / 53.  3.100
  
  Unrecognized option 'vf smartblur=lr=1'.
  
  Error splitting the argument list: Option not found

  You can see the command it tries to execute in the first line, when I run it in the command line it works fine. When I run the command in the shell it outputs the same version and parameters of the ffmpeg as written in the error above.

  I feel like I missed something simple yet crucial, anyone can point me to the right direction ?