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• Where i made mistake - FFMPEG (LINUX) PROBLEM - basic

  22 mars 2019, par Fejor

  I just start learing ffmpeg, i have code (like bellow), but it’s doing nothing. Where i make mistake ? What wrong with that ?
  Sory for my language mistakes, i am not realy fluent in english

  fmpeg -i videoplayback.mp4 -filter_complex "[1:v]trim=start=0:end=1,setpts=PTS-STARTPTS,scale=480x360,setsar=sar=16/9[intro1];
  
  [1:v]trim=start=1:end=123.39,setpts=PTS-STARTPTS,scale=480x360,setsar=sar=16/9[main1];
  
  [1:v]trim=start=123.39:end=124.39,setpts=PTS-STARTPTS,scale=480x360,setsar=sar=16/9[end1];
  
  [intro1]format=pix_fmts=yuva420p, fade=t=in:st=0:d=1:alpha=1[intro1];
  
  [end1]format=pix_fmts=yuva420p, fade=t=in:st=0:d=1:alpha=1[end1];
  
  [intro1][main1][end1][output];
  
  [a:1][audio]; -vcodec libx264 -map "[output]" -map"[audio]" "output.mp4"

• {OpenAL(+FFmpeg)} How to queue variable size buffer due to ogg format ?

  11 février 2014, par user3293833

  (First of all, I may feel sorry about my poor English as it's not my native language.)

  I use FFmpeg to decode some audio file and play it with OpenAL by "stream"(i.e."queue" and "unqueue" function of OpenAL).

  When I use my program to play .ogg file, I find that it has a variable nb_samples.(due to ogg has variable bit rate ??) There are 128 B, 512 B and 1024 B of nb_samples. As a results, I must call alDeleteBuffers and alGenBuffers before I use alBufferSamplesSOFT(similar to alBufferData) because it would fail to call alBufferSamplesSOFT without recreate the buffer.
  Notes : alBufferSamplesSOFT is provided by OpenAL Soft. You can just see it as alBufferData.

  Nevertheless, I think it's foolish and inefficient if I do this. Is there is some smart method ? I paste the part of code :

  while (av_read_frame(...) == 0){
  
    avcodec_decode_audio4(...);
  
    swr_convert(...);  // to convert PCM format from FLTP to FLT
  
    alDeleteBuffers(1, theBuffers[?]);
  
    alGenBuffers(1, theBuffers[?]);
  
    alBufferSamplesSOFT(...);  // put those data into OpenAL buffer
  
  }

  if I don't do this, It would failed to update the OpenAL buffer. Is there any method to create a variable size buffer or a big size buffer ? Or is there any method to change the size of buffer ?

  Thanks for you guys.

• Mirror flip video taken from front camera in Android

  5 août 2016, par DAVIDBALAS1

  I have a camera application which is able to capture images and record videos. However, when capturing images or recording videos from the device front facing camera the result is flipped, like you are looking at the mirror. I want to flip it again so it will look normal. I managed to do this with images by flipping the Bitmap using Matrix :

     public Bitmap flip(Bitmap bitmap) {
  
          int w = bitmap.getWidth();
  
          int h = bitmap.getHeight();
  
          Matrix matrix = new Matrix();
  
          float[] mirrorY = {-1, 0, 0, 0, 1, 0, 0, 0, 1};
  
          Matrix matrixMirrorY = new Matrix();
  
          matrixMirrorY.setValues(mirrorY);
  
          matrix.postConcat(matrixMirrorY);
  
          matrix.postRotate(90);
  
          return Bitmap.createBitmap(bitmap, 0, 0, w, h, matrix, true);
  
      }

  I can’t figure out how to flip videos taken by MediaRecorder, I know I can run a ffmpeg command :

  -i /pathtooriginalfile/originalfile.mp4 -vf hflip -c:a copy /pathtosave/flippedfile.mp4

  but I don’t know how to run a ffmpeg command from code and I can’t find a different way. There are a lot of topics discussing this issue but I couldn’t find a solution to work. Notice : It is possible, Snapchat got this to work somehow.

  Thanks.

  P.S Sorry for my English