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• Concatenate multiple videos with a black screen interval into one video

  21 mars 2016, par AHC

  I am using ffmpeg to join a bunch of videos together.
  I am using the classic join ffmpeg code :
  

  ffmpeg -f concat -i joinlist.txt -c copy joinedfile.mp4

  but the problem is that the videos are of different formats, encodings, but the same size : all 640x480. I want to join them all and put a black screen video with no sound every other video :

  video1 + black_screen_video + video2 + black_screen_video + video3 ...

  I generated a black screen video of 2 seconds duration using :

  ffmpeg -f lavfi -i color=c=black:s=640x480:d=2 black_screen_video.mp4

  so all of the videos are of the same size : 640x480, and 25 fps but different codecs. The videos have sound, except for the black screen video.
  I can’t do anything manual, because the number of videos are around several hundred. So it has got to be an automatic way to do all this.

  When I joined them together using the above code, the resulting video does not play correctly at all.

  I know that I have to re-encode them, but how to do this to all these videos at once, with one line of code ?

  Update :
  I am already using with success this code to join them together, but only three, if I have more than one hundred, it is time consuming to write down one by one :

  ffmpeg -i vid1.avi -i vid2.avi -i vid3.avi -filter_complex "[0:v:0] [0:a:0] [1:v:0] [1:a:0] [2:v:0] [2:a:0] concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4

  but this is joining only the videos, not looping the black screen video. When I do with black screen, ffmpeg gives me stream matching errors.

• ffmpeg - avcodec_decode_audio3 always returns 0 with aac decoding on android

  26 novembre 2011, par Android007

  I am writing an audio decoder based on ffmpeg for android, where I have to decode aac audio, but because of some reason it always returns 0 bytes decoded.

  Looks like I pass everything right. Can anybody tell me what went wrong in my case.I copied code from ffplay.c.
  What is the reason avcodec_decode_audio3 function always returns zero ?

  Here is the code from ffplay.c :

  AVPacket *pkt_temp = &is->audio_pkt_temp;
  
      AVPacket *pkt = &is->audio_pkt;
  
      AVCodecContext *dec= is->audio_st->codec;
  
      int n, len1, data_size;
  
      double pts;
  
  
  
            data_size = sizeof(is->audio_buf1);
  
          len1 = avcodec_decode_audio3(dec, (int16_t *)is->audio_buf1, &data_size, pkt_temp);
  
          if (len1 < 0) {
  
              pkt_temp->size = 0;
  
              break;
  
          } 
  
  
  
         if (data_size <= 0){
  
                     //This block always gets executed.
  
              continue;
  
      }

• cvCreateFileCapture always returns "NULL"

  4 août 2012, par user1553247

  I am making an iphone-app with Xcode 4.3.3 and OpenCV 2.4

  I used that "cvCreateFileCapture("simtom.mp4")" to get frame from '.mp4' file but unfortunately, cvCreateFileCapture() always returns "NULL".

  What is the problem ?

  Here is my source code.

   CvCapture *m_pMusicVideo;     
  
  
  
   m_pMusicVideo = cvCreateFileCapture("simtom.mp4");