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• Get MP3 content in C ? ffmpeg or mpg123lib ?

  20 novembre 2014, par Nicolás Múnera

  I’m trying for a personal project of mine to mix two mp3 files into one. I’ve been investigating for a couple of days how to read an mp3 with C and i’ve come up with two libraries, ffmpeg and mpg3lib, unfortunately the documentation is a little bit confusing.

  For now I’m trying to get the content of one MP3 file, I just want to understand which parts are valuable and which parts of the data I get are the ones i’m supposed to mix together. This is what i’ve got so far :

  int cont = 0;
  
  fprintf(stderr, "Starting decode...\n");
  
  while(1)
  
  {
  
           len = fread(buf, sizeof(unsigned char), INBUFF, in);
  
           if(len <= 0)
  
                   break;
  
           inc += len;
  
           ret = mpg123_feed(m, buf, len);
  
  
  
           while(ret != MPG123_ERR && ret != MPG123_NEED_MORE)
  
           {
  
                   ret = mpg123_decode_frame(m, &num, &audio, &bytes);
  
                   if(ret == MPG123_NEW_FORMAT)
  
                   {
  
                       mpg123_getformat(m, &rate, &channels, &enc);
  
                       initwavformat();
  
                       initwav();
  
                       fprintf(stderr, "New format: %li Hz, %i channels, encoding value %i\n", rate, channels, enc);
  
                   }
  
  
  
                   printf("Frame # %d: %s\n",cont,audio);          
  
                   fwrite(audio, sizeof(unsigned char), bytes, out);
  
                   outc += bytes;
  
           }
  
       if(ret == MPG123_ERR){
  
               fprintf(stderr, "Error: %s", mpg123_strerror(m));
  
               break; 
  
       }
  
   cont++;
  
   }

  With this code, I think i’m getting the content of the MP3, but when I print it I just get some weird characters, so I don’t know which strategy i should take.

  Could you guys give me a little bit of advice with this ?

  Thank you !

• Looking to play back non-encoded video upload then export gif from selection point via FFMPEG

  10 novembre 2019, par Christopher Neil

  We’ve been trying to crack this code all week, reaching out to everyone to see if you have any solutions ?

  1. We want the user to upload a video and in the next step he will select a small 5 second loop of the video which will be made as a gif.
  2. Old developer was able to do this by splicing the video at 10 seconds instead of 5 but not re-encoding it meant that it would sometimes be beyond 12 seconds and in some cases less than 7.
  3. We changed the code to force keyframes with re encoding so that it splices the video at exactly 5 seconds to show the loop.
  4. These slices are shown to the user using html5 video player.
  5. Upon selection of the loop that sliced video is converted to gif.

  Everything is working in the vice order. The issue is when the user uploads a large sized and length video this slicing and re-encoding takes forever and that cause the user to feel the site is not working properly.

  What we want is very simple :

  1. Show 5 second portion of the video on loop.
  2. If user wants to select another loop he/she clicks the next button and is taken to the next 5 second loop which would be either at 25% of the video or some other
  3. On selection of that portion it converts it into gif.

• avconv : video from images with multiple names

  15 novembre 2017, par user6760680

  I am trying to do something apparently simple : I would like to make a video from a series of images which have different roots in their filename, with avconv on linux. My images are, say :

  imageA_0001.png
  
  imageA_0002.png
  
  imageA_0003.png
  
  imageB_0001.png
  
  imageB_0002.png
  
  imageB_0003.png
  
  imageB_0004.png

  The question closest to mine that I could fine is this one. Unfortunately, it does not help me, using a command like :

  avconv -pattern_type glob -i 'image?_%04d.png' -c:v libx264 -filter:v "setpts=6.0*PTS" video.mp4

  Note that the first answer therein does not work any more. I tried using multiple -i for each filename, but that does not work either. I would like to be able to do this without renaming files or making links. Isn’t it possible ?