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• fastest way to convert any audio file to low bitrate ? [migrated]

  16 février 2013, par kain

  using ffmpeg I'd like to have some directions/parameters to :

  • encode any audio file to a poor bitrate
  • strip artwork from file
  • optimize for speed
  • optimize for size

  My goal is to have a bare-bone file encoded in mp3 in the fastest time possible, quality does not matter (even 96kbps or less), it just needs to be extremely fast and result in small size.

  Any preset to share ?

• Video encoding libraries for iOS

  7 novembre 2011, par peetonn

  I really stucked with that problem, because I haven't seen enough information in the internet regarding video encoding in iOS, however we can observe plenty of apps that deal with the problem of video streaming successfully (skype, qik, justin.tv, etc.)
  I'm going to develop an application, that should send video frames obtained from camera and encoded in h.263 (h.264 or MPEG-4 it is under decision) to a web-server. For this, I need some video encoding library. Obviously, ffmpeg can deal with that task, but it is under LGPL license, which could probably lead to some problems in submitting the app in the AppStore. On the other hand, there are some applications, which are seemed to use ffmpeg library, but only Timelapser clearly states this fact in app description. Does this mean, that other apps are not using ffmpeg or just hiding this information ?

  Please, share your thoughts and experience in this topic. I'm open for dicsussion.

• converting images to mp4 using ffmpeg on iphone

  29 novembre 2011, par user633901

  Up till now, i can create mpeg1 but with no luck for mp4.Maybe we can talk and share information.Someone told me that i have to set some flags for using mp4.But i am stuck at using it...

  following is the working code :

  av_register_all();
  
  printf("Video encoding\n"); 
  
  
  
  /// find the mpeg video encoder 
  
  //codec=avcodec_find_encoder(CODEC_ID_MPEG1VIDEO); 
  
  codec = avcodec_find_encoder(CODEC_ID_MPEG4); 
  
  
  
  if (!codec) { 
  
      fprintf(stderr, "codec not found\n"); 
  
      exit(1); 
  
  } 
  
  
  
  c = avcodec_alloc_context(); 
  
  picture = avcodec_alloc_frame(); 
  
  
  
  // put sample parameters 
  
  c->bit_rate = 400000;
  
  /// resolution must be a multiple of two 
  
  c->width = 240; 
  
  c->height = 320; 
  
  //c->codec_id = fmt->video_codec;
  
  //frames per second 
  
  c->time_base= (AVRational){1,25}; 
  
  c->gop_size = 10; /// emit one intra frame every ten frames 
  
  c->max_b_frames=1; 
  
  c->pix_fmt =PIX_FMT_YUV420P; // PIX_FMT_YUV420P
  
  
  
  if (avcodec_open(c, codec) < 0) { 
  
      fprintf(stderr, "could not open codec\n"); 
  
      exit(1); 
  
  }
  
  
  
  f = fopen([[NSHomeDirectory() stringByAppendingPathComponent:@"test.mp4"] UTF8String], "wb"); 
  
  
  
  if (!f) { 
  
      fprintf(stderr, "could not open %s\n",[@"test.mp4" UTF8String]); 
  
      exit(1); 
  
  } 
  
  
  
  // alloc image and output buffer 
  
  outbuf_size = 100000; 
  
  outbuf = malloc(outbuf_size); 
  
  size = c->width * c->height; 
  
  
  
  #pragma mark - 
  
  
  
  AVFrame* outpic = avcodec_alloc_frame(); 
  
  int nbytes = avpicture_get_size(PIX_FMT_YUV420P, c->width, c->height); //this is half size of numbytes. 
  
  
  
  //create buffer for the output image 
  
  uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes); 
  
  
  
  #pragma mark -  
  
  for(k=0;k<1;k++) { 
  
      for(i=0;i<25;i++) { 
  
          fflush(stdout); 
  
  
  
          int numBytes = avpicture_get_size(PIX_FMT_RGBA, c->width, c->height); 
  
          uint8_t *buffer = (uint8_t *)av_malloc(numBytes*sizeof(uint8_t)); 
  
  
  
          UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"%d.png", i+1]]; 
  
          CGImageRef newCgImage = [image CGImage]; 
  
  
  
          CGDataProviderRef dataProvider = CGImageGetDataProvider(newCgImage); 
  
          CFDataRef bitmapData = CGDataProviderCopyData(dataProvider); 
  
          buffer = (uint8_t *)CFDataGetBytePtr(bitmapData);   
  
          /////////////////////////// 
  
          //outbuffer=(uint8_t *)CFDataGetBytePtr(bitmapData); 
  
          ////////////////////////// 
  
          avpicture_fill((AVPicture*)picture, buffer, PIX_FMT_RGBA, c->width, c->height); 
  
          avpicture_fill((AVPicture*)outpic, outbuffer, PIX_FMT_YUV420P, c->width, c->height);//does not have image data. 
  
  
  
          struct SwsContext* fooContext = sws_getContext(c->width, c->height, 
  
                                                        PIX_FMT_RGBA, 
  
                                                        c->width, c->height, 
  
                                                        PIX_FMT_YUV420P, 
  
                                                        SWS_FAST_BILINEAR, NULL, NULL, NULL); 
  
  
  
          //perform the conversion 
  
          sws_scale(fooContext, picture->data, picture->linesize, 0, c->height, outpic->data, outpic->linesize); 
  
          // Here is where I try to convert to YUV 
  
  
  
          // encode the image 
  
          out_size = avcodec_encode_video(c, outbuf, outbuf_size, outpic); 
  
          printf("encoding frame %3d (size=%5d)\n", i, out_size); 
  
          fwrite(outbuf, 1, out_size, f); 
  
  
  
          free(buffer); 
  
          buffer = NULL;
  
      }
  
  
  
      // get the delayed frames 
  
      for(; out_size; i++) { 
  
          fflush(stdout); 
  
  
  
          out_size = avcodec_encode_video(c, outbuf, outbuf_size, NULL); 
  
          printf("write frame %3d (size=%5d)\n", i, out_size); 
  
          fwrite(outbuf, 1, outbuf_size, f);       
  
      } 
  
  }
  
  
  
  // add sequence end code to have a real mpeg file 
  
  outbuf[0] = 0x00; 
  
  outbuf[1] = 0x00; 
  
  outbuf[2] = 0x01; 
  
  outbuf[3] = 0xb7; 
  
  fwrite(outbuf, 1, 4, f); 
  
  fclose(f); 
  
  free(picture_buf);
  
  free(outbuf); 
  
  
  
  avcodec_close(c); 
  
  av_free(c); 
  
  av_free(picture); 
  
  //av_free(outpic); 
  
  printf("\n"); 

  my msn:hieeli@hotmail.com