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• Python - FFMPEG - Test to see if video file contains DTS audio

  21 décembre 2014, par user3590149

  I’m currently running a script on cron job to convert any video files to .mp4 from .mkv. I use FFMPEG and python 2.7 to accomplish this on FreeBSD and do a native copy for both audio and video which means I leave whatever encoding they use but convert the container mkv to mp4 for DLNA because of compatibility issues for some devices. Some files contain DTS and I want to convert those audio file to AAC/AC3. I only want to convert and trans code audio to AAC/AC3 only if the file has only single audio of DTS. Some files do have DTS and AAC so I would only want to remove the DTS and not trans code in those cases. Is there way I can test a video file and see it if contains a DTS ? Any software I can use like FFMPEG or handbrake ? How would you go about do this ? I’m trying to not lose any quality.

  Psuede Code :

  If file contains DTS:
  
      If file only has single audio track:
  
          convert_to_mp4_AAC_5.1()
  
      else:
  
          remove_DTS(file)
  
          convert_native()
  
  else:
  
      convert_native()

• Remove greenscreen in gif with ffmpeg -filter_complex chromakey without changing the dimesions ?

  22 avril 2021, par MiWe

  I am trying to generate a transparent gif from a video. The chromakey works perfect, but the output gif has smaller dimensions as expected. The transparent borders on the side are cutted. How can I use the chromakey effect without changing the dimesions ?

  


  


  ffmpeg -i input.flv -filter_complex "[0:v]scale='350 :-1',chromakey=0x00ff00:0.2[a] ;[a]palettegen[b]" -map "[b]" palette.png

  


  


  


  ffmpeg.exe -i input.flv -i palette.png -filter_complex "[0:v]scale='350 :-1',chromakey=0x00ff00:0.2[trans] ;[trans][1:v]paletteuse[out]" -map "[out]" output.gif

  


  


• FFmpeg - MJPEG decoding - getting different values

  27 décembre 2016, par ahmadh

  I have a set of JPEG frames which I am muxing into an avi, which gives me a mjpeg video. This is the command I run on the console :

  ffmpeg -y -start_number 0 -i %06d.JPEG -codec copy vid.avi

  When I try to demux the video using ffmpeg C api, I get frames which are slightly different in values. Demuxing code looks something like this :

  AVFormatContext* fmt_ctx = NULL;
  
  AVCodecContext* cdc_ctx = NULL;
  
  AVCodec* vid_cdc = NULL;
  
  int ret;
  
  unsigned int height, width;
  
  
  
  ....
  
  // read_nframes is the number of frames to read
  
  output_arr = new unsigned char [height * width * 3 * 
  
                                  sizeof(unsigned char) * read_nframes];
  
  
  
  avcodec_open2(cdc_ctx, vid_cdc, NULL);
  
  
  
  int num_bytes;
  
  uint8_t* buffer = NULL;
  
  const AVPixelFormat out_format = AV_PIX_FMT_RGB24;
  
  
  
  num_bytes = av_image_get_buffer_size(out_format, width, height, 1);
  
  buffer = (uint8_t*)av_malloc(num_bytes * sizeof(uint8_t));
  
  
  
  AVFrame* vid_frame = NULL;
  
  vid_frame = av_frame_alloc();
  
  AVFrame* conv_frame = NULL;
  
  conv_frame = av_frame_alloc();
  
  
  
  av_image_fill_arrays(conv_frame->data, conv_frame->linesize, buffer, 
  
                       out_format, width, height, 1);
  
  
  
  struct SwsContext *sws_ctx = NULL;
  
  sws_ctx = sws_getContext(width, height, cdc_ctx->pix_fmt,
  
                           width, height, out_format,
  
                           SWS_BILINEAR, NULL,NULL,NULL);
  
  
  
  int frame_num = 0;
  
  AVPacket vid_pckt;
  
  while (av_read_frame(fmt_ctx, &vid_pckt) >=0) {
  
      ret = avcodec_send_packet(cdc_ctx, &vid_pckt);
  
      if (ret < 0)
  
          break;
  
  
  
      ret = avcodec_receive_frame(cdc_ctx, vid_frame);
  
      if (ret < 0 && ret != AVERROR(EAGAIN) && ret != AVERROR_EOF)
  
          break;
  
      if (ret >= 0) {
  
          // convert image from native format to planar GBR
  
          sws_scale(sws_ctx, vid_frame->data, 
  
                    vid_frame->linesize, 0, vid_frame->height, 
  
                    conv_frame->data, conv_frame->linesize);
  
  
  
          unsigned char* r_ptr = output_arr + 
  
              (height * width * sizeof(unsigned char) * 3 * frame_num);
  
          unsigned char* g_ptr = r_ptr + (height * width * sizeof(unsigned char));
  
          unsigned char* b_ptr = g_ptr + (height * width * sizeof(unsigned char));
  
          unsigned int pxl_i = 0;
  
  
  
          for (unsigned int r = 0; r < height; ++r) {
  
              uint8_t* avframe_r = conv_frame->data[0] + r*conv_frame->linesize[0];
  
              for (unsigned int c = 0; c < width; ++c) {
  
                  r_ptr[pxl_i] = avframe_r[0];
  
                  g_ptr[pxl_i]   = avframe_r[1];
  
                  b_ptr[pxl_i]   = avframe_r[2];
  
                  avframe_r += 3;
  
                  ++pxl_i;
  
              }
  
          }
  
  
  
          ++frame_num;
  
  
  
          if (frame_num >= read_nframes)
  
              break;
  
      }
  
  }
  
  
  
  ...

  In my experience around two-thirds of the pixel values are different, each by +-1 (in a range of [0,255]). I am wondering is it due to some decoding scheme FFmpeg uses for reading JPEG frames ? I tried encoding and decoding png frames, and it works perfectly fine.

  In short my goal is to get the same pixel by pixel values for each JPEG frame as I would I have gotten if I was reading the JPEG images directly. Here is the stand-alone code I used. It includes cmake files to build code, and a couple of jpeg frames with the converted avi file to test this problem. (give —filetype png to test the png decoding).