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• Remux RTSP stream into container ? (Write read frame without decoding it)

  1er septembre 2016, par Aram

  I’m trying to use dranger tutorials for writing a RTSP h264 streamed video directly to a file without decoding and encoding it (ffmpeg 3.0/3.1 library). But I’m a bit lost on how do I need to populate the AVFormatContext pointer for the av_write_frame once I get the corresponding AVPacket.

  Trying to clarify. What I want to do is this

  1. Open webcam stream in h264
  
  2. Read a frame
  
  3. Save it to a file without decoding and encoding it.

  EDIT : I’ve also tried to use the remuxing example in ffmpeg’s documentation (doing a network init()) but I’m getting dts and pts sync errors when going from rtsp -> .mp4

  Copy pasting the code from the tutorial :

  #include 
  
  #include <libavutil></libavutil>pixfmt.h>
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavutil></libavutil>avconfig.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  
  
  int main(int argc, char *argv[]) {
  
      av_register_all();
  
      avcodec_register_all();
  
      avformat_network_init();
  
  
  
      AVFormatContext *pFormatCtx = avformat_alloc_context();
  
  
  
      // Camera comes from argv[1]
  
      avformat_open_input(&amp;pFormatCtx, argv[1], NULL, NULL);
  
      avformat_find_stream_info(pFormatCtx, NULL);
  
      av_dump_format(pFormatCtx, 0, argv[1], 0);
  
  
  
      int video_stream_idx = -1;
  
  
  
      for (int i = 0; i &lt; pFormatCtx->nb_streams; i++) {
  
          if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
  
              video_stream_idx = i;
  
              break;
  
          }
  
      }
  
  
  
      AVCodecContext *pCodecContext = NULL;
  
      AVCodecContext *pCodecContextOrig = NULL;
  
  
  
      pCodecContextOrig = pFormatCtx->streams[video_stream_idx]->codec;
  
      AVCodec *pCodec;
  
      pCodec = avcodec_find_decoder(pCodecContextOrig->codec_id);
  
      pCodecContext = avcodec_alloc_context3(pCodec);
  
      avcodec_copy_context(pCodecContext, pCodecContextOrig);
  
      avcodec_open2(pCodecContext, pCodec, NULL);
  
  
  
      AVFrame *pFrame = av_frame_alloc();
  
      AVFrame *pFrameRGB = av_frame_alloc();
  
  
  
      uint8_t *buffer = NULL;
  
      int buffer_size = avpicture_get_size(AV_PIX_FMT_RGB24, pCodecContext->width,
  
                                           pCodecContext->height);
  
      buffer = (uint8_t *)av_malloc(buffer_size * sizeof(uint8_t));
  
  
  
      // fill buffer
  
      avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_RGB24,
  
                     pCodecContext->width, pCodecContext->height);
  
  
  
      struct SwsContext *sws_ctx = NULL;
  
      int frame_finished = 0;
  
      AVPacket packet;
  
  
  
      // Size(src), fmt(src), Size(dst), fmt(dst) .. flags
  
      sws_ctx = sws_getContext(pCodecContext->width, pCodecContext->height,
  
                               pCodecContext->pix_fmt, pCodecContext->width,
  
                               pCodecContext->height, AV_PIX_FMT_RGB24,
  
                               SWS_BILINEAR, NULL, NULL, NULL);
  
  
  
  
  
      AVFormatContext *out_fmt_ctx;
  
  
  
      avformat_write_header(out_fmt_ctx, NULL);
  
  
  
      int i = 0;
  
      while (i &lt; 100 &amp;&amp; (av_read_frame(pFormatCtx, &amp;packet) >= 0)) {
  
          // Want to write these frames to disk
  
          i++;
  
      }
  
  
  
      av_write_trailer(out_fmt_ctx);
  
  
  
      av_free(buffer);
  
      av_free(pFrameRGB);
  
      av_free(pFrame);
  
  
  
      avcodec_close(pCodecContext);
  
      avcodec_close(pCodecContextOrig);
  
  
  
      avformat_close_input(&amp;pFormatCtx);
  
  
  
      return 0;
  
  }

  I think a lot of stuff of this code can be removed. I’m trying to learn :).

  Linking against -lavutil -lavformat -lavcodec -lz -lavutil -lm -lswscale

• Seek and cut mp4 http stream on the fly with mp4Parser java library

  27 septembre 2016, par xyman

  Is it possible to create new mp4 file(which will be just one small video segment of full length mp4 file) from mp4 http stream without downloading the whole mp4 file to disk and feeding it to mp4Parser. If any other stable java library exist which could do the sam job please point me to it.

  I know it can be done with ffmpeg as explained in this post but i want to avoid using full feature heavy library(cutting the mp4 file doesn’t involve transcoding the video, this operation just repacks the mp4 file) for just cutting the mp4 file.

  ffmpeg -ss 00:01:00.000 -i "http://myfile.mp4" -t 00:02:00.000 -c:a copy -c:v copy output.mp4

• Raw extraction of frames from a movie

  29 septembre 2016, par vkubicki

  I would like to extract images from a grayscale mj2 movie. Each pixel is encoded using 16 bits. Since this is a technical movie, I need to extract the value at each pixel without processing, as those values linearly map to a physical quantity (a heatmap from an infrared camera). I am using Scala, and I do not find any suitable solution for a direct extraction (either in Scala or in Java, but I am a beginner). Therefore I intend to use ffmpeg to extract individual frames on the disk, then load them as BufferedImage in Scala and process them.

  Is this a good approach ? Which format should I use to avoid any transformation in the data ? I want each extracted frame to ba as "raw" as possible ? Is it possible to directly output a csv containing the aforementionned values ?