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• Write frame without decoding it ?

  24 août 2016, par Aram

  I’m trying to use dranger tutorials for writing a webcam 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.

  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

• Backslash in Ruby String and Special FFmpeg Characters

  26 novembre 2016, par valii2334

  I enter a string in my xcode project and I send it via api to my rails application where I need to put the string over a picture.

  Let’s say that in xcode (iOS app) I type the string /\%" ’ . The string it’s set in rails ( a field of an object of type string ) like this /\%\" ’ . But the problem is that in convert % and ’ are special characters and I need to prefix them with \ to work (like ruby does with " and \).
  The convert command it’s this :

  command = "convert image.jpg -gravity North -pointsize 40 -fill '#FFFFFF' -annotate +0+50 '#{@text}' image2.jpg"

  @text should contain a string such image2.jpg will contain /\%" ’

  This is just an example with this special characters. It should display any string entered in iOS no metter what language.

• lavu : Add a video section to Doxygen documentation

  10 novembre 2016, par Vittorio Giovara

  lavu : Add a video section to Doxygen documentation
  Fill it with AVStereo3D and AVDisplayMatrix documentation.
  
  Apply the necessary changes to make verbatim code look good in doxygen.
  Signed-off-by : Vittorio Giovara <vittorio.giovara@gmail.com>
  

  • [DBH] libavutil/avutil.h
  • [DBH] libavutil/display.h
  • [DBH] libavutil/stereo3d.h