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• Adding a text on top of video using libavfilter API

  19 février 2013, par prajwal

  I am trying to add a visible text ‘sampletext’ on a video and store in another file called “myvideo.mp4”

  Below is my code.(developed from *doc/examples/filtering_video.c *example)

  include

  #define _XOPEN_SOURCE 600 /* for usleep */
  
  
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavfilter></libavfilter>avfiltergraph.h>
  
  #include <libavfilter></libavfilter>avcodec.h>
  
  #include <libavfilter></libavfilter>buffersink.h>
  
  #include <libavfilter></libavfilter>buffersrc.h>
  
  
  
  const char *filter_descr = "drawtext=fontcolor=white:fontfile=/usr/share/fonts/liberation/LiberationMono-Bold.ttf :rate=30000/1001:text=&#39;sampletext&#39;";
  
  
  
  static AVFormatContext *fmt_ctx;
  
  static AVCodecContext *dec_ctx;
  
  AVFilterContext *buffersink_ctx;
  
  AVFilterContext *buffersrc_ctx;
  
  AVFilterGraph *filter_graph;
  
  static int video_stream_index = -1;
  
  static int64_t last_pts = AV_NOPTS_VALUE;
  
  
  
  static int open_input_file(const char *filename)
  
  {
  
      int ret;
  
      AVCodec *dec;
  
  
  
      if ((ret = avformat_open_input(&amp;fmt_ctx, filename, NULL, NULL)) &lt; 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
  
          return ret;
  
      }
  
  
  
      if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) &lt; 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
  
          return ret;
  
      }
  
  
  
      /* select the video stream */
  
      ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &amp;dec, 0);
  
      if (ret &lt; 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n");
  
          return ret;
  
      }
  
      video_stream_index = ret;
  
      dec_ctx = fmt_ctx->streams[video_stream_index]->codec;
  
  
  
      /* init the video decoder */
  
      if ((ret = avcodec_open2(dec_ctx, dec, NULL)) &lt; 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");
  
          return ret;
  
      }
  
  
  
      return 0;
  
  }
  
  
  
  static int init_filters(const char *filters_descr)
  
  {
  
      char args[512];
  
      int ret;
  
      AVFilter *buffersrc  = avfilter_get_by_name("buffer");
  
      AVFilter *buffersink = avfilter_get_by_name("ffbuffersink");
  
      AVFilterInOut *outputs = avfilter_inout_alloc();
  
      AVFilterInOut *inputs  = avfilter_inout_alloc();
  
      enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };
  
      AVBufferSinkParams *buffersink_params;
  
  
  
      filter_graph = avfilter_graph_alloc();
  
  
  
      /* buffer video source: the decoded frames from the decoder will be inserted here. */
  
      snprintf(args, sizeof(args),
  
              "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
  
              dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,
  
              dec_ctx->time_base.num, dec_ctx->time_base.den,
  
              dec_ctx->sample_aspect_ratio.num, dec_ctx->sample_aspect_ratio.den);
  
  
  
      ret = avfilter_graph_create_filter(&amp;buffersrc_ctx, buffersrc, "in",
  
                                         args, NULL, filter_graph);
  
      if (ret &lt; 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");
  
          return ret;
  
      }
  
  
  
      /* buffer video sink: to terminate the filter chain. */
  
      buffersink_params = av_buffersink_params_alloc();
  
      buffersink_params->pixel_fmts = pix_fmts;
  
      ret = avfilter_graph_create_filter(&amp;buffersink_ctx, buffersink, "out",
  
                                         NULL, buffersink_params, filter_graph);
  
      av_free(buffersink_params);
  
      if (ret &lt; 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");
  
          return ret;
  
      }
  
  
  
      /* Endpoints for the filter graph. */
  
      outputs->name       = av_strdup("in");
  
      outputs->filter_ctx = buffersrc_ctx;
  
      outputs->pad_idx    = 0;
  
      outputs->next       = NULL;
  
  
  
      inputs->name       = av_strdup("out");
  
      inputs->filter_ctx = buffersink_ctx;
  
      inputs->pad_idx    = 0;
  
      inputs->next       = NULL;
  
  
  
      if ((ret = avfilter_graph_parse(filter_graph, filters_descr,
  
                                      &amp;inputs, &amp;outputs, NULL)) &lt; 0)
  
          return ret;
  
  
  
      if ((ret = avfilter_graph_config(filter_graph, NULL)) &lt; 0)
  
          return ret;
  
      return 0;
  
  }
  
  
  
  static void save_picref(AVFilterBufferRef *picref, AVRational time_base)
  
  {
  
      int x, y;
  
      uint8_t *p0, *p;
  
      int64_t delay;
  
      FILE *pFile;
  
    char szFilename[32]="myvideo.mp4";
  
  
  
    // Open file
  
      pFile=fopen(szFilename, "wb");
  
    if(pFile==NULL)
  
      return;
  
  
  
      if (picref->pts != AV_NOPTS_VALUE) {
  
          if (last_pts != AV_NOPTS_VALUE) {
  
              /* sleep roughly the right amount of time;
  
               * usleep is in microseconds, just like AV_TIME_BASE. */
  
              delay = av_rescale_q(picref->pts - last_pts,
  
                                   time_base, AV_TIME_BASE_Q);
  
              if (delay > 0 &amp;&amp; delay &lt; 1000000)
  
                  usleep(delay);
  
          }
  
          last_pts = picref->pts;
  
      }
  
    fprintf(pFile, "P6\n%d %d\n255\n", picref->video->w, picref->video->h);
  
      // Write pixel data
  
      for (y = 0; y &lt; picref->video->h; y++) {
  
      p = p0;
  
  
  
      fwrite(picref->data[0], 1, picref->video->w, pFile);
  
  
  
      p0 += picref->linesize[0];
  
      }
  
    // Close file
  
    fclose(pFile);
  
  
  
  }
  
  
  
  int main(int argc, char **argv)
  
  {
  
      int ret;
  
      AVPacket packet;
  
      AVFrame frame;
  
      int got_frame;
  
  
  
      if (argc != 2) {
  
          fprintf(stderr, "Usage: %s file\n", argv[0]);
  
          exit(1);
  
      }
  
  
  
      avcodec_register_all();
  
      av_register_all();
  
      avfilter_register_all();
  
  
  
      if ((ret = open_input_file(argv[1])) &lt; 0)
  
          goto end;
  
      if ((ret = init_filters(filter_descr)) &lt; 0)
  
          goto end;
  
  
  
      /* read all packets */
  
      while (1) {
  
          AVFilterBufferRef *picref;
  
          if ((ret = av_read_frame(fmt_ctx, &amp;packet)) &lt; 0)
  
              break;
  
  
  
          if (packet.stream_index == video_stream_index) {
  
              avcodec_get_frame_defaults(&amp;frame);
  
              got_frame = 0;
  
              ret = avcodec_decode_video2(dec_ctx, &amp;frame, &amp;got_frame, &amp;packet);
  
              if (ret &lt; 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Error decoding video\n");
  
                  break;
  
              }
  
  
  
              if (got_frame) {
  
                  frame.pts = av_frame_get_best_effort_timestamp(&amp;frame);
  
  
  
                  /* push the decoded frame into the filtergraph */
  
                  if (av_buffersrc_add_frame(buffersrc_ctx, &amp;frame, 0) &lt; 0) {
  
                      av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
  
                      break;
  
                  }
  
  
  
                  /* pull filtered pictures from the filtergraph */
  
                  while (1) {
  
                      ret = av_buffersink_get_buffer_ref(buffersink_ctx, &amp;picref, 0);
  
                      if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
                          break;
  
                      if (ret &lt; 0)
  
                          goto end;
  
  
  
                      if (picref) {
  
                          save_picref(picref, buffersink_ctx->inputs[0]->time_base);
  
                          avfilter_unref_bufferp(&amp;picref);
  
                      }
  
                  }
  
              }
  
          }
  
          av_free_packet(&amp;packet);
  
      }
  
  end:
  
      avfilter_graph_free(&amp;filter_graph);
  
      if (dec_ctx)
  
          avcodec_close(dec_ctx);
  
      avformat_close_input(&amp;fmt_ctx);
  
  
  
      if (ret &lt; 0 &amp;&amp; ret != AVERROR_EOF) {
  
          char buf[1024];
  
          av_strerror(ret, buf, sizeof(buf));
  
          fprintf(stderr, "Error occurred: %s\n", buf);
  
          exit(1);
  
      }
  
  
  
      exit(0);
  
  }

  After compilation and execution, when I try to play the video using

  ffplay myvideo.mp4 *

  I am getting the following error.

  myvideo.mp4 : Invalid data found when processing input*

  i am unable to resolve the error,can anyone pls help me out in solving the error.

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