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• Does converting .mp4 to .mkv change data fidelity ?

  31 décembre 2020, par Will Pike

  I am wondering when I convert a .mp4 to .mkv using the following command if the quality changes.

  


  ffmpeg -i in.mp4 out.mkv


  


  The input file, in.mp4 has a file size of 297 megabytes, while the out.mkv file has a size of 249 megabytes, 15% lower. Upon manual inspection, the resolution, video, and audio streams are the same before/after (as I would have expected given my (limited) knowledge of ffmpeg).

  


  Is the 15% size decrease by simply converting to mkv actually not affect the quality of the video ? If so this seems like a very reasonable way of freeing up some space on my computer.

  


• ffmpeg av_read_frame "Invalid data found"

  26 mai 2017, par DweebsUnited

  I am using ffmpeg to cut part of a file, following the remux example provided. However, I am having issues reading from files. I am given a file descriptor as input and an output filename, and can successfully set up the output file, read the stream info, copy all the streams, etc, etc. On the first call to av_read_frame though, I get an "Invalid data found when processing input" error. I have tried this with many different video files, and have not been able to get a single one to process correctly.

  Here is my code. I get no errors anywhere, except av_read_frame, which gives Invalid data found no matter what video file I give it.

  char path[512];
  
  sprintf(path, "pipe:%d", fileno(fp));
  
  
  
  
  
  AVOutputFormat *ofmt = NULL;
  
  AVFormatContext *ifmt_ctx = avformat_alloc_context(), *ofmt_ctx = NULL;
  
  AVPacket pkt;
  
  int ret, i;
  
  
  
  av_register_all();
  
  avcodec_register_all();
  
  
  
  if ((ret = avformat_open_input(&ifmt_ctx, path, av_find_input_format("mp4"), NULL)) < 0) {
  
      LOG("Could not open input file '%s'", path);
  
      goto end;
  
  }
  
  
  
  if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
  
      LOG("Failed to retrieve input stream information", "");
  
      goto end;
  
  }
  
  
  
  avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
  
  if (!ofmt_ctx) {
  
      LOG("Could not create output context\n");
  
      ret = AVERROR_UNKNOWN;
  
      goto end;
  
  }
  
  
  
  ofmt = ofmt_ctx->oformat;
  
  
  
  for (i = 0; i < ifmt_ctx->nb_streams; i++) {
  
      AVStream *in_stream = ifmt_ctx->streams[i];
  
      AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
  
  
  
      if (!out_stream) {
  
          LOG("Failed allocating output stream\n");
  
          goto end;
  
      }
  
  
  
      ret = avcodec_parameters_copy(out_stream->codecpar, in_stream->codecpar);
  
      if (ret < 0) {
  
          LOG("Failed to copy context from input to output stream codec context\n");
  
          goto end;
  
      }
  
      out_stream->codecpar->codec_tag = 0;
  
  }
  
  
  
  if (!(ofmt->flags & AVFMT_NOFILE)) {
  
      ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
  
      if (ret < 0) {
  
          LOG("Could not open output file '%s'", out_filename);
  
          goto end;
  
      }
  
  }
  
  
  
  ret = avformat_write_header(ofmt_ctx, NULL);
  
  if (ret < 0) {
  
      LOG("Error occurred when opening output file\n");
  
      goto end;
  
  }
  
  
  
  //    int indexs[8] = {0};
  
  
  
  //    int64_t start_from = 8*AV_TIME_BASE;
  
  ret = av_seek_frame(ifmt_ctx, -1, from_seconds*AV_TIME_BASE, AVSEEK_FLAG_ANY);
  
  if (ret < 0) {
  
      LOG("Error seek\n");
  
      goto end;
  
  }
  
  
  
  int64_t *dts_start_from;
  
  int64_t *pts_start_from;
  
  dts_start_from = (int64_t *) malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
  
  memset(dts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);
  
  pts_start_from = (int64_t *) malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
  
  memset(pts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);
  
  
  
  while (1) {
  
      AVStream *in_stream, *out_stream;
  
  
  
      ret = av_read_frame(ifmt_ctx, &pkt);
  
      if (ret < 0)
  
          break;
  
  
  
      in_stream = ifmt_ctx->streams[pkt.stream_index];
  
      out_stream = ofmt_ctx->streams[pkt.stream_index];
  
  
  
      if (av_q2d(in_stream->time_base) * pkt.pts > end_seconds) {
  
          av_packet_unref(&pkt);
  
          break;
  
      }
  
  
  
      if (dts_start_from[pkt.stream_index] == 0)
  
          dts_start_from[pkt.stream_index] = pkt.dts;
  
      if (pts_start_from[pkt.stream_index] == 0)
  
          pts_start_from[pkt.stream_index] = pkt.pts;
  
  
  
      /* copy packet */
  
      pkt.pts = ::av_rescale_q_rnd(pkt.pts - pts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, (AVRounding) (AV_ROUND_NEAR_INF |
  
                                                                                                                                          AV_ROUND_PASS_MINMAX));
  
      pkt.dts = ::av_rescale_q_rnd(pkt.dts - dts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, (AVRounding) (AV_ROUND_NEAR_INF |
  
                                                                                                                                          AV_ROUND_PASS_MINMAX));
  
      if (pkt.pts < 0) {
  
          pkt.pts = 0;
  
      }
  
      if (pkt.dts < 0) {
  
          pkt.dts = 0;
  
      }
  
      pkt.duration = (int) av_rescale_q((int64_t) pkt.duration, in_stream->time_base, out_stream->time_base);
  
      pkt.pos = -1;
  
  
  
      ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
  
      if (ret < 0) {
  
          LOG("Error muxing packet\n");
  
          break;
  
      }
  
      av_packet_unref(&pkt);
  
  }
  
  free(dts_start_from);
  
  free(pts_start_from);
  
  
  
  av_write_trailer(ofmt_ctx);
  
  
  
  end:
  
  LOG("END");
  
  
  
  avformat_close_input(&ifmt_ctx);
  
  
  
  /* close output */
  
  if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
  
      avio_closep(&ofmt_ctx->pb);
  
  avformat_free_context(ofmt_ctx);
  
  
  
  if (ret < 0 && ret != AVERROR_EOF) {
  
      LOG("-- Error occurred: %s\n", av_err2str(ret));
  
      return 1;
  
  }

  Thank you for any help, I’m still getting used to ffmpeg. Did I miss some setting on the input ? Am I not setting something up that I need to be ? This problem is really stumping me.

• How to read file from"/data/user/0com.package.name/files/ffmpeg" ? in Android ?

  4 septembre 2021, par Thriller Mobiles

  How to read file from "/data/user/0com.package.name/files/ffmpeg" in Android ? I'm using FFMPEG lib version 2.4.2 with com.github.hiteshsondhi88 this reference.