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• avcodec library not extracting all the frames from a video

  22 novembre 2018, par Guru Govindan

  I have written a library that could be used with python to extract frames from a video in a buffer for some processing. I used the examples from the ffmpeg to build my library using libavcodec.
  This and seems to be working fine for most of the videos. But I see on some videos where my library does not extract all the frames (way less than the FPS).

  It seems like somehow the packets might be out of order and docoder is not able to handle it. I keep getting a lot of the following errors

  pid=100 pes_code=0x1e0

  nal_unit_type : 9, nal_ref_idc : 0

  nal_unit_type : 1, nal_ref_idc : 2

  deblocking_filter_idc 7 out of range

  decode_slice_header error

  no frame !

  I use the following steps to setup the decoder.

      //open input file, allocate context
  
  if ((ret = avformat_open_input(&format_ctx, in_filename, 0, 0)) < 0) {
  
      PyErr_SetString(ExtractorError, "Could not open input file!");
  
      goto end;
  
  }
  
  
  
  if ((ret = avformat_find_stream_info(format_ctx, 0)) < 0) {
  
      PyErr_SetString(ExtractorError, "Failed to retrieve input stream information!");
  
      goto end;
  
  }
  
  
  
  av_dump_format(format_ctx, 0, in_filename, 0);
  
  
  
  // Get the video index from the stream
  
  for(int i=0; inb_streams ;i++ )
  
  {
  
      if( format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO )
  
      {
  
          video_stream_index = i;
  
          break;
  
      }
  
  }
  
  
  
  /* if video stream not availabe */
  
  if((video_stream_index) == -1)
  
  {
  
      PyErr_SetString(ExtractorError, "video stream to retreive fps is not found!");
  
      return NULL;
  
  }
  
  
  
  long duration = format_ctx->duration + (format_ctx->duration <= INT64_MAX - 5000 ? 5000 : 0);
  
  
  
  float duration_in_secs = (float)duration / AV_TIME_BASE;
  
  
  
  stream_mapping_size = format_ctx->nb_streams;
  
  stream_mapping = av_mallocz_array(stream_mapping_size, sizeof(*stream_mapping));
  
  if (!stream_mapping) {
  
      ret = AVERROR(ENOMEM);
  
      goto end;
  
  }
  
  
  
  AVCodec *pCodec = NULL;
  
  AVCodecParameters *in_codecpar = NULL;
  
  for (i = 0; i < format_ctx->nb_streams; i++) {
  
      AVStream *in_stream = format_ctx->streams[i];
  
      in_codecpar = in_stream->codecpar;
  
  
  
      if (in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO &&
  
          in_codecpar->codec_type != AVMEDIA_TYPE_VIDEO &&
  
          in_codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE) {
  
          stream_mapping[i] = -1;
  
          continue;
  
      }
  
  
  
      if (in_codecpar->codec_type == AVMEDIA_TYPE_VIDEO){
  
          pCodec = avcodec_find_decoder(in_codecpar->codec_id);
  
          stream_mapping[i] = stream_index++;
  
          break;
  
      }
  
  }
  
  
  
  if(!pCodec){
  
      PyErr_SetString(ExtractorError, "error, no pCodec!");
  
      return NULL;
  
  }
  
  
  
  // convert CodecParam to CodecCtx
  
  AVCodecContext *pCodecCtx = avcodec_alloc_context3(pCodec);
  
  if (!pCodecCtx) {
  
      PyErr_SetString(ExtractorError, "Failed to convert codecParam to CodecCtx!");
  
      return NULL;
  
  }
  
  
  
  ret = avcodec_parameters_to_context(pCodecCtx, in_codecpar);
  
  if (ret < 0)
  
      goto end;
  
  
  
  //open video decoder
  
  if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
  
  {
  
      logging("EXTRACTOR: failed to open codec through avcodec_open2\n");
  
      return NULL;
  
  }

  In order to test it I used the following command from ffmpeg to extract frames from the same video and it worked fine.

  ffmpeg -i /thuuz/extractor/03000.ts -f image2 -qscale:v 7 ffmpeg-detect—%03d.jpg -hide_banner -v quiet

  Am I not passing the right codec params ? Please let me know some inputs on how to debug this issue.
  Thanks a lot.

• How can I fix a audio delay caused by a batch trim of the start and end of a video file

  15 mai 2019, par trozz

  When using this ffmpeg batch trimmer I found on here - will be posted down below in "show code" Tried to format it correctly, but I’m new here so.

  It causes the audio to be delayed by 100 milliseconds. Is there a way to fix this in the same bat file, or maybe after with another edit ?

  Thanks

  @Echo Off
  
  SetLocal
  
  
  
  Set "ext=mp4"
  
  
  
  Set "opts=-v quiet"
  
  
  
  Set "opts=%opts% -print_format "compact=print_section=0:nokey=1:escape=csv"
  
  
  
  Set "opts=%opts% -show_entries "format=duration""
  
  
  
  If Exist *.%ext% (If Not Exist "Trimmed\" MD Trimmed)
  
  
  
  For %%a In (*.%ext%) Do Call :Sub "%%~a"
  
  
  
  Exit/B
  
  
  
  :Sub
  
  
  
  For /f "Tokens=1* Delims=." %%a In (
  
      'FFProbe %opts% %1') Do (Set/A "ws=%%a-7.85" & Set "ps=%%b")
  
  
  
  rem If %ws% Lss 20 GoTo :EOF
  
  
  
  Set/A hh=ws/(60*60), lo=ws%%(60*60), mm=lo/60, ss=lo%%60
  
  
  
  If %hh% Lss 10 Set hh=0%hh%
  
  
  
  If %mm% Lss 10 Set mm=0%mm%
  
  
  
  If %ss% Lss 10 Set ss=0%ss%
  
  
  
  FFMpeg -i %1 -ss 00:00:04.5000 -to %hh%:%mm%:%ss%.%ps:~,3% -c:v copy -c:a copy "Trimmed\%~1"

• Why aren't the videos in my S3 bucket buffering to html video tag ?

  2 juin 2019, par Michael Cain

  I have so far successfully programmed a node script on a Udoo x86 advanced plus that captures an Ethernet connected IP cam’s RTSP stream. I use ffmpeg to trans-code the stream into 5 second mp4 files. As soon as the files show up in the folder they are uploaded/synced to my AWS S3 Bucket. Next I have a Node server that GET’s the most recently created mp4 file from the S3 bucket and runs it through mediasource extension and finally to an html video tag.

  The videos are playing on the browser but not in any kind of synchronous manner. No buffering seems to be taking place. one video plays then another and so on. Video is skipping all over the place.

  I would really appreciate any guidance with this bug.

  export function startlivestream() {
  
    const videoElement = document.getElementById("my-video");
  
    const myMediaSource = new MediaSource();
  
    const url = URL.createObjectURL(myMediaSource);
  
    videoElement.src = url;
  
    myMediaSource.addEventListener("sourceopen", sourceOpen);
  
  }
  
  function sourceOpen() {
  
    if (window.MediaSource.isTypeSupported(
  
        'video/mp4; codecs="avc1.42E01E, mp4a.40.2"'
  
      )
  
    ) 
  
  {
  
         console.log("YES");
  
    }
  
  
  
  // 1. add source buffers
  
  
  
    const mediaCodec = 'video/mp4; codecs="avc1.4D601F"';
  
    var mediasource = this;
  
    const videoSourceBuffer = mediasource.addSourceBuffer(mediaCodec);
  
  
  
  // 2. download and add our audio/video to the SourceBuffers
  
  
  
  function checkVideo(url) {
  
    var oReq = new XMLHttpRequest();
  
      oReq.open("GET", url, true);
  
      oReq.responseType = "arraybuffer";
  
  
  
       oReq.onload = function(oEvent) {
  
        var arrayBuffer = oReq.response; // Note: not oReq.responseText
  
        if (arrayBuffer) {
  
           videoSourceBuffer.addEventListener("updateend", function(_) {
  
             mediasource.endOfStream();
  
             document.getElementById("my-video").play();
  
     });
  
             videoSourceBuffer.appendBuffer(arrayBuffer);
  
        }
  
      };
  
  
  
      oReq.send(null);
  
    }
  
  
  
    setInterval(function() {
  
      checkVideo("http://localhost:8080");
  
    }, 5000);

  My ffmpeg tags :

  const startRecording = () => {
  
    const args = [
  
      "-rtsp_transport",
  
      "tcp",
  
      "-i",
  
      inputURL,
  
      "-f",
  
      "segment",
  
      "-segment_time",
  
      "5",
  
      "-segment_format",
  
      "mp4",
  
      "-segment_format_options",
  
      "movflags=frag_keyframe+empty_moov+default_base_moof",
  
      "-segment_time",
  
      "5",
  
      "-segment_list_type",
  
      "m3u8",
  
      "-c:v",
  
      "copy",
  
      "-strftime",
  
      "1",
  
      `${path.join(savePath, "test-%Y-%m-%dT%H-%M-%S.mp4")}`
  
    ];

  From what I have learned about Mediasource extensions they allow multiple videos to be taken in and allow the client to buffer them so it looks like one longer video. In simple terms.