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• Losing quality when encoding with ffmpeg

  22 mai 2016, par lupod

  I am using the c libraries of ffmpeg to read frames from a video and create an output file that is supposed to be identical to the input.
  However, somewhere during this process some quality gets lost and the result is "less sharp". My guess is that the problem is the encoding and that the frames are too compressed (also because the size of the file decreases quite significantly). Is there some parameter in the encoder that allows me to control the quality of the result ? I found that AVCodecContext has a compression_level member, but changing it that does not seem to have any effect.

  I post here part of my code in case it could help. I would say that something must be changed in the init function of OutputVideoBuilder when I set the codec. The AVCodecContext that is passed to the method is the same of InputVideoHandler.
  Here are the two main classes that I created to wrap the ffmpeg functionalities :

  // This class opens the video files and sets the decoder
  
  class InputVideoHandler {
  
  public:
  
    InputVideoHandler(char* name);
  
    ~InputVideoHandler();
  
    AVCodecContext* getCodecContext();
  
    bool readFrame(AVFrame* frame, int* success);
  
  
  
  private:
  
    InputVideoHandler();
  
    void init(char* name);
  
    AVFormatContext* formatCtx;
  
    AVCodec* codec;
  
    AVCodecContext* codecCtx;
  
    AVPacket packet;
  
    int streamIndex;
  
  };
  
  
  
  void InputVideoHandler::init(char* name) {
  
    streamIndex = -1;
  
    int numStreams;
  
  
  
    if (avformat_open_input(&formatCtx, name, NULL, NULL) != 0)
  
      throw std::exception("Invalid input file name.");
  
  
  
    if (avformat_find_stream_info(formatCtx, NULL)<0)
  
      throw std::exception("Could not find stream information.");
  
  
  
    numStreams = formatCtx->nb_streams;
  
  
  
    if (numStreams < 0)
  
      throw std::exception("No streams in input video file.");
  
  
  
    for (int i = 0; i < numStreams; i++) {
  
      if (formatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
  
        streamIndex = i;
  
        break;
  
      }
  
    }
  
  
  
    if (streamIndex < 0)
  
      throw std::exception("No video stream in input video file.");
  
  
  
    // find decoder using id
  
    codec = avcodec_find_decoder(formatCtx->streams[streamIndex]->codec->codec_id);
  
    if (codec == nullptr)
  
      throw std::exception("Could not find suitable decoder for input file.");
  
  
  
    // copy context from input stream
  
    codecCtx = avcodec_alloc_context3(codec);
  
    if (avcodec_copy_context(codecCtx, formatCtx->streams[streamIndex]->codec) != 0)
  
      throw std::exception("Could not copy codec context from input stream.");
  
  
  
    if (avcodec_open2(codecCtx, codec, NULL) < 0)
  
      throw std::exception("Could not open decoder.");
  
  }
  
  
  
  // frame must be initialized with av_frame_alloc() before!
  
  // Returns true if there are other frames, false if not.
  
  // success == 1 if frame is valid, 0 if not.
  
  bool InputVideoHandler::readFrame(AVFrame* frame, int* success) {
  
    *success = 0;
  
    if (av_read_frame(formatCtx, &packet) < 0)
  
      return false;
  
    if (packet.stream_index == streamIndex) {
  
      avcodec_decode_video2(codecCtx, frame, success, &packet);
  
    }
  
    av_free_packet(&packet);
  
    return true;
  
  }
  
  
  
  // This class opens the output and write frames to it
  
  class OutputVideoBuilder{
  
  public:
  
    OutputVideoBuilder(char* name, AVCodecContext* inputCtx);
  
    ~OutputVideoBuilder();
  
    void writeFrame(AVFrame* frame);
  
    void writeVideo();
  
  
  
  private:
  
    OutputVideoBuilder();
  
    void init(char* name, AVCodecContext* inputCtx);
  
    void logMsg(AVPacket* packet, AVRational* tb);
  
    AVFormatContext* formatCtx;
  
    AVCodec* codec;
  
    AVCodecContext* codecCtx;
  
    AVStream* stream;
  
  };
  
  
  
  void OutputVideoBuilder::init(char* name, AVCodecContext* inputCtx) {
  
    if (avformat_alloc_output_context2(&formatCtx, NULL, NULL, name) < 0)
  
      throw std::exception("Could not determine file extension from provided name.");
  
  
  
    codec = avcodec_find_encoder(inputCtx->codec_id);
  
    if (codec == nullptr) {
  
      throw std::exception("Could not find suitable encoder.");
  
    }
  
  
  
    codecCtx = avcodec_alloc_context3(codec);
  
    if (avcodec_copy_context(codecCtx, inputCtx) < 0)
  
      throw std::exception("Could not copy output codec context from input");
  
  
  
    codecCtx->time_base = inputCtx->time_base;
  
    codecCtx->compression_level = 0;
  
  
  
    if (avcodec_open2(codecCtx, codec, NULL) < 0)
  
      throw std::exception("Could not open encoder.");
  
  
  
    stream = avformat_new_stream(formatCtx, codec);
  
    if (stream == nullptr) {
  
      throw std::exception("Could not allocate stream.");
  
    }
  
  
  
    stream->id = formatCtx->nb_streams - 1;
  
    stream->codec = codecCtx;
  
    stream->time_base = codecCtx->time_base;
  
  
  
  
  
  
  
    av_dump_format(formatCtx, 0, name, 1);
  
    if (!(formatCtx->oformat->flags & AVFMT_NOFILE)) {
  
      if (avio_open(&formatCtx->pb, name, AVIO_FLAG_WRITE) < 0) {
  
        throw std::exception("Could not open output file.");
  
      }
  
    }
  
  
  
    if (avformat_write_header(formatCtx, NULL) < 0) {
  
      throw std::exception("Error occurred when opening output file.");
  
    }
  
  
  
  }
  
  
  
  void OutputVideoBuilder::writeFrame(AVFrame* frame) {
  
    AVPacket packet = { 0 };
  
    int success;
  
    av_init_packet(&packet);
  
  
  
    if (avcodec_encode_video2(codecCtx, &packet, frame, &success))
  
      throw std::exception("Error encoding frames");
  
  
  
    if (success) {
  
      av_packet_rescale_ts(&packet, codecCtx->time_base, stream->time_base);
  
      packet.stream_index = stream->index;
  
      logMsg(&packet,&stream->time_base);
  
      av_interleaved_write_frame(formatCtx, &packet);
  
    }
  
    av_free_packet(&packet);
  
  }

  This is the part of the main function that reads and write frames :

   while (inputHandler->readFrame(frame,&gotFrame)) {
  
  
  
      if (gotFrame) {
  
        try {
  
          outputBuilder->writeFrame(frame);
  
        }
  
        catch (std::exception e) {
  
          std::cout << e.what() << std::endl;
  
          return -1;
  
        }
  
      }
  
    }

• How to estimate in Node audio bitrate, bytes, duration without ffmpeg

  6 mai 2016, par loretoparisi

  Supposed to not have access to ffmpeg I need a simple way to calculate the bitrate of an audio (or video) file given media length (bytes) and duration (seconds), i.e. the function

  bitrate = MediaInfo.bitrate(bytes, duration);

  Also I need to do the opposite, so that given approximate media bitrate and length I need calculate the duration :

  duration = MediaInfo.duration(bytes, bitrate);

  So, this is my attempt, inspired by bitrate node module :

  var console = {
  
      log: function(s) {
  
        document.getElementById("console").innerHTML += s + "<br />"
  
      }
  
  }
  
  
  
  /**
  
   * Get media file info
  
   * @see https://www.npmjs.com/package/bitrate
  
   * * @author Loreto Parisi (loretoparisi at gmail dot com)
  
   */
  
  var MediaInfo = {
  
  
  
      /** unit divisors */
  
      DIVISORS : {
  
        bps: 0.125,
  
        kbps: 125,
  
        mbps: 125000,
  
        Bps: 1,
  
        KBps: 1000,
  
        MBps: 1000000
  
      },
  
  
  
      /**
  
       * Calcuate approximate bitrate
  
       * @param bytes integer media length in bytes
  
       * @param seconds float media duration
  
       * @param format string: bps|kbps|Bps|KBps|MBps
  
       * @param pos integer decimal approximation
  
      */
  
      bitrate : function(bytes, seconds, format, pos) {
  
              if (typeof format !== 'string') throw new TypeError('Expected \'format\' to be a string')
  
              format = format.replace('/', 'p')
  
  
  
        var divisor = this.DIVISORS[format];
  
              if (!divisor) throw new Error('\'format\' is an invalid string')
  
        var bitrate = bytes / seconds / divisor;
  
        pos=pos||4;
  
  
  
        return (Math.round(bitrate * Math.pow(10,pos)) / Math.pow(10,pos) );
  
  
  
      },
  
  
  
      /**
  
       * Calcuate media bytes
  
       * @param bitrate float media bitrate per seconds
  
       * @param seconds float media duration
  
       * @param format string: bps|kbps|Bps|KBps|MBps
  
       * @param pos integer decimal approximation
  
      */
  
      bytes : function(bitrate, seconds, format) {
  
         if (typeof format !== 'string') throw new TypeError('Expected \'format\' to be a string')
  
         format = format.replace('/', 'p')
  
  
  
         var divisor = this.DIVISORS[format];
  
         if (!divisor) throw new Error('\'format\' is an invalid string')
  
         var bytes = bitrate * seconds * divisor;
  
  
  
         return ( Math.round(bytes) );
  
  
  
       }, //bytes
  
  
  
      /**
  
       * Calcuate approximate duration
  
       * @param bytes integer media length in bytes
  
       * @param bitrate float media bitrate per seconds
  
       * @param format string: bps|kbps|Bps|KBps|MBps
  
       * @param pos integer decimal approximation
  
      */
  
      duration : function(bytes, bitrate, format, pos) {
  
        if (typeof format !== 'string') throw new TypeError('Expected \'format\' to be a string')
  
              format = format.replace('/', 'p')
  
  
  
        var divisor = this.DIVISORS[format];
  
        if (!divisor) throw new Error('\'format\' is an invalid string')
  
        var seconds = bytes / bitrate / divisor;
  
        pos=pos||4;
  
  
  
        return (Math.round(seconds * Math.pow(10,pos)) / Math.pow(10,pos) );
  
      }
  
    } //MediaInfo
  
  
  
  // example of usage
  
    var bytes = 57511; // media file size in bytes
  
    var seconds = 20.35 // media file duration in seconds
  
  
  
    // calculate media bitrate given media length and duration
  
    var kilobitsPerSecond = MediaInfo.bitrate(bytes, seconds, 'kbps', 3) // => 326.3
  
    var bitsPerSecond = MediaInfo.bitrate(bytes, seconds, 'bps', 3) // => 326279
  
    var BytesPerSecond = MediaInfo.bitrate(bytes, seconds, 'Bps', 3) // => 40785
  
  
  
    // inverse: calculate media duration given media length and bitrate
  
    var duration = MediaInfo.duration(bytes, kilobitsPerSecond, 'kbps', 3);
  
    
  
    // estimated bytes length given bitrate and duration
  
    var estimatedBytes = MediaInfo.bytes(kilobitsPerSecond, duration, 'kbps', 3);
  
  
  
    var data = {
  
        bytes : bytes,
  
        seconds : seconds,
  
        kilobitsPerSecond : kilobitsPerSecond + " kb/s",
  
        bitsPerSecond : bitsPerSecond + " b/s",
  
        BytesPerSecond : BytesPerSecond + " B/s",
  
        duration : duration,
  
       estimatedBytes : estimatedBytes
  
    }
  
  
  
    console.log( JSON.stringify(data, null, 2) );

  <div></div>

  The result media info are

  {
  
    "bytes": 57511,
  
    "seconds": 20.35,
  
    "kilobitsPerSecond": "22.609 kb/s",
  
    "bitsPerSecond": "22608.747 b/s",
  
    "BytesPerSecond": "2826.093 B/s",
  
    "duration": 20.35,
  
    "estimatedBytes": 57512
  
  }

  while ffmpeg gives

  Duration: 00:00:20.35, start: 0.000000, bitrate: 22 kb/s
  
      Stream #0:0(eng): Audio: aac (mp4a / 0x6134706D), 8000 Hz, mono, fltp, 16 kb/s (default)

  Of course, the problem here is the assumption that I have a fixed bitrate when calculating the duration. But, is there any other way without having ffprobe or lame in node ?

  Note. A good options, where the media file has ID3 tagging, is to use the JSMediaTags node module that supports ID3 and MP4 tagging for media files and works both in the browser that in node :

  var jsmediatags = require("jsmediatags");
  
  jsmediatags.read("./music-file.mp3", {
  
    onSuccess: function(tag) {
  
      console.log(tag);
  
    },
  
    onError: function(error) {
  
      console.log(':(', error.type, error.info);
  
    }
  
  });

  This will not work for streaming media files or for files coming from direct audio sources of course.

• ffmpeg error : Data doesn't look like RTP packets, make sure the RTP muxer is used

  29 juin 2016, par SOFuser

  I am trying to stream both video&audio from usbcam&mic throw ffmpeg over ffserver
  I got 2 errors :
  - ffmpeg seems functionning but showing "Data doesn’t look like RTP packets, make sure the RTP muxer is used"
  - i can connect to ffserver only for static files

  here is server.conf file :

  HTTPPort 1235
  
  RTSPPort 1234
  
  HTTPBindAddress 0.0.0.0
  
  MaxHTTPConnections 2000
  
  MaxClients 1000
  
  MaxBandwidth 100000
  
  #CustomLog –
  
  
  
  ########################################
  
  ##  static file for testing
  
  ########################################
  
  #HTTP requests
  
  <stream>
  
  File "/home/username/media.flv"
  
  Format flv
  
  </stream>
  
  
  
  #RTSP requests
  
  <stream>
  
  #preconverted file:
  
  File "/home/username/media.mpg"
  
  Format rtp
  
  VideoFrameRate 30
  
  VideoCodec libx264
  
  VideoSize 720x720
  
  StartSendOnKey
  
  Preroll 0
  
  </stream>
  
  
  
  ##################################################
  
  ## usb cam
  
  ###################################################
  
  <feed>
  
  File /tmp/test.ffm
  
  FileMaxSize 20K
  
  ACL allow 192.168.1.149
  
  </feed>
  
  
  
  <stream>
  
  Feed test.ffm
  
  Format rtp
  
  VideoFrameRate 25
  
  VideoCodec libx264
  
  VideoSize 720x720
  
  PreRoll 0
  
  StartSendOnKey
  
  </stream>

  my ffmpeg cmd is

  ffmpeg -s 720x720 -f video4linux2 -i /dev/video0 -r 25 -f alsa -i hw:0 -c:v libx264 -c:a aac -strict -2 rtp://192.168.1.149:1234/test.ffm

  it seems working but showing this error :

  "Data doesn’t look like RTP packets, make sure the RTP muxer is used"

  when i stream the static files it works
  but when i try to play usbcam stream throw ffplay and vlc nothing works

  thank you in advance,