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• Need help on handling MPEG4V1 data

  31 janvier 2021, par Gediminas

  I'm in situation where I need to get a chunk of MPEG4V1 (Microsoft MPEG-4 VKI
Codec V1) data located in the beginning of a packet (that was sent by some DVR unit).

  



  Packet structure looks something like this :

  



  

  • Compressed MPEG4 data.

  


  • Long integer - Number of events and tripwires.

  


  • Long integer - Number of events.

  


  • Event - Event's sequence.

  


  • Long integer - Number of tripwires.

  


  • Tripwire - Tripwires sequence.

  


  • Long integer - Cyclical redundant code (CRC).

  


  



  So there is no indication of how to know where does the MPEG4 data ends (Or is there ?),
and from where should I start reading this additional data like "Number of events and tripwires" and etc...

  



  I uploaded two packet's so you could see how the actual data looks like :
recvData1.txt,
recvData2.txt.

  



  I've tried to decode those packets using FFmpeg library with avcodec_decode_video function and by removing byte by byte from the end of my recvData buffer in a hope for any results,
  
but FFmpeg just allways returned with an error messages like this :

  



  


  "[msmpeg4v1 @ 038865a0] invalid startcode",
 "[msmpeg4v1 @ 038865a0] header damaged".

  


  



  I'm not that good specialist on knowing of how does the MPEG4 works from the inside,
but judging by the error messages it's clearly seen that I'm missing some data for decoding at the start of the buffer.

  



  So I'm not sure of what part / kind of MPEG data I'm getting here..
  
Maybe it's some kind of MPEG's "frame" data with it's "end" indication or something ?

  



  I've even compared the start of my recvData buffer to some of MPEG4V1 encoded video files I found on the net "http://www.trekmania.net/clips/video_clips4.htm" to check if the start of my buffer really contains the MPEG data ..and not some kind of DVR vendor specific stuff..

  



  And I noticed that there are about 20bytes of data 
(at the start of my packet data, and in .avi files right after about 180bytes..) 
that looks like some kind of header or something..

  



  Please check this image : "http://ggodis.gamedev.lt/stackOverflow/recvData.jpg"

  



  Maybe someone knows what this part of MPEG4V1 data represents ?

  



  P.S. ..I've checked the CRC values for my received packets and they were correct..

  


• Error : ffmpeg exited with code 2 - Docker Container

  15 avril 2020, par Vincenzo Asta

  I created a Docker Container that when I run I get this error (Why do I get this error ? It works locally) :

  



  {&#xA;    "message": "Error: ffmpeg exited with code 2&#xA;    at ChildProcess.<anonymous> (/app/lib/node_modules/fluent-ffmpeg/lib/processor.js:182:22)&#xA;    at emitTwo (events.js:126:13)&#xA;    at ChildProcess.emit (events.js:214:7)&#xA;    at Process.ChildProcess._handle.onexit (internal/child_process.js:198:12)"&#xA;}&#xA;</anonymous>

  



  Below, the part of code where I get the error (in particular the execution goes into reject) :

  



  var ffmpeg = require('fluent-ffmpeg');

module.exports = (sourcePath, outputPath, af, outputFormat="mp3") => {
    return new Promise((resolve, reject) => {
        let proc = new ffmpeg({ source: sourcePath, nolog: true });
        proc.audioQuality(0);
        proc.audioFilters(af);
        proc.setFfmpegPath(__dirname + "/ffmpeg-20180325-5b31dd1-win64-static/bin/ffmpeg.exe");
        proc.toFormat(outputFormat).on('end', function () {
            resolve();
        })
        .on('error', function (err) {
            reject(err);
        })
            .saveToFile(outputPath);
    })
}


  



  My Dockerfile :

  



  FROM node:8.11.1

WORKDIR /app

COPY package*.json /app/

RUN npm install

COPY . /app/

EXPOSE 8000

CMD [ "node", "app.js" ]


  



  My package.json :

  



  {
  "name": "",
  "version": "1.0.0",
  "description": "",
  "main": "app.js",
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.16.4",
    "azure-storage": "^2.1.0",
    "crypto": "^0.0.3",
    "ffmpeg": "^0.0.4",
    "ffmpeg-normalize": "^1.3.0",
    "fluent-ffmpeg": "^2.1.2",
    "fs": "^0.0.1-security",
    "jmespath": "0.15.0",
    "mp3-duration": "^1.1.0",
    "striptags": "^3.1.1"
  }
}


  


• Cortex-A7 instruction cycle timings

  15 mai 2014, par Mans — ARM

  The Cortex-A7 ARM core is a popular choice in low-power and low-cost designs. Unfortunately, the public TRM does not include instruction timing information. It does reveal that execution is in-order which makes measuring the throughput and latency for individual instructions relatively straight-forward. The table below lists the measured issue cycles … Continue reading →