Read useful information from a MP4 data stream

streamPeek.js

/*
 * this code examines a MP4 data stream.
 * it looks at the appropriate atoms to determine width, height, and frame rate.
 *
 * It is a sleazy approach, the equivalent of grepping for necessary
 * boxes rather than using box lengths to parse the file.
 */

function read32( buff, fourcc, offset ) {
  let start = 0;
  for( let i = 0; i < fourcc.length; i++ ) {
    start = buff.indexOf( new Buffer( fourcc[i] ), start ) + 4;
  }
  return buff.readUInt32BE( start + offset, 4 );
}

function readfourcc( buff, fourcc, offset ) {
  let start = 0;
  for( let i = 0; i < fourcc.length; i++ ) {
    start = buff.indexOf( new Buffer( fourcc[i] ), start ) + 4;
  }
  return buff.toString( 'ascii', start + offset, start + offset + 4 );
}

function read16( buff, fourcc, offset ) {
  let start = 0;
  for( let i = 0; i < fourcc.length; i++ ) {
    start = buff.indexOf( new Buffer( fourcc[i] ), start ) + 4;
  }
  return buff.readUInt16BE( start + offset, 2 );
}

function streamPeek( buff ) {
  let result = { format: '?', framerate: 0, width: 0, height: 0 };

  try {
    let format = readfourcc( buff, ['ftyp'], 0 );
    if( format === 'mp42' ) {
      let timescale    = read32( buff, ['moov', 'mvhd'], 12 );
      let framescale   = read32( buff, ['moov', 'trak', 'mdhd'], 12 );
      let framerate    = framescale / timescale;
      let width        = read16( buff, ['moov', 'trak', 'stbl', 'avc1'], 24 );
      let height       = read16( buff, ['moov', 'trak', 'stbl', 'avc1'], 26 );
      result.format    = format;
      result.framerate = framerate;
      result.width     = width;
      result.height    = height;
    }
  }
  catch( e ) {
    /* empty */
  }
  return result;
}

  /* sample use */
  const fs = require( 'fs' );
  let buff = new Buffer( 600 );
  fs.open( file, 'r', function( err, fd ) {
    fs.read( fd, buff, 0, buff.length, 0, function( err, bytesRead, buffer ) {
      let str = streamPeek( buffer );
      console.log( str );
    } );
  } );

Thanks to Cameron Kelliher https://gist.github.com/Elements-/cf063254730cd754599e