Roku BIF File JavaScript Parser

gistfile1.js

// Takes an ArrayBuffer; returns an array of these objects:
// {
//    seconds: *number of seconds into the video of this image*,
//    bytes: *the bytes of this image, as an ArrayBuffer* 
// }
var parseBif = function(buffer) {
  var data = new Uint8Array(buffer);

  // Make sure this really is a BIF.
  var magicNumber = [0x89, 0x42, 0x49, 0x46, 0x0d, 0x0a, 0x1a, 0x0a];

  for (var i = 0; i < magicNumber.length; i++) {
    if (data[i] != magicNumber[i]) {
      return false;
    }
  }

  var version = sliceToLong(data, 8, 12);

  if (version != 0) {
    return false;
  }

  var separation = sliceToLong(data, 16, 20);

  if (separation == 0) {
    separation = 1000;
  }

  var refs = [];
  var lastRef = null;

  for (var i = 64; true; i += 8) {
    var ts = sliceToLong(data, i, i + 4);
    var offset = sliceToLong(data, i + 4, i + 8);

    if (ts == 0xFFFFFFFF) {
      lastRef.end = offset;
      break;
    }

    var ref = {
      timestamp: ts,
      start: offset
    };

    if (lastRef != null) {
      lastRef.end = offset;
    }

    refs.push(ref);
    lastRef = ref;
  }

  var images = [];

  for (var i = 0; i < refs.length; i++) {
    var ref = refs[i];

    images.push({
      seconds: (ref.timestamp * separation) / 1000,
      bytes: buffer.slice(ref.start, ref.end)
    });
  }

  return images;
};

var sliceToLong = function(data, start, end) {
  var value = 0;

  for (var i = end - 1; i >= start; i--) {
      value = (value * 256) + data[i];
  }

  return value;
};