whammy.js

/*
	var vid = new Whammy.Video();
	vid.add(canvas or data url)
	vid.compile()
*/
module.exports = (function () {
  // in this case, frames has a very specific meaning, which will be 
  // detailed once i finish writing the code

  function toWebM(frames, outputAsArray) {
    var info = checkFrames(frames);

    //max duration by cluster in milliseconds
    var CLUSTER_MAX_DURATION = 30000;

    var EBML = [{
        "id": 0x1a45dfa3, // EBML
        "data": [{
            "data": 1,
            "id": 0x4286 // EBMLVersion
          }, {
            "data": 1,
            "id": 0x42f7 // EBMLReadVersion
          }, {
            "data": 4,
            "id": 0x42f2 // EBMLMaxIDLength
          }, {
            "data": 8,
            "id": 0x42f3 // EBMLMaxSizeLength
          }, {
            "data": "webm",
            "id": 0x4282 // DocType
          }, {
            "data": 2,
            "id": 0x4287 // DocTypeVersion
          }, {
            "data": 2,
            "id": 0x4285 // DocTypeReadVersion
          }
        ]
      }, {
        "id": 0x18538067, // Segment
        "data": [{
            "id": 0x1549a966, // Info
            "data": [{
                "data": 1e6, //do things in millisecs (num of nanosecs for duration scale)
                "id": 0x2ad7b1 // TimecodeScale
              }, {
                "data": "whammy",
                "id": 0x4d80 // MuxingApp
              }, {
                "data": "whammy",
                "id": 0x5741 // WritingApp
              }, {
                "data": doubleToString(info.duration),
                "id": 0x4489 // Duration
              }
            ]
          }, {
            "id": 0x1654ae6b, // Tracks
            "data": [{
                "id": 0xae, // TrackEntry
                "data": [{
                    "data": 1,
                    "id": 0xd7 // TrackNumber
                  }, {
                    "data": 1,
                    "id": 0x63c5 // TrackUID
                  }, {
                    "data": 0,
                    "id": 0x9c // FlagLacing
                  }, {
                    "data": "und",
                    "id": 0x22b59c // Language
                  }, {
                    "data": "V_VP8",
                    "id": 0x86 // CodecID
                  }, {
                    "data": "VP8",
                    "id": 0x258688 // CodecName
                  }, {
                    "data": 1,
                    "id": 0x83 // TrackType
                  }, {
                    "id": 0xe0, // Video
                    "data": [{
                        "data": info.width,
                        "id": 0xb0 // PixelWidth
                      }, {
                        "data": info.height,
                        "id": 0xba // PixelHeight
                      }
                    ]
                  }
                ]
              }
            ]
          },

          //cluster insertion point
        ]
      }
    ];


    //Generate clusters (max duration)
    var frameNumber = 0;
    var clusterTimecode = 0;
    while (frameNumber < frames.length) {

      var clusterFrames = [];
      var clusterDuration = 0;
      do {
        clusterFrames.push(frames[frameNumber]);
        clusterDuration += frames[frameNumber].duration;
        frameNumber++;
      } while (frameNumber < frames.length && clusterDuration < CLUSTER_MAX_DURATION);

      var clusterCounter = 0;
      var cluster = {
        "id": 0x1f43b675, // Cluster
        "data": [{
            "data": clusterTimecode,
            "id": 0xe7 // Timecode
          }
        ].concat(clusterFrames.map(function (webp) {
          var block = makeSimpleBlock({
            discardable: 0,
            frame: webp.data.slice(4),
            invisible: 0,
            keyframe: 1,
            lacing: 0,
            trackNum: 1,
            timecode: Math.round(clusterCounter)
          });
          clusterCounter += webp.duration;
          return {
            data: block,
            id: 0xa3
          };
        }))
      }

      //Add cluster to segment
      EBML[1].data.push(cluster);
      clusterTimecode += clusterDuration;
    }

    return generateEBML(EBML, outputAsArray)
  }

  // sums the lengths of all the frames and gets the duration, woo

  function checkFrames(frames) {
    var width = frames[0].width,
      height = frames[0].height,
      duration = frames[0].duration;
    for (var i = 1; i < frames.length; i++) {
      if (frames[i].width != width) throw "Frame " + (i + 1) + " has a different width";
      if (frames[i].height != height) throw "Frame " + (i + 1) + " has a different height";
      if (frames[i].duration < 0 || frames[i].duration > 0x7fff) throw "Frame " + (i + 1) + " has a weird duration (must be between 0 and 32767)";
      duration += frames[i].duration;
    }
    return {
      duration: duration,
      width: width,
      height: height
    };
  }


  function numToBuffer(num) {
    var parts = [];
    while (num > 0) {
      parts.push(num & 0xff)
      num = num >> 8
    }
    return new Uint8Array(parts.reverse());
  }

  function strToBuffer(str) {
    // return new Blob([str]);

    var arr = new Uint8Array(str.length);
    for (var i = 0; i < str.length; i++) {
      arr[i] = str.charCodeAt(i)
    }
    return arr;
    // this is slower
    // return new Uint8Array(str.split('').map(function(e){
    // 	return e.charCodeAt(0)
    // }))
  }


  //sorry this is ugly, and sort of hard to understand exactly why this was done
  // at all really, but the reason is that there's some code below that i dont really
  // feel like understanding, and this is easier than using my brain.

  function bitsToBuffer(bits) {
    var data = [];
    var pad = (bits.length % 8) ? (new Array(1 + 8 - (bits.length % 8))).join('0') : '';
    bits = pad + bits;
    for (var i = 0; i < bits.length; i += 8) {
      data.push(parseInt(bits.substr(i, 8), 2))
    }
    return new Uint8Array(data);
  }

  function generateEBML(json, outputAsArray) {
    var ebml = [];
    for (var i = 0; i < json.length; i++) {
      var data = json[i].data;
      if (typeof data == 'object') data = generateEBML(data, outputAsArray);
      if (typeof data == 'number') data = bitsToBuffer(data.toString(2));
      if (typeof data == 'string') data = strToBuffer(data);

      if (data.length) {
        var z = z;
      }

      var len = data.size || data.byteLength || data.length;
      var zeroes = Math.ceil(Math.ceil(Math.log(len) / Math.log(2)) / 8);
      var size_str = len.toString(2);
      var padded = (new Array((zeroes * 7 + 7 + 1) - size_str.length)).join('0') + size_str;
      var size = (new Array(zeroes)).join('0') + '1' + padded;

      //i actually dont quite understand what went on up there, so I'm not really
      //going to fix this, i'm probably just going to write some hacky thing which
      //converts that string into a buffer-esque thing

      ebml.push(numToBuffer(json[i].id));
      ebml.push(bitsToBuffer(size));
      ebml.push(data)


    }

    //output as blob or byteArray
    if (outputAsArray) {
      //convert ebml to an array
      var buffer = toFlatArray(ebml)
      return new Uint8Array(buffer);
    } else {
      return new Blob(ebml, {
        type: "video/webm"
      });
    }
  }

  function toFlatArray(arr, outBuffer) {
    if (outBuffer == null) {
      outBuffer = [];
    }
    for (var i = 0; i < arr.length; i++) {
      if (typeof arr[i] == 'object') {
        //an array
        toFlatArray(arr[i], outBuffer)
      } else {
        //a simple element
        outBuffer.push(arr[i]);
      }
    }
    return outBuffer;
  }

  //OKAY, so the following two functions are the string-based old stuff, the reason they're
  //still sort of in here, is that they're actually faster than the new blob stuff because
  //getAsFile isn't widely implemented, or at least, it doesn't work in chrome, which is the
  // only browser which supports get as webp

  //Converting between a string of 0010101001's and binary back and forth is probably inefficient
  //TODO: get rid of this function

  function toBinStr_old(bits) {
    var data = '';
    var pad = (bits.length % 8) ? (new Array(1 + 8 - (bits.length % 8))).join('0') : '';
    bits = pad + bits;
    for (var i = 0; i < bits.length; i += 8) {
      data += String.fromCharCode(parseInt(bits.substr(i, 8), 2))
    }
    return data;
  }

  function generateEBML_old(json) {
    var ebml = '';
    for (var i = 0; i < json.length; i++) {
      var data = json[i].data;
      if (typeof data == 'object') data = generateEBML_old(data);
      if (typeof data == 'number') data = toBinStr_old(data.toString(2));

      var len = data.length;
      var zeroes = Math.ceil(Math.ceil(Math.log(len) / Math.log(2)) / 8);
      var size_str = len.toString(2);
      var padded = (new Array((zeroes * 7 + 7 + 1) - size_str.length)).join('0') + size_str;
      var size = (new Array(zeroes)).join('0') + '1' + padded;

      ebml += toBinStr_old(json[i].id.toString(2)) + toBinStr_old(size) + data;

    }
    return ebml;
  }

  //woot, a function that's actually written for this project!
  //this parses some json markup and makes it into that binary magic
  //which can then get shoved into the matroska comtainer (peaceably)

  function makeSimpleBlock(data) {
    var flags = 0;
    if (data.keyframe) flags |= 128;
    if (data.invisible) flags |= 8;
    if (data.lacing) flags |= (data.lacing << 1);
    if (data.discardable) flags |= 1;
    if (data.trackNum > 127) {
      throw "TrackNumber > 127 not supported";
    }
    var out = [data.trackNum | 0x80, data.timecode >> 8, data.timecode & 0xff, flags].map(function (e) {
      return String.fromCharCode(e)
    }).join('') + data.frame;

    return out;
  }

  // here's something else taken verbatim from weppy, awesome rite?

  function parseWebP(riff) {
    var VP8 = riff.RIFF[0].WEBP[0];

    var frame_start = VP8.indexOf('\x9d\x01\x2a'); //A VP8 keyframe starts with the 0x9d012a header
    for (var i = 0, c = []; i < 4; i++) c[i] = VP8.charCodeAt(frame_start + 3 + i);

    var width, horizontal_scale, height, vertical_scale, tmp;

    //the code below is literally copied verbatim from the bitstream spec
    tmp = (c[1] << 8) | c[0];
    width = tmp & 0x3FFF;
    horizontal_scale = tmp >> 14;
    tmp = (c[3] << 8) | c[2];
    height = tmp & 0x3FFF;
    vertical_scale = tmp >> 14;
    return {
      width: width,
      height: height,
      data: VP8,
      riff: riff
    }
  }

  // i think i'm going off on a riff by pretending this is some known
  // idiom which i'm making a casual and brilliant pun about, but since
  // i can't find anything on google which conforms to this idiomatic
  // usage, I'm assuming this is just a consequence of some psychotic
  // break which makes me make up puns. well, enough riff-raff (aha a
  // rescue of sorts), this function was ripped wholesale from weppy

  function parseRIFF(string) {
    var offset = 0;
    var chunks = {};

    while (offset < string.length) {
      var id = string.substr(offset, 4);
      var len = parseInt(string.substr(offset + 4, 4).split('').map(function (i) {
        var unpadded = i.charCodeAt(0).toString(2);
        return (new Array(8 - unpadded.length + 1)).join('0') + unpadded
      }).join(''), 2);
      var data = string.substr(offset + 4 + 4, len);
      offset += 4 + 4 + len;
      chunks[id] = chunks[id] || [];

      if (id == 'RIFF' || id == 'LIST') {
        chunks[id].push(parseRIFF(data));
      } else {
        chunks[id].push(data);
      }
    }
    return chunks;
  }

  // here's a little utility function that acts as a utility for other functions
  // basically, the only purpose is for encoding "Duration", which is encoded as
  // a double (considerably more difficult to encode than an integer)

  function doubleToString(num) {
    return [].slice.call(
    new Uint8Array(
    (
    new Float64Array([num]) //create a float64 array
    ).buffer) //extract the array buffer
    , 0) // convert the Uint8Array into a regular array
    .map(function (e) { //since it's a regular array, we can now use map
      return String.fromCharCode(e) // encode all the bytes individually
    })
      .reverse() //correct the byte endianness (assume it's little endian for now)
    .join('') // join the bytes in holy matrimony as a string
  }

  function WhammyVideo(speed, quality) { // a more abstract-ish API
    this.frames = [];
    this.duration = 1000 / speed;
    this.quality = quality || 0.8;
  }

  WhammyVideo.prototype.add = function (frame, duration) {
    if (typeof duration != 'undefined' && this.duration) throw "you can't pass a duration if the fps is set";
    if (typeof duration == 'undefined' && !this.duration) throw "if you don't have the fps set, you ned to have durations here."
    if ('canvas' in frame) { //CanvasRenderingContext2D
      frame = frame.canvas;
    }
    if ('toDataURL' in frame) {
      frame = frame.toDataURL('image/webp', this.quality)
    } else if (typeof frame != "string") {
      throw "frame must be a a HTMLCanvasElement, a CanvasRenderingContext2D or a DataURI formatted string"
    }
    if (!(/^data:image\/webp;base64,/ig).test(frame)) {
      throw "Input must be formatted properly as a base64 encoded DataURI of type image/webp";
    }
    this.frames.push({
      image: frame,
      duration: duration || this.duration
    })
  }

  WhammyVideo.prototype.compile = function (outputAsArray) {
    return new toWebM(this.frames.map(function (frame) {
      var webp = parseWebP(parseRIFF(atob(frame.image.slice(23))));
      webp.duration = frame.duration;
      return webp;
    }), outputAsArray)
  }

  return {
    Video: WhammyVideo,
    fromImageArray: function (images, fps, outputAsArray) {
      return toWebM(images.map(function (image) {
        var webp = parseWebP(parseRIFF(atob(image.slice(23))))
        webp.duration = 1000 / fps;
        return webp;
      }), outputAsArray)
    },
    toWebM: toWebM
    // expose methods of madness
  }
})()