Add timestamp support

[azihassan]

Some youtube links have a t parameter that makes the player jump to a given timestamp in the video. Not sure how this is implemented, but I'm guessing it might have something to do with the range parameter. It's worth looking into it.

[azihassan]

I compared a video URL at different timestamps, but only the range, rn and lsig fields changed. mt refers to the current timestamp, but I think range is the only relevant piece :

[azihassan]

The total video length in bytes is 38076857. It's 722 seconds long. Using that information, I tried to deduce the range for timestamp 5:25 (325 seconds) with the 38076857 * 325 / 722 formula, but it resulted in a different range (17139859.452908587)

[azihassan]

I added a break point to the mouse click and XHR events and eventually ended up in this part of the code :

  g.k.zB = function (a, b, c) {
    for (var d = [], e = a; e <= this.index.wd(); e++) {
      var f = GE(this.index.Vp(e), fva(this.index, e)),
        h = this.index.getStartTime(e),
        l = this.index.getDuration(e),
        m = Math.max(0, b - f.start),
        n = Math.min(f.end + 1, b + c) - (f.start + m);
      d.push(new IE(3, this, f, "getRequestInfoForRange", e, h, l, m, n));
      if (f.start + m + n >= b + c) break;
    }
    d.length || g.lB(new g.qx("b189619593", "" + a, "" + b, "" + c));
    return new RE(d);
  };

It looks like this is where offsets are calculated. Here's a screenshot of the debugger after I clicked on the 7:51 minute mark. I found a video URL in the network tab where the start field was mentioned in the range query parameter, but I forgot to copy it :

[azihassan]

Definition of the IE object :

  IE = function (a, b, c, d, e, f, h, l, m, n) {
    d = void 0 === d ? "" : d;
    this.type = a;
    this.j = b;
    this.range = c;
    this.source = d;
    this.J = [];
    this.D = "";
    this.Oa = -1;
    this.D = d;
    this.Oa = 0 <= e ? e : -1;
    this.startTime = f || 0;
    this.duration = h || 0;
    this.Qb = l || 0;
    this.u = 0 <= m ? m : this.range ? this.range.length : NaN;
    this.sf = this.range
      ? this.Qb + this.u === this.range.length
      : void 0 === n
      ? !!this.u
      : n;
    this.range
      ? ((this.B =
          this.startTime + (this.duration * this.Qb) / this.range.length),
        (this.I = (this.duration * this.u) / this.range.length),
        (this.C = this.B + this.I))
      : xua(this);
  };

[azihassan]

The total video length in bytes is 38076857. It's 722 seconds long. Using that information, I tried to deduce the range for timestamp 5:25 (325 seconds) with the 38076857 * 325 / 722 formula, but it resulted in a different range (17139859.452908587)

This doesn't take into account the bitrate. A more accurate range can be found by multiplying the bitrate and time offset :

range = bitrate * t * 1024 / 8

The bitrate is available in the formats and adaptiveFormats arrays. Not sure if it's a constant bitrate or if it's the average of the variable bitrates though.