whisper : initialize decoder's rng with unique seed

[danbev]

This change initializes each decoder's random number generator with a unique seed.

The motivation for this is that currently all decoders are initialized with the same seed value, 0. The result of this is that for the same state (logits, probs, and logprobs) they will produce the same output.

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Currently this is what I'm seeing which triggered this pr:

These are the values for j=1:

(lldb) p tokens_new
(const std::vector<whisper_token_data>) size=5 {
  [0] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [1] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [2] = (id = 50365, tid = 50365, p = 0.00626884214, plog = -5.07216358, pt = 0.00626884214, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [3] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [4] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
}

These are the values for j=2:

(lldb) p tokens_new
(const std::vector<whisper_token_data>) size=5 {
  [0] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [1] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [2] = (id = 50365, tid = 50365, p = 0.00626884214, plog = -5.07216358, pt = 0.00626884214, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [3] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [4] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
}

These are the values for j=3:

(lldb) p tokens_new
(const std::vector<whisper_token_data>) size=5 {
  [0] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [1] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [2] = (id = 50365, tid = 50365, p = 0.00626884214, plog = -5.07216358, pt = 0.00626884214, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [3] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [4] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
}

These are the values for j=4:

(lldb) p tokens_new
(const std::vector<whisper_token_data>) size=5 {
  [0] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [1] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [2] = (id = 50365, tid = 50365, p = 0.00626884214, plog = -5.07216358, pt = 0.00626884214, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [3] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
  [4] = (id = 50363, tid = 50363, p = 0.837067842, plog = -0.177850127, pt = 0.837067842, ptsum = 0.985369741, t0 = -1, t1 = -1, t_dtw = -1, vlen = 0)
}

[ggerganov]

Hm, interesting. This will likely have a positive impact on the quality when using beam search.