[FFmpeg-devel] Deterministic Noise Generation option for audio codecs that involve noise generation (RNG)

Jonathan Campbell jonathan at castus.tv
Sun Sep 8 10:13:10 CEST 2013

>> Huh, what exactly would motivate an AC-3 decoder to generate the exact same frame data over and over again, other than pure silence, which would not involve any noise coding anyway?
> Maybe none of the AC3 encoders would do this, but many speech codecs have a "comfort noise" mode, where they do exactly encode that: a frame with silence but a bit of generated noise.
> So maybe it's overkill of AC3 but as an API it would be nice if it worked well for these cases, too.
However Michael on this list already brought up using the frame number 
as part of the seed, which is what my patch includes now. Even if the 
frames had the exact same data, the frame number would change the seed 
once per frame, yet the noise pattern will be consistent given the same 
frame data and frame numbers.

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