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

Jonathan Campbell jonathan at castus.tv
Sat Sep 7 21:02:19 CEST 2013

> The way I understand this, this means that a file that contains
> the same AC-3 data over and over will then generate a constantly
> repeating noise pattern.
> That sounds like it might be worse than just switching of noise
> generation, at least in some cases.
> If possible it should at least get a frame number as input, then
> it is at least possible to avoid that two consecutive frames generate
> exactly the same noise, though admittedly an application might have a hard
> time always knowing the exact frame number.
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?

For as long as I've had the hack I've not been able to hear any audible 
difference for any AC-3 bitstreams I've played so far, other than being 
able to play the stream backwards with the test program without 
discontinuities in the audio. This includes various AC-3 streams 
extracted from DVD's that I own.

A frame number and an option to turn off noise generation is a good 
idea, I'll add that.

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