WEM Opus differs when generated on Intel and AMD x64 CPUs

Question

Hello,

Our workstations are equipped with an Intel or AMD CPU, and the Opus conversion produces different WEMs depending on the CPU (using Wwise 2021.1.7.7796).

The WEMs are stored on Perforce, and we also use a hash mechanism to track updates. The conversion not being deterministic then causes a few troubles.

Would it be possible to add an option in the conversion settings to get deterministic output ?

We made a bit of research and found that the SSE's RCPPS and RSQRTPS instructions were to blame, due to their approximate behavior and different implementation in AMD/Intel microcode. A more portable way to enforce a deterministic output would be to enable fixed point computation in the codec, but it may come at a certain cost. For more details on that, please take a look at the issue I opened on the Opus Github.

Thanks!

 

Answer 1

We are aware of this issue and it will be fixed in the upcoming Wwise 22.1 as "WG-60959: Encoding of WEM Opus media produces slightly different results across AMD and Intel CPUs."

There is no plan to backport this fix to previous versions at the moment due to the impact on all Opus files.
You can always contact Audiokinetic Support if this is blocking you to find a personalized solution.