according to the IA :

WAS/WASAPI and ASIO do NOT use the same audio decoding engine under Windows.
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🔹 In WAS (WASAPI) mode
When BIAB (or Windows Media Player) is in WAS mode:
• Windows uses:
o Media Foundation
o + the complete Windows media graph
• WMA Pro decoding is performed before the audio output
• Only then:
o the decoded stream is sent to the sound card
➡️ Result:
✅ the WMA file is decoded correctly
✅ playback works
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🔹 In ASIO mode
When you switch to ASIO:
• ASIO completely bypasses the Windows audio stack
• There is:
o ❌ no more media graph
o ❌ no more complete Media Foundation
• BIAB then asks Windows:

"Give me the decoded audio stream"
But:
• Windows can no longer initialize the WMA Pro decoder
• because it depends on the WAS / Media Foundation stack
➡️ Result:
• ❌ decoding Impossible
• ❌ Error: Unsupported format
• ❌ Windows Media Player also fails when ASIO is active

Audio Mode WMA Pro Decoding Playback
WAS / WASAPI ✔️ via Media Foundation ✔️ OK
ASIO ❌ Media Foundation not accessible ❌ Error
VLC ✔️ internal codec ✔️ OK
👉 The format is NOT invalid
👉 The codec path disappears when ASIO takes over
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🔥 Why is this happening now (it used to work)?
Since Windows 10 (22H2) / Windows 11:
• Microsoft has:
o fragmented Media Foundation
o tied certain codecs to the WAS pipeline
• WMA Pro only works within this pipeline
➡️ ASIO = outside the pipeline = unavailable codec

=> use BIAB in WAS mode !