high CPU with true hd in ffdshow

I have a high CPU when I play a video with true hd audio with libavcodec in ffdshow.
Audio: true-hd, 7.1, 48000 Hz, 9000ko/s.

Whereas with AC3 filter, I have no problem.

There is nothing that can be done about that. ffdshow is not being developed anymore.

You could also try LAV Audio decoder instead. That is likely to become the new default in the future.

I've trying with LAV and the video is slow but it's better than ffdshow.

Audio #1
ID : 4352 (0x1100)
ID de menu : 1 (0x1)
Format : TrueHD / AC-3
Extension du mode : CM (complete main)
Paramètres du format, Endianness : Big
Type de muxing : Stream extension
Identifiant du codec : 131
Durée : 2h 12mn
Type de débit : Variable / Constant
Débit : 640 Kbps
Débit maximum : 6 510 Kbps
Canaux : 8 canaux / 6 canaux
Position des cannaux : Front: L C R, Side: L R, Back: L R, LFE / Front: L C R, Side: L R, LFE
Echantillonnage : 48,0 KHz
Profondeur des couleurs : 16 bits
Taille du flux : 605 Mio (2%)

Can you tell me where you downloaded that file? Then I can get it and do some tests.

How big is the difference in CPU usage?

ffdshow does some extra parsing of the input data to identify the correct audio format, because in the past there were some splitters that wrongly tagged TrueHD and MLP as AC3 audio. But the extra parsing should only account for a small increase in CPU usage.

intel pentium E6300 dual-core 2.8Ghz
NVIDIA GTX275

KLM codec pack 1000
LAV splitter + LAV CUVID + madVR

with LAV audio 25% CPU (VIDEO slow)

Blueray Disc star trek into darkness (for example)

I found, I've disabled dithering 16 bit in LAV audio and this works fine

Thanks for the info. I shall pass it along to the developer of LAV, maybe it can be improved.