A little follow up... Ultimately, the problem was that the APO_FLAG_SAMPLESPERFRAME_MUST_MATCH registry flag was being set (since our original code was based off of the swap example, before the speakerfill example was available). Thus, any case where input and output channels counts were different, it wouldn't be called. The information about this flag is documented in AudioEngineBaseApo.idl (not in the word document). I've found that once properly configure, this type of APO can be tested using GraphEdit (available with the Direct X SDK) to play multi-channel wav files. ________________________________ From: wdmaudiodev-bounce@xxxxxxxxxxxxx [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Hakon Strande Sent: Friday, February 02, 2007 3:32 PM To: wdmaudiodev@xxxxxxxxxxxxx Subject: [wdmaudiodev] Re: Multi-channel->2 channel APO on 2-channel device Dear Madam, I think this is covered in the white paper on this subject http://www.microsoft.com/whdc/device/audio/sysfx.mspx but what you are suggesting is possible when you load your APO into the Local Effect (LFX) insertion point (per app) so please check that you are doing that. From a high level the LFX exposed the format that the LFX wants (such as multi-channel) and then down mixes that to a stereo stream for instance. This functionality is already in Vista though... Sincerely, HakonS From: wdmaudiodev-bounce@xxxxxxxxxxxxx [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Alexandra Schoepel (Ally) Sent: Friday, February 02, 2007 1:24 PM To: wdmaudiodev@xxxxxxxxxxxxx Subject: [wdmaudiodev] Multi-channel->2 channel APO on 2-channel device Hi Guys, First off, thanks for all your help over the past few months. It's great to have your support. We are working on an APO that would provide the service of taking a multi-channel surround mix and mixing to 2 channels (with user controls), in the case where the hardware device is a maximum 2-channel output device. I have looked into the InputFormatSupported function and overridden the base functionality. However, I never see a request for more than 2-channels. Even when using the Graph Edit tool with a multi-channel PCM wave file or a WMV HD file containing a 5.1 mix, using the MM system over Dsound, as instructed from a previous posting on this same forum. I assume that this is because, in a traditional sense, the device is being queried for the maximum number of channels. In spite of the APO I have in place which will honor 5.1 channels, the application is told 2 channels and therefore the system arranges for 2 channels down the pipe and I never see a query for anything but that. I hope I'm wrong? So, is it even possible to write an APO providing the functionality described for a 2-channel soundcard? Thanks again, Ally