If you installed FFDshow along with my codecs, you're asking for trouble because FFDshow is included in my releases. If this is your case I suggest that you uninstall ffdshow, press [Reset All] in the Settings Application, select the [x] SUGGESTED settings checkbox, and then go to the Audio TAB and select the HDMI (bitstream) setting.
AVRs sold in ISDB countries can almost always decode AAC (as AAC is the standard audio format of ISDB). AMD, NVIDIA, Intel can bitstream AAC over HDMI, of course. If you are not living in these countries, perhaps your AVR can't decode AAC.
The topic concerned audio within an MP4. We are not discussing Broadcast signals.
I do not know of any software that would send the AAC audio within an MP4 to the AVR for decoding.
EDIT: i am aware that ffdshow can trascode it on the fly to DD but I do not see the advantage.
BTW, the OP states "Yamaha RX-V665" which does not decode AAC.
I've been using MediaPortal for years and I don't use the Shark or any pack... I do use the MPC-HC and its Stand Alone Filter for decoding .264 files. I also use SPDIFer to pass digital audio in mt HTPC and LAV Audio on my bedroom PC to pass analog audio. One more thing: I use the LAV splitter and the MS-DTV codec for TV and DVD playback. So, in review: MPC Video Codec for VIDEO mpeg2 and .264, MSDTV codec for TV and DVD. Works like a charm and if you have multiple audio streams just toggle them via keyboard or the audio track button on your remote! All of my .264 files have either AC3 or DTS audio and an optional AAC soundtrack - when playing AAC it shows as PCM on my Onkyo. The DTS and AC3 (DD) show up as themselves... I only keep the AAC on my .m4v containers for iPhone ease of playback.
"The OP states "Yamaha RX-V665" which does not decode AAC"
This was another thing I was thinking about. Is there some way to find out exactly what audio format the file has? Maybe some type of program. Again I have searched, but have not really found anything that would do this.
"If you installed FFDshow along with my codecs, you're asking for trouble because FFDshow is included in my releases."
What I have done is followed a setup guide that I found on this site. I believe you are correct and FFDshow was installed through the Shark package. As I stated everything is working great except MP4 video files which I really don't use to often. For the most part I rip my Blu-rays and then play them through MediaPortal and I have no problem with DTS-HD being decoded and played by my receiver. Sounds great. This is probably why I notice the MP4 files not sounding very good.
"I do use the MPC-HC and its Stand Alone Filter for decoding .264 files"
I'll give this a try. Back before using MCE I used MPC-HC and I don't recall having a problem back then. Maybe this is the fix I am looking for, but rather have everything running through default player for MediaPortal and MCE since again I don't play MP4 files very often and I rather not break what is already working for 95% of what I do.
"if you have multiple audio streams just toggle them via keyboard or the audio track button on your remote!"
Did not realize you could do this. Which program exactly does this work for and what is the key combination you hit to do this?
The above gives me a couple things to try, but any more suggestions would be greatly appreciated.
MPC-HC has a SAF you simply download and register. Once MPCVideoDec.ax is registered it's available in the MP config to select. As I stated, I select it for mpeg-2 and .264 for Video playback and along with having the LAV splitter it works GREAT and all from inside MediaPortal. Using their player is just a shortcut to test their codec without registering their SAF and it also has a working splitter inside their player which is needed. Audio toggle is the capitol A key and it's mapped to the 4th button on my MCE remote (Green) as well the other three (Yellow, Blue & Red) toggle things like AR, Subtitles, and such. But that's only a direct shortcut, you can access these menus from the Info page (Info button on MCE remote) during playback as well by using the directional buttons then Enter.
MediaPortal is a really friendly GUI if you get to know it! I use the StreamedMP plugin which adds MyMovies plug-in to database/play all of my movies (whether .iso, .mkv, .m4v, .mp4, .avi), and the TV Server to play LiveTV, record it and play RecordedTV not to mention the TVSeries plugin to present them/playback in a user friendly method! Since I have a CableCard I have to use WMC for those channels, but I use MP for all my OTA and analog cable tuning... it's a wonderful application!
Let me say: your mp4 files may or may not have alternate audio tracks. D/l MediaInfo and have it tell you... in fact, MediaPortal will LOG this (since it uses MediaInfo, internally) when you ask it to play a file - just read the log file! Assuming your "files" have two audio tracks, MediaPortal plays the 1st one as its default and if that's the stereo AAC it will pass as PCM, hit the toggle to pass the other! Viola`
Doing so will allow LAV to decode the audio sending all available channels to the receiver for playback.
Also check Control Panel | Sound for the correct speaker count under your active connection.