Quiet Voices on mp4 Video Files
#1
Hello,

This is odd. The voices on mp4 video files are very low compared to the music playing. I only notice it on the files when played through xbmc (on two different machines). It only seems to be that the voices in the movies are much lower than the surrounding music. It works fine in VLC on a different box. The file format is mp4, AVC1, aac 5.1. Both video files I am working with that have this issue are in that format. All other formats seem just fine. I just upgraded xbmc from the SVN two days ago. I am not sure if this problem existed under the old version.

Thoughts?

Thanks in advance,
Jon
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#2
what are you outputting to? perhaps you are outputting 5.1 and have no centre speaker?
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#3
I do think that is the problem, as I am only 2 channel audio on both systems. However, through vlc on a PC, the file downsamples to 2 channel just fine. Do I need to tell xbmc to feed the 5.1 source down to just the 2 channel stereo? If so, where/how?
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#4
Under "Settings", "System Settings", I made sure "downmix multichannel audio to stereo" was selected. It doesn't seem to make a difference.
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#5
I opened it in MoviePlayer and VLC on the same machine, and it is fine. Any thoughts on why the problem only appears in xbmc? What is xbmc running the audio through?
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#6
I just noticed this too.
Was playing the movie 'Happy Feet' for my daughter, which is an MP4 containing 720p AVC1 video and AAC 5.1 audio. The sound dialog interprets the audio channel as "Undetermined - 5.1" and my AV receiver plays 2.1 channel PCM 48 KHz while connected via HDMI (passthrough). The center channel as well as the rear surround channels seem to be missing, hence no voices are heard.

I'd very much like to hear if anyone knows a solution. I am running XBMC 9.11 Camelot on Ubuntu 9.10 karmic 32-bit.
Asus P5N7A-VM + E8400
Ubuntu 9.10 32-bit
XBMC 9.11
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#7
I have the same issue on anything that has AAC 5.1 audio. I also get the "Undetermined - 5.1" listing for the audio source.
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#8
Does your receiver (box powering your speakers) have an option to downmix to stereo? My Onkyo 606 has an option called "All Channel Stereo" which splits the 5 channels between the 2 speakers.
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#9
Hi

I've been trying out xbmc for about a week now.
Outputting analog to an 2-channel amp , my 5.1 aac video files gets the centerchannel mapped to the (front) right speaker. As i'm new to xbmc i dont know if this is new behavior. Mplayer plays the audio fine.
Other than this though i'm having troubles finding faults, what a great mediaplayer Smile

ken
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#10
I'm also have a problem playing AVC+AAC 5.1 - center channel is playing in left rear speaker.
KMPlayer plays same file without problem.

Hardware:
Athlon II X3 425 / Integrated Sound / 5.1 Sound System

Software:
XBMC 9.11 Camelot
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#11
I fought this same problem all day yesterday and here is what we found out. You cannot encode MP4 with AAC and get multi-channel sound, you must encode in MKV with AC3! The MP4 container just doesn't seem to handle multi-channel AAC well or at all, the result usually is low voice (center channel) volume compared to the other channels and no surround sound even though the MP4 will report 5.1 audio. If you use RIPBOT264 you cannot choose AC3 when using MP4 containers. I will end up re-encoding all my old HD-DVD's as MKV with AC3 audio stream and 5.1 channel sound will return (already tested this on a small DVD rip). It also down mixes to stereo just fine.

I don't know if this is an XBMC issue or just an issue with MP4 in general. As much as I dislike MKV it was the only viable option.

Believe it when I say that I did not want to re-encode, but I had no other choice if I wanted normal volumes and 5.1 sound. An HD encode is about 4 hours on my Core i7. To convert the MP4 to MKV using Super and simply copying the streams. Then demux the audio and subtitles from the original source with UsEac3To. Followed by converting the subs with BDSup2Sub. Finally remuxing everything back together with mkvmerge too just as long or maybe longer.

Now if I only want one audio stream (usually just English 5.1) I will just use RipBot264 save as MKV and don't need anything else. If I need other audio streams I have to use other tools. For example:

Huo Yuan Jia ripped single pass with RipBot264 as MP4 only ENG or CHI not both. No 5.1 despite selecting 5.1 AAC-LC or AAC-HE, low voice volumes. Total time to rip about 4.5 hours final file size 4.6 GB.

Same movie ripped single pass with RipBot264 as MKV with no audio. ENG and CHI streams demuxed from disk with UsEac3To along with subs. Subs converted to VOBSubs with BDSup2Sub. Everything remuxed with mkvmerge GUI, total time was about 4.7 hours with a final file size of 5.4 GB. Everything working, 5.1 sound, down mix to stereo, English or Chinese audio, your choice of subtitles, and chapters returned.

The reason this was important to me is that I am running two XBMC boxes on separate TVs pulling the same source from a FreeNAS box. When I started I was using and testing everything on my smaller set and just using the TV speakers. When I finally got around to testing it upstairs on a 7.1 receiver, XBMC always reported 6 channel sound, but my receiver always played stereo sound. It wasn't until I tried the same source on Windows Media Center and Media Center Classic Home Cinema that I realized the source was the problem not XBMC.

I know this information might not sit well with those that have large collections already ripped and encoded as MP4 but I am in the same boat and have reconciled myself to the fact that I am going to have to re-encode. I have spent the better part of this weekend re-ripping HD-DVD and Blu-Ray disks to my local machine for batch encoding later in the week.
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#12
I also have this problem, it does not matter if I output 5.1 or stereo voices tend to come out of the left channel in stereo or the center/left/rear left in 5.1.

VLC plays the file perfectly in stereo and 5.1, of course for 5.1 you need a soundcard that can convert AAC to AC3 or DTS before it reaches the processor/receiver and my soundcard does (using DTS Connect or Dolby Digital Live).

There is something wrong with the way XBMC is reading the AAC track, I have tried all of the output settings in XBMC with no luck.

I also have videos with 5.1 FLAC and the voices come out of the center channel in 5.1 or both channels in stereo like they should.

The only option would be to use MKVExtract and convert the files to AC3 or some other format that XBMC can play properly and then use MKVMerge to re-encode the file.. Huh

Oh yeah, just to let you know it is not MP4 files I am having the problem with but I think it is still relevant.

Edit: Just tried the latest nightly from here: http://www.sshcs.com/xbmc/ and now it works just fine! Awesome!
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#13
Thumbs Up 
I was getting crashes and errors with the nightlies above..

These seem to work properly with AAC and with 5.1 voices come from the center channel as they should, but any version after xbmc-r26540-trunk.exe seems to have problems with my theme (Rapier).

All of those nightlies have a weird bug where if you use alt-tab to go to another application the keyboard won't respond in XBMC anymore requiring you to restart XBMC, although if you just hit the start key on the keyboard and use the start bar to go to another application that does not seem to bother it.

Anyway, I'm glad that the next official version should have this bug worked out since the nightlies seem to. Big Grin
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#14
I'm having this problem as well. I haven't tried the nightlies yet but I can say this isn't a wrapper issue, I remuxed the MP4 into MKV and I'm still getting the same problem - it appears to be an issue with AAC 5.1 and not a specific wrapper. Tbob hit the nail on the head. You've got to open the wrapper, rip out the audio, reencode the auto to AC3, and then rewrap with mkvmerge or whatever. For those of you who are newbies and to encoding / reencoding this guide is pretty solid http://www.kombitz.com/2009/02/24/how-to...-mkv-file/
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