I have this mpg that uses WMA9 codec 20kbps, 44KHz, mono (A/V) 2-pass CBR. When played through WMP10 there's no sound.

Here's the strange thing, there's sound if it's STEREO but not when it's MONO. Does anyone have an idea as to why there's sound only when it's STEREO and no sound when it's MONO using the WMA9 codec?

It may be due to mono signal going to the Central (Voice) channel, instead of front L and R. Try to demux WMA part and then play it back in the latest fb2k.

Does it mean mpg do not support this setting?

Mpg by standard can't have wma9 sound.

This only happens when I playback the mpg in WMP10, when I play the video in VLC or TCMP there is sound.

What is your configuration for Tools -> Options -> Devices -> Speakers? What is shown about audio in File -> Properties when you play the file?

This is what is shown: WMA9 codec 20kbps, 44KHz, mono (A/V) 2-pass CBR

When I play a file with these audio properites: WMA9 codec 20kbps, 44KHz, stereo (A/V) 2-pass CBR. There is sound. Like I said, there's no sound when it's a monaural source.

What is your configuration for Tools -> Options -> Devices -> Speakers?

DirectSound: SB X-Fi Audio

I mean, what is your speakers configuration? Headphones, 5.1, 7.1?

Sorry, it's 5.1

This is really weird, I tried playing the monaural file again with WMP10 and there's sound now! I tried different settings to see if I could reproduce the problem again but no cigar.

I have no junk programs installed on my computer. I never install codec packs. Everything single program I have on my computer I use frequently.