Just an FYI for those who fancy the DivX ;-) MPEG4 video craze. I ran into a problem last month in which the audio playback in my DivX movies inexplicably went into the toilet. My original plea for help was here. I've pasted the important parts below for your convenience 
"When I playback DivX (MPEG-4 *.avi) movies, the MP3 audio stream has a stuttering metallic echo (voices have a "gurgling" echo) and the overall sound level is very low. It's happening in both Win98 and Win2k with Media Player 6.4 whereas it used to work perfectly. But they play back fine in Win98 Lite (triple-booting Win98, Win98 Lite, and Win2k). The video is perfect in all three OS's, only the audio is flaky. I have no idea what could be wrong, I haven't installed any audio-related software which [to my knowledge] would have conflicted, and nothing common to both Win98 & Win2k. I've checked the codecs, reinstalled Media Player, checked hardware configuration...basically everything I can imagine that could be related to this sort of problem."
"Here's where it gets really weird. Today I encoded "The Matrix" with FlaskMPEG in Win2k. If I play it back in Win2k, the audio is screwed. But if I boot into Win98 Lite and play it back, everything is fine. Same thing with trailers I downloaded over the 'net, all of which used to play back perfectly. All of my DivX videos are encoded with MP3 audio streams, so I suspected a problem with the MP3 codec. But if I play an MP3 (audio only) in media player, it sounds fine. ARGHHH!"
Well, it turns out playback in 98Lite was messed up as well or at least it evolved into such. And I later discovered it wasn't restricted to MP3 interleaves, but WMA (and presumably all other audio formats) as well. Any A/V interleave format, DVD/MPEG2, AVI, whatever had this problem. Now please understand that the troubleshooting path was very painful; I've installed/uninstalled software, deleted registry entries, wiped DirectX, manipulated IRQ's, etc. more times than I care to admit.
You won't believe what the problem was.
Yesterday I installed a new video card (from Creative Savage4 3D PCI -> ATI AIW Pro AGP) and the problem went away. Ahh, my movies are back, pristine as ever. I could not, and still can not, rationalize how a video card could screw up audio playback...which is why this problem was so hard to trace. Keep in mind that this whole time video display quality was as good as ever. I reinstalled the old card again just to be sure, and yes the problem reappeared. I initially thought it must have been an artifact of [poorly-implimented] IRQ sharing between the sound and video cards. But the sound card is a Soundblaster 16 ISA on a dedicated IRQ. Not to mention the old PCI video and the new AGP video use the same IRQ. I'm left thinking it must be a driver issue with the Creative PCI video. I was using the most recent reference drivers, if I have some time to burn maybe I'll try an older driver release. I'm quite sure it isn't something inherent of PCI video cards in general, but I had an AGP card prior to both of these in which everything worked well. I'd be interested to know if anyone has a Creative Savage PCI video card working properly with A/V playback.
I just wanted to share this peculiar experience with you guys in the off-chance it will save you some grief in the future. Now if anybody knows why this happened, why don't you just tell me what the hell was happening!
Best regards,
Floyd
"When I playback DivX (MPEG-4 *.avi) movies, the MP3 audio stream has a stuttering metallic echo (voices have a "gurgling" echo) and the overall sound level is very low. It's happening in both Win98 and Win2k with Media Player 6.4 whereas it used to work perfectly. But they play back fine in Win98 Lite (triple-booting Win98, Win98 Lite, and Win2k). The video is perfect in all three OS's, only the audio is flaky. I have no idea what could be wrong, I haven't installed any audio-related software which [to my knowledge] would have conflicted, and nothing common to both Win98 & Win2k. I've checked the codecs, reinstalled Media Player, checked hardware configuration...basically everything I can imagine that could be related to this sort of problem."
"Here's where it gets really weird. Today I encoded "The Matrix" with FlaskMPEG in Win2k. If I play it back in Win2k, the audio is screwed. But if I boot into Win98 Lite and play it back, everything is fine. Same thing with trailers I downloaded over the 'net, all of which used to play back perfectly. All of my DivX videos are encoded with MP3 audio streams, so I suspected a problem with the MP3 codec. But if I play an MP3 (audio only) in media player, it sounds fine. ARGHHH!"
Well, it turns out playback in 98Lite was messed up as well or at least it evolved into such. And I later discovered it wasn't restricted to MP3 interleaves, but WMA (and presumably all other audio formats) as well. Any A/V interleave format, DVD/MPEG2, AVI, whatever had this problem. Now please understand that the troubleshooting path was very painful; I've installed/uninstalled software, deleted registry entries, wiped DirectX, manipulated IRQ's, etc. more times than I care to admit.
You won't believe what the problem was.
Yesterday I installed a new video card (from Creative Savage4 3D PCI -> ATI AIW Pro AGP) and the problem went away. Ahh, my movies are back, pristine as ever. I could not, and still can not, rationalize how a video card could screw up audio playback...which is why this problem was so hard to trace. Keep in mind that this whole time video display quality was as good as ever. I reinstalled the old card again just to be sure, and yes the problem reappeared. I initially thought it must have been an artifact of [poorly-implimented] IRQ sharing between the sound and video cards. But the sound card is a Soundblaster 16 ISA on a dedicated IRQ. Not to mention the old PCI video and the new AGP video use the same IRQ. I'm left thinking it must be a driver issue with the Creative PCI video. I was using the most recent reference drivers, if I have some time to burn maybe I'll try an older driver release. I'm quite sure it isn't something inherent of PCI video cards in general, but I had an AGP card prior to both of these in which everything worked well. I'd be interested to know if anyone has a Creative Savage PCI video card working properly with A/V playback.
I just wanted to share this peculiar experience with you guys in the off-chance it will save you some grief in the future. Now if anybody knows why this happened, why don't you just tell me what the hell was happening!
Best regards,
Floyd
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