AC3 6ch audio strange behavior in AVISynth

[lovyagin]

I've suddenly got a weird problem with 6ch ac3 audio in AVISynth. No matter if it is muxed to mkv or placed as separate ac3 file AVISynth (aka directshowsource) doesn't output it as 6ch, exporting 2ch (stereo) but it occured so not as downmixed, but as slowed down (probably 3 times) in speed! Same time in Media Player Classic it is playable well (normal speed, 6ch). I've tried to find if there is a DS/ACM filter that trying to downmix it but I've not find such one (I have ffdshow, ac3acm, ac3filter at least, any downmix isn't configured in their settings).

Please, help!!!

[jagabo]

Open your source file with GSpot. Press the little "1" button near the bottom under MS A/V. To the right you will see a list of filters that that DirectShow will use to play the file. You should see the AC3 decoder listed there.

[lovyagin]

GSpot says it uses AC3filter. In its properties no downmix set (AS IS). In GSpot (as well in MPC) it is playable properly. Only AViSynth result that slowdown.

[jagabo]

Does AviSynth's Info() show the correct audio parameters?

[lovyagin]

Everything shown is correct expect number of channel, it is shown 2 instead of 6.

[jagabo]

I don't think AviSynth can handle six channels. Audio has to be downmixed to 2 channels. I don't know why it would come out at 1/3 speed. Why don't you just ignore the audio in AviSynth (DirectshowSource("filename.ext", audio=false)) and mux the original AC3 audio separately?

[poisondeathray]

Use NICAC3Source() if you want more consistency and audio separately (assuming you want to re-encode, not copy) , or FFMpegSource2("video.mkv",atrack=-1) if together in .mkv

I know you said you checked it, but you must have a downmix somewhere (I'm guessing either AC3Filter or FFDShow)

[jagabo]

If you want downmixed audio try disabling AC3Filter. See if ffdshow does any better.

[lovyagin]

Thanks a lot for suggestions!

I don't think AviSynth can handle six channels.

Maybe this is the reason... but... I do remember that I converted 6ch audio using avisynth, but probably it was AAC not AC3 I do not remember.

Audio has to be downmixed to 2 channels. I don't know why it would come out at 1/3 speed.

Seems to me it is converted to 6ch RAW (PCM) somewhere but played as 2 ch. So, probably only header came from AVISynth is incorrect? Is there something like 'assume audio to be of X channel' in AVISynth to try (I know assumesamplerate only)?

Why don't you just ignore the audio in AviSynth (DirectshowSource("filename.ext", audio=false)) and mux the original AC3 audio separately?

Sure I could do, I just expected to convert that audio to a lower bitrate by VirtualDub (usually the easiest way for me).

Use NICAC3Source() if you want more consistency and audio separately (assuming you want to re-encode, not copy) , or FFMpegSource2("video.mkv",atrack=-1) if together in .mkv

Thanks, I have no NICAC3Source, will try find it later, but FFMpegSource2 wonderfully works perfect! But very very very slowly, it hangs a player for while before start (even after .ffindex is created), but audio is listed as 6ch.

I know you said you checked it, but you must have a downmix somewhere (I'm guessing either AC3Filter or FFDShow)

Really, Ive checked, no downmix there. Moreover, if I set downmix, it is played in 2.0 stereo and normal speed well.

If you want downmixed audio try disabling AC3Filter. See if ffdshow does any better.

Well. I actually I want downmix this time, but only this time, so I think that setting downmix in a place that could not be changed in AVS or in player/encoder settings is a bad idea...

[jagabo]

Have you tried a different AC3 source? Maybe there's just something wrong or unusual with the one your working with.

I didn't think AviSynth or VirtualDub could handle six channel audio but I just checked and both do (VirtualDub can't seem to play it and I don't think it can downmix it).

[lovyagin]

Sure I've tried other sources, since they all came from same people, I've created source myself. I take mkv with 6ch AAC (and YES, AVISynth open it properly), and converted it to MKV with 6ch AC3 (using virtualdub to make AVI and mkvtools to mux mkv). And it does not opened properly in AVISynth.

Finally I've disabled AC3filter at all (regsvr32 /u) instead of disabled it in settings (doesn't help) and it is work now perfectly! So, something is wrong with AC3filter in AVISynth.

But, unfortunately AC3filter, it is needed AC3filter for timeshift option of my TV Card... But I might use ffdshow although it is not recommended by device developer.

So solution for me is: do not use AC3filter. The question 'how to use ac3filter for 6ch audio in avisynth's directshowsource' still open, but, sorry, not so important for me currently. Thanks you a lot for helping.