LAV Filters - DirectShow Media Splitter and Decoders

[Mevunky]

I would look at avoiding multi-channel AAC content entirely? It is not a great way to do surround (hence why many receivers don't support it) this would go a long way to solving some of your problems.

[el Filou]

Why is AAC "not a great way to do surround"? It's certainly higher quality/size than AC3, and fine if you don't use the features associated with Dolby metadata.

[raymondjpg]

Originally Posted by Mevunky

I would look at avoiding multi-channel AAC content entirely? It is not a great way to do surround (hence why many receivers don't support it) this would go a long way to solving some of your problems.

It's not so much a matter of avoiding multi-channel AAC content as coping with it when it does arise. I acknowledge I do not see many examples of multi-channel AAC content, and it is some time since I last saw one.

I don't know why people use it to code media. It may be because source TV material is multi-channel AAC (probably unlikely because there are no AV receivers available to decode it) or because there is an attempt to maximise compression to keep file size to a minimum. In my neck of the woods we only have stereo TV channels and the tendency is to broadcast AC3 on HD channels, although there is some AAC on SD channels. In the past (some time ago) there was experimentation with multi-channel but IIRC it was AC3 audio.

While AC3 Filter and ffdshow still work in Windows 10 my HTPCs can transcode PCM decoded from all AAC formats by LAV filters, and given that bitstreaming with external LAV filters doesn't work for me in Windows 10, directing AC3Filter to be used for AC3 and DTS, and specifying those formats for bitstreaming in AC3 Filter, overcomes that obstacle.

I'd be more concerned that AC3 Filter and ffdshow might cease to work in future builds of Windows 10. I have no basis for that concern, but neither application has seen any development since 2012.

[arrgh]

@raymondjpg
I use a lot AAC5.1 in mkv, because it gives indeed a lot quality/size... for me it is the "HEVC for Audio"...
unfortunately I can not find an AV receiver which can decode it (at least I found nothing confirmed; on top of it, some say that this can not work, since HDMI is not specified to work with AAC);
since my old receiver requires DTS or DD (PCM maxed at 2 CH), I'm in a catch...

luckily MPC-BE's internal Audiorenderer is able to transcode AAC5.1 to AC3 on the fly; even on my small machine I have no (detectable) delay (very likely at the price of some additional quality loss)...
in any case, I hope MPC-BE will not drop this feature !

[raymondjpg]

Originally Posted by arrgh

luckily MPC-BE's internal Audiorenderer is able to transcode AAC5.1 to AC3 on the fly; even on my small machine I have no (detectable) delay (very likely at the price of some additional quality loss)...
in any case, I hope MPC-BE will not drop this feature !

I did not know that. I'll take another look at MPC-BE, but I've not been able so far to find a colour balance output from MPC-BE that I like the look of.

[Aleksoid1978]

Originally Posted by arrgh

luckily MPC-BE's internal Audiorenderer is able to transcode AAC5.1 to AC3 on the fly

Not Audio Renderer - Audio Decoder

[arrgh]

Originally Posted by Aleksoid1978

Not Audio Renderer - Audio Decoder

sorry, it's late...

@raymondjpg
at the moment my setup in MPC-BE is :
- external LAV-Splitter
- external LAV-Video-Decoder
- internal MPC-BE Audio-Decoder
- external subtitle renderer (I hope this time it's correct) XySubFilter
- external video renderer madVR

[raymondjpg]

Originally Posted by arrgh

@raymondjpg
at the moment my setup in MPC-BE is :
- external LAV-Splitter
- external LAV-Video-Decoder
- internal MPC-BE Audio-Decoder
- external subtitle renderer (I hope this time it's correct) XySubFilter
- external video renderer madVR

That combination is working well for me, except I am quite happy to use the internal sbtitle renderer.

Thanks for bringing it to my attention.

[el Filou]

@nevcairiel Would it be possible to add an option to the Mixing feature like 'only mix if less than 5 channels' ?

Explanation: I don't bitstream, and sometimes I encounter sources that need to be modified to output them in LPCM over my HDMI which only accepts 2.0, 5.1, and 7.1 (no idea if it's a limitation of the AVR, the HDMI standard, Windows, or NVIDIA ). Now, LAV has specific options to handle 1.0 > 2.0 and 6.1 > 7.1 and also an option to convert the rest to 5.1 by adding silent channels, but for cases like these:
- 4.0 L C R BC
- 4.0 L R SL SR
- 3.0 (or 3.1) L C R (LFE) (just encountered such a track on the Shin Godzilla Blu-ray which prompted me to ask)

-- so basically anything that is more than 2.0 but less than 5.0/5.1 -- I prefer to downmix them to 2.0 and then use PLII(x) in my receiver to upmix back rather than add silent channels because that doesn't sound as immersive.
An option 'only mix if less than 5 channels' would be great: LAV could then be configured to mix all those cases to 2.0 but not touch 5.1/6.1/7.1.

Thanks a lot if this sounds reasonable to you.

PS: maybe someone is going to answer that I could just enable mixing to 5.1/7.1 and check 'don't mix stereo sources', but I tried it and it doesn't apply PLII(x) decoding when doing that which I would like.

[ryrynz]

That sounds like a really great feature. Nice one.

[nevcairiel]

I'm not sure I agree its that great. There is so many corner cases where I don't see how some algorithm to create surround can be better then keeping the surround sound.

For example:

Originally Posted by el Filou

- 4.0 L C R BC

All this is missing is a LFE, otherwise it could nicely fill a 5.1 if you map the back-center to the surround channel.

Originally Posted by el Filou

- 4.0 L R SL SR

This already has dedicated surround channel, but no center. A center is IMHO not that crucial if your speakers are setup for a proper stereo image.

Honestly outside of special cases like 2.1 or 3.0 which barely have any channel beyond stereo, I'm not sure I see it.

[Sunspark]

In my case, I have a challenge with downmixing. My system is a 2.1 which I've had a long time. It's a good one, and I can only hear in 1 ear anyway so I haven't felt the need for anything with more channels.

Windows is set to stereo, and it comes out of the 3.5mm jack to the subwoofer, which then feeds the satellites. The sub has its own % dial, and the satellites are the volume control. I leave windows set at 67% volume because the output is not digital, though the player itself internally is set for 100%.

The problem is, even with MPC-HC set to exclusive mode and LAV downmixing to stereo, source material using 6 channel E-AC3, specifically L R C LFE Ls Rs which gets downmixed to 2.0, I am finding that a lot of dialogue, etc is too quiet or it feels like it has flat spots in the audio. I attempt to compensate for it by turning normalize on in the MPC-HC audio switcher options to 400% which helps make speech louder.

I just wonder if there's something I should try differently or if this is something LAV could do differently. I know MPC-HC in the audio switcher has an option which I've never tried, "enable custom channel mapping" for a # of input channels and you can place checks for a dizzying variety of positions but the MPC-HC programmer wrote years ago that this function should not be used for downmixing, and to do the downmixing in the decoder..

I find that source material which originates as stereo has louder and clearer speech than the 6-channel downmix to 2.0 equivalent in LAV.

Not expecting anything, just wondering if anything can potentially be downmixed differently whether via a different filter or some other method. Thanks!

[nevcairiel]

If you're using LAV to downmix to stereo, you can try increasing the center mix level, thats what usually contains the dialogue.
I would recommend 1.0 at first, and see how it sounds, and maybe a bit higher from there.

[Siso]

Originally Posted by nevcairiel

If you're using LAV to downmix to stereo, you can try increasing the center mix level, thats what usually contains the dialogue.
I would recommend 1.0 at first, and see how it sounds, and maybe a bit higher from there.

What about LFE when downmixing to stereo, it is set to 0, should we increase it?

[nevcairiel]

Its personal preference, and depending on the frequency response of your stereo speakers.

[Siso]

Originally Posted by nevcairiel

Its personal preference, and depending on the frequency response of your stereo speakers.

I see, thank you.

[el Filou]

Ah yes, I understand that it would only be useful for a limited number of quite rare sources. No worries, I can still enable mixing manually of course.
Just one question about your advice:

- 4.0 L C R BC
All this is missing is a LFE, otherwise it could nicely fill a 5.1 if you map the back-center to the surround channel.

Would it be such a good idea in practice to do that? I feel like it would create a weird surround effect (my system is actually 6.1 btw). Or am I missing some information here and a 4.0 layout like this was actually meant to be reproduced on 2 or 3 surround speakers and not just a single back center? IIRC this was the popular surround layout before digital discrete 5.1 (I only ever see such tracks on DVDs of 80s movies whose original audio wasn't remastered), and I have no idea how they were doing things.

I need to make some multichannel wav files manually and compare PLII downmix with silent channels when I have the time one day.

[clsid]

GCC 8.3 has been released.

[LigH]

Not yet available in MSYS2, I believe...

[clsid]

Nev makes his own mingw64 GCC builds. Several devs here use those.