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Old 10th November 2011, 21:40   #1  |  Link
madhatter300871
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Behappy and aften question

Hi

Am I understanding correctly from what I have read about Aften and Behappy :-

1. Behappy can take a 5.1 source and, via avisynth, downmix to stereo, DPLI, DPLII and DPLII with FLE ?

2. DPLII with LFE is simply that it includes the LFE channel ?

3. If I downmix, I then MUST specify Dolby Surround mode as "Dolby Surround mode encoded" in aften (-dsur switch) ?

4. Aften dynamic range switch (-dynrng) inserts meta data to tell the decoder to apply DRC, it doesnt apply this DRC during encoding ?

5. Dialogue normalisation switch (-dnorm) inserts meta data to tell the decoder to apply normalisation, it doesnt apply this during encoding ?

6. Aften alternative bit stream syntax switches (-xbis1 and -xbis2) inserts meta data to tell the decoder the downmix mode (lo/ro or lt/rt) and mix levels. Do I need to know how the downmix was performed if I am going to set these switches ?

7. The centre mix and surround mix switches (-cmix, -smix) inserts meta data to tell the decoder the mix levels to apply if it downmixes to stereo ?

Also a quick question on Dolby headphone (just for my own knowledge, I dont plan to do any encodes of this format). Does a Dolby Headphone encoded stream have 5.1 channels or is it another type of stereo downmixing like DPL and dolby headphone is just a method of decoding them for headphone listening ?

I read up on avconv, from the libav website, and think I have filled in the gaps from what I didn't really understand about aften. Would appreciate if some of you guys can confim my understanding.

Thanks.

Last edited by madhatter300871; 10th November 2011 at 21:55.
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Old 11th November 2011, 00:11   #2  |  Link
tebasuna51
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1) Yes
2) Yes
3) Yes, if your downmix is DPLI or DPLII
4) Yes
5) Yes
6,7) Let defaults or read more here: http://www.atsc.org/cms/standards/a_52-2010.pdf

Dolby headphone is it another type of stereo downmixing for headphone listening.
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Old 11th November 2011, 09:35   #3  |  Link
madhatter300871
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Tebasuna51 -- Thanks.

That pdf is an in depth read ! Well I think I have found what i wanted, but would appreciate if you could confirm I have understood correctly.

The centre mix and surround mix switches (-cmix, -smix) only indicate to the decoder the nominal downmix level of the centre and surround channels when downmixing to stereo ?
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Old 11th November 2011, 11:34   #4  |  Link
tebasuna51
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Yes.

BTW, I always use defaults for these parameters about ac3 metadata.
Only use:

- dsur 2 (for stereo Dolby Surround mode)

-xbsi2 1 -dsurexmod 2 (for flag the 5.1 AC3 to EX)

AC3-EX is when a Back Center channel was mixed to surround channels.
For instance, if your source is a DTS 6.1 discrete decoded by eac3to-ArcSoft to a 6.1 WAV and use like input to BeHappy this .avs file:
Code:
a = RaWavSource("d:\path\6.1.wav").ConvertAudioToFloat()
fl = GetChannel(a, 1)
fr = GetChannel(a, 2)
fc = GetChannel(a, 3)
lf = GetChannel(a, 4)
bc = GetChannel(a, 5)
sl = GetChannel(a, 6)
sr = GetChannel(a, 7)
bl = MixAudio(sl, bc, 1.0, 0.7071) # mix bc with sl at -3 dB
br = MixAudio(sr, bc, 1.0, 0.7071) # mix bc with sr at -3 dB
MergeChannels(fl, fr, fc, lf, bl, br)
Normalize()
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Old 11th November 2011, 16:05   #5  |  Link
madhatter300871
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tebasuna51 -- Thanks a lot. It's always nice to have confirmation that I have understood right.

Think I know what I am doing now, I have no more question.
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Old 19th November 2011, 13:56   #6  |  Link
madhatter300871
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I do have more questions ... sorry !

1. Is stereo rematrixing only to be used when encoding a stereo AC3 track, or can it also be used when encoding a multichannel AC3 track ?
2. Whats the difference between -cmix/-smix and the extended info for downmix mode, lo/ro lt/rt and mix levels ? When would you use one method over another ?
Thanks.

Last edited by madhatter300871; 19th November 2011 at 15:19.
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Old 19th November 2011, 19:14   #7  |  Link
tebasuna51
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1. Only stereo
2. More info about Dolby Metadata
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Old 22nd November 2011, 16:09   #8  |  Link
madhatter300871
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tebasuna51...thanks again.

I read the pdf at the link you gave, and if I understand correctly then aften uses the -smix and -cmix settings as the default for telling the decoder the stereo downmix levels when xbis1 extended data has not been specified. These are overridden by the xbis setting, if they are set. These can subsequently be over riden again by the user if such an option exists on the playback device.

OK, I'll probably not bother setting the xbis settings to be honest and just go with the defaults, as specified by -cmix and -smix in aften. My early tests using aften do give great results using these defaults.

I don't 'think' I have any more questions .... famous last words !
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