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Topic: MKVs: downmix ac3 6-channels to ac3 2-channels and remux (Read 5583 times) previous topic - next topic

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  • kwanbis
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  • Developer (Donating)
MKVs: downmix ac3 6-channels to ac3 2-channels and remux
I have a WD TV, and somehow, MKVs with 6 channels ac3 do not play sound on my TV, but 2 channels ones ac3 do.

UPDATE: I had my WD TV to DIGITAL AUDIO, instead than STEREO.

It looks like if the audio is 2 channels, the WD TV would do STEREO anyway, but for the 6 channels, it would try to do DIGITAL.

So i set it back to STEREO and all is playing perfectly.

But i'm still interested on knowing:

1) how can i specify FPS while doing the MKVmerge on the command line:
mkvmerge -o test.mkv video.h264 audio.ac3 sub.srt

EDIT2: --default-duration 0:24000/1001fps would do it.

2) if i already have an mkv, how do i add another file to it?
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------------------------- OLD POST --------------------------------

So i'm trying to find out the quickets way of extracting the the ac3, downsampling it to 2 channels, and then remerging to the mkv.

I-m experimenting a little, since i-m really not much into video, unless i need to do something like now, so:

1) eac3to a.mkv
MKV, 1 video track, 1 audio track, 0:41:46, 24p /1.001
1: h264/AVC, English, 720p24 /1.001
2: AC3, 5.1 channels, 384kbps, 48khz, dialnorm: -27dB

2) eac3to a.mkv 1: video.h264 2: audio.ac3

3) eac3to audio.ac3 audio2.ac3 -down2

4) eac3to audio.ac3 audio2.wav

5) neroaacenc.exe -q 1 -if audio2.wav -of audio2.aac

So now i have:

video.h264 (original video)
audio.ac3 (this is the original 6 channels ac3)
audio2.ac3 (ac3 downsampled to 2 channels)
audio2.aac (aac downsampled to 2 channels)

I then tried:

mp4box -add "video.h264:fps=23.976" -add "audio2.aac:lang=en" "a-audio2-aac.mp4"

mp4box -add "video.h264:fps=23.976" -add "audio2.ac3:lang=en" "a-audio2-ac3.mp4"

mkvmerge -o a-audio2-aac.mkv video.h264 audio2.aac

mkvmerge -o a-audio2-ac3.mkv video.h264 audio2.ac3

I ended up with:

a-audio2-aac.mp4 plays perfectly.

a-audio2-ac3.mp4 no sound (is an mp4 restriction?)

a-audio2-ac3.mkv 1 sec delay

a-audio2-aac.mkv 1 sec delay

So, i was wondering, why the 1 sec delay (audio plays latter than the vide)? Is it because i-m not specifying the FPS? How do i do it?

And last, since i already have an MKV with audio and ac3, how can i add the 2 channel ac3?

Thanks.
  • Last Edit: 10 March, 2009, 06:09:11 PM by kwanbis

  • smok3
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MKVs: downmix ac3 6-channels to ac3 2-channels and remux
Reply #1
oh well, you just have to test and find whatever will work, i would go for a final file that looks like:

1. video
2. new stereo audio, can you use AAC here?
3. original ac3
.mkv

(so basically i would go for insertion of the new stereo track into original file, that way you can still play ac3 with some PC)

edit: if you can post a small sample somewhere i may find time to play around.
  • Last Edit: 10 March, 2009, 05:53:10 AM by smok3
PANIC: CPU 1: Cache Error (unrecoverable - dcache data) Eframe = 0x90000000208cf3b8
NOTICE - cpu 0 didn't dump TLB, may be hung

  • kwanbis
  • [*][*][*][*][*]
  • Developer (Donating)
MKVs: downmix ac3 6-channels to ac3 2-channels and remux
Reply #2
UPDATE: I had my WD TV to DIGITAL AUDIO, instead than STEREO.

It looks like if the audio is 2 channels, the WD TV would do STEREO anyway, but for the 6 channels, it would try to do DIGITAL.

So i set it back to STEREO and all is playing perfectly.

But i'm still interested on knowing:

1) how can i specify FPS while doing the MKVmerge on the command line:
mkvmerge -o test.mkv video.h264 audio.ac3 sub.srt

2) if i already have an mkv, how do i add another file to it?
  • Last Edit: 10 March, 2009, 05:14:44 PM by kwanbis

  • smok3
  • [*][*][*][*][*]
  • Moderator
MKVs: downmix ac3 6-channels to ac3 2-channels and remux
Reply #3
1. http://www.bunkus.org/videotools/mkvtoolni...c/mkvmerge.html
try −−default−duration 25fps
2. no idea, but −−append−to seems to be it.
  • Last Edit: 11 March, 2009, 07:05:37 AM by smok3
PANIC: CPU 1: Cache Error (unrecoverable - dcache data) Eframe = 0x90000000208cf3b8
NOTICE - cpu 0 didn't dump TLB, may be hung

  • CoyoteSmith
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MKVs: downmix ac3 6-channels to ac3 2-channels and remux
Reply #4
2) if i already have an mkv, how do i add another file to it?[/b]

open both files (your .mkv and other file) in mkvtoolnix, select which audio,video and subtitle tracks you want to remain in the container than mux it again