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ac3 reencode channel mixed up

Started by bernd_b, October 19, 2012, 12:43:02 PM

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bernd_b

Are there any known problems concerning reencoding ac3?

I have a vob-File with ac3-5.1 Sound and after the reencode to h264/ac3 (Container mkv) the sound was mixed up. Using aften, no voices were audible, using lavc ac3 all voices where on the right channel.

Jan Gruuthuse

Why don't you keep the ac3 and use for audio: copy?
Please read this thread: AC3 5.1 to AAC 5.1 some explanation maybe found in Reply #7
If dts, that can/could/would cause issues?

bernd_b

I feared this question. I did this reencode to speed down a Pal Video  to the origninal Film-fps. So I need to reencode audio too, because the resulting video changes its length.

Here is the mediainfo of the source - i don't see that there is actually a dts stream:
mediainfo IN_TREATMENT_T5_S1_D2.Title1.vob
General
Complete name                            : IN_TREATMENT_T5_S1_D2.Title1.vob
Format                                   : MPEG-PS
File size                                : 1.32 GiB
Duration                                 : 25mn 32s
Overall bit rate mode                    : Variable
Overall bit rate                         : 7 379 Kbps

Video
ID                                       : 224 (0xE0)
Format                                   : MPEG Video
Format version                           : Version 2
Format profile                           : Main@Main
Format settings, BVOP                    : Yes
Format settings, Matrix                  : Custom
Duration                                 : 25mn 32s
Bit rate mode                            : Variable
Maximum bit rate                         : 9 800 Kbps
Width                                    : 720 pixels
Height                                   : 576 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 25.000 fps
Standard                                 : PAL
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Interlaced
Scan order                               : Top Field First
Compression mode                         : Lossy

Audio #1
ID                                       : 189 (0xBD)-128 (0x80)
Format                                   : AC-3
Format/Info                              : Audio Coding 3
Mode extension                           : CM (complete main)
Format settings, Endianness              : Big
Muxing mode                              : DVD-Video
Duration                                 : 25mn 32s
Bit rate mode                            : Constant
Bit rate                                 : 448 Kbps
Channel(s)                               : 6 channels
Channel positions                        : Front: L C R, Side: L R, LFE
Sampling rate                            : 48.0 KHz
Bit depth                                : 16 bits
Compression mode                         : Lossy
Stream size                              : 81.8 MiB (6%)

Jan Gruuthuse

Nothing we can do. As stated in AC3 5.1 to AAC 5.1:
Developers should have a look at the channel mapping in AC3 and  re-encoding in AC3 with Aften and lav.
- Channels are dropped/lost/put together/...
- Channels end up in wrong place
- Some documentation what the options should do in remix?

bernd_b

Did another try last week-end - nothing new so far I can see? :(

Isias


bernd_b

I uploaded a small TV record as an example.

What does not work:
Reencoding the ac3 6-Channel audio to 6-Channel (explicitly naming a remix or leaving this filter option unchecked). Resulting channels are mixed up (rear channels seem to become front channels)

What works:
- Reencoding the audio Track with remix to Dolby Pro Logic
- Reencoding the audio with other software from 5.1 to 5.1 audio, e.g. ffmpeg.

Latest test with avidemux 2.6 r8467 using aften as encoder.

Test File:
http://www.datafilehost.com/download-49733b73.html

mean