ac3 reencode channel mixed up

[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:

Code Select Expand

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]

I can confirm this problem.

[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]

thanks for the sample