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  1. Hi, I want to merge two audio track with delay for one of this (in ms) in ffmpeg
    Problem, I have one in .AC3 and an other in .AAC

    Why i want to do this ?
    I have two source of a video with the same duration but i don't know why, with my earphone with the .AC3 only the the right earpiece work and with the .ACC only the left work.

    Thanks for your help and sorry if i don't anwser the next hour I will not be present.
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  2. Post an mediainfo report (text mode) of both videos here
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  3. Code:
    General
    Format                                   : ADTS
    Format/Info                              : Audio Data Transport Stream
    File size                                : 88.1 MiB
    Overall bit rate mode                    : Variable
    
    Audio
    Format                                   : AAC LC
    Format/Info                              : Advanced Audio Codec Low Complexity
    Format version                           : Version 4
    Codec ID                                 : 2
    Bit rate mode                            : Variable
    Channel(s)                               : 2 channels
    Channel layout                           : L R
    Sampling rate                            : 48.0 kHz
    Frame rate                               : 46.875 FPS (1024 SPF)
    Compression mode                         : Lossy
    Stream size                              : 88.1 MiB (100%)
    Code:
    General
    Format                                   : AC-3
    Format/Info                              : Audio Coding 3
    Commercial name                          : Dolby Digital
    File size                                : 86.4 MiB
    Duration                                 : 1 h 34 min
    Overall bit rate mode                    : Constant
    Overall bit rate                         : 128 kb/s
    
    Audio
    Format                                   : AC-3
    Format/Info                              : Audio Coding 3
    Commercial name                          : Dolby Digital
    Duration                                 : 1 h 34 min
    Bit rate mode                            : Constant
    Bit rate                                 : 128 kb/s
    Channel(s)                               : 2 channels
    Channel layout                           : L R
    Sampling rate                            : 48.0 kHz
    Frame rate                               : 31.250 FPS (1536 SPF)
    Compression mode                         : Lossy
    Stream size                              : 86.4 MiB (100%)
    Service kind                             : Complete Main
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  4. I meant the full information, incl. Videostream and others.
    BTW, both audio tracks are stereo (2 channels) so it is very unlikely that both tracks have only 1 channel of audio each.
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  5. Code:
    General
    Format                                   : Matroska
    Format version                           : Version 1
    File size                                : 1.41 GiB
    Duration                                 : 1 h 34 min
    Overall bit rate                         : 2 133 kb/s
    Encoded date                             : UTC 2019-12-04 11:52:05
    Writing library                          : WonderShare Matroska Muxer
    
    Video
    ID                                       : 1
    Format                                   : AVC
    Format/Info                              : Advanced Video Codec
    Format profile                           : Main@L4.1
    Format settings                          : CABAC / 2 Ref Frames
    Format settings, CABAC                   : Yes
    Format settings, Reference frames        : 2 frames
    Format settings, GOP                     : M=3, N=25
    Codec ID                                 : V_MPEG4/ISO/AVC
    Duration                                 : 1 h 34 min
    Bit rate                                 : 1 963 kb/s
    Width                                    : 640 pixels
    Height                                   : 480 pixels
    Display aspect ratio                     : 4:3
    Frame rate mode                          : Constant
    Frame rate                               : 29.970 (30000/1001) FPS
    Color space                              : YUV
    Chroma subsampling                       : 4:2:0
    Bit depth                                : 8 bits
    Scan type                                : Progressive
    Bits/(Pixel*Frame)                       : 0.213
    Stream size                              : 1.29 GiB (92%)
    Default                                  : Yes
    Forced                                   : No
    
    Audio
    ID                                       : 2
    Format                                   : AC-3
    Format/Info                              : Audio Coding 3
    Commercial name                          : Dolby Digital
    Codec ID                                 : A_AC3
    Duration                                 : 1 h 34 min
    Bit rate mode                            : Constant
    Bit rate                                 : 128 kb/s
    Channel(s)                               : 2 channels
    Channel layout                           : L R
    Sampling rate                            : 48.0 kHz
    Frame rate                               : 31.250 FPS (1536 SPF)
    Bit depth                                : 16 bits
    Compression mode                         : Lossy
    Stream size                              : 86.4 MiB (6%)
    Service kind                             : Complete Main
    Default                                  : Yes
    Forced                                   : No

    Code:
    General
    Format                                   : Matroska
    Format version                           : Version 4
    File size                                : 1 016 MiB
    Duration                                 : 1 h 34 min
    Overall bit rate mode                    : Variable
    Overall bit rate                         : 1 506 kb/s
    Encoded date                             : UTC 2021-10-27 15:53:37
    Writing application                      : mkvmerge v61.0.0 ('So') 64-bit
    Writing library                          : libebml v1.4.2 + libmatroska v1.6.4
    Cover                                    : Yes
    Attachments                              : cover.bmp
    
    Video
    ID                                       : 1
    Format                                   : AVC
    Format/Info                              : Advanced Video Codec
    Format profile                           : Main@L3
    Format settings                          : CABAC / 1 Ref Frames
    Format settings, CABAC                   : Yes
    Format settings, Reference frames        : 1 frame
    Format settings, GOP                     : M=1, N=15
    Codec ID                                 : V_MPEG4/ISO/AVC
    Duration                                 : 1 h 34 min
    Bit rate mode                            : Variable
    Bit rate                                 : 1 373 kb/s
    Maximum bit rate                         : 2 058 kb/s
    Width                                    : 640 pixels
    Height                                   : 480 pixels
    Display aspect ratio                     : 4:3
    Frame rate mode                          : Constant
    Frame rate                               : 29.970 (30000/1001) FPS
    Color space                              : YUV
    Chroma subsampling                       : 4:2:0
    Bit depth                                : 8 bits
    Scan type                                : Progressive
    Bits/(Pixel*Frame)                       : 0.149
    Stream size                              : 927 MiB (91%)
    Default                                  : Yes
    Forced                                   : No
    Color primaries                          : BT.601 NTSC
    Transfer characteristics                 : BT.709
    Matrix coefficients                      : BT.601
    
    Audio
    ID                                       : 2
    Format                                   : AAC LC
    Format/Info                              : Advanced Audio Codec Low Complexity
    Codec ID                                 : A_AAC-2
    Duration                                 : 1 h 34 min
    Bit rate                                 : 128 kb/s
    Channel(s)                               : 2 channels
    Channel layout                           : L R
    Sampling rate                            : 48.0 kHz
    Frame rate                               : 46.875 FPS (1024 SPF)
    Compression mode                         : Lossy
    Stream size                              : 86.4 MiB (8%)
    Language                                 : French
    Default                                  : Yes
    Forced                                   : No
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  6. Cut from video 1 (with ac3 audio) 20 seconds from position 10 minutes with avidemux and post it here
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  7. If really each audio track has one silent channel (weird but I've seen / heard weird things like that on supposedly professionally made DVDs), there's no point in merging the “good” channel from each one, just convert one track (the best sounding one obviously, if any — it is likely that the AAC track was transcoded from the native AC3 track, which would be stupid since they have the same rather low bitrate, if that's indeed the case stick with the AC3 — what's puzzling is why on Earth the channels were reversed ?) to mono by discarding the silent channel, or duplicate the “good” channel to get double mono (may be better for compatibility reasons — some standalone devices may prefer not to read mono audio, although I have no evidence of that). This can be done quite easily with Audacity, perhaps a single ffmpeg command would do the trick but I wouldn't know how to proceed.
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