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  1. Member
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    Apr 2019
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    Hello,

    I have been trying to exchange an English language audio for a Russian language audion, in a video file. The file is in MP4 format with a coanstant rate video and variable rate audio. I take a constant rate audio from a different file and try to insert the audio track into the video file, effectively exchanging the Russian audio track for an English audio track. The audio begins synced but quickly de-syncs. The duration of video and audio are identical. I use ffmpeg or Avidemux.
    Currently, I'm using Handbrake to make a copy of the film with a constant rate audio track which I can then use. This will take about eight hours.
    Is there a quicker way, using ffmpeg?
    Is the variable nature of the audio track embedded in the video file, thus requiring conversion of any audio track candidate into a variable audio track?
    To re-phrase, if a video (constant bit rate) has an audio with variable frame rate, must any substitute, also have a variable bit rate?

    Thank you
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  2. Member Cornucopia's Avatar
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    Audio "rates" that are referring to are data birates: cbr, vbr, abr. Audio does not have a framerate in the sense that video does, so it will NOT have a variable samplerate. EVER. If it did, you would know immediately, because it would have horrible pitch problems (wow, flutter, warbling, etc).

    Audio data rates DO NOT affect its runtime, sync, or anything else time-related so if you are having issues with syncing, it is probably due to some other issue: different video lengths, edits, non-matching timebases (using 30 when you should be using 29.97).

    Give us more info.

    Scott
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  3. Member
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    Hello,

    Thanks for responding.
    I'm using MediaInfo for metadata retrieval. The original video data:
    ===================== Video =====================
    Id : 1
    Format : AVC
    Format info : Advanced Video Codec
    Formatprofile : High@L5.1
    Formatsettings, CABAC : Yes
    Formatsettings, ReFrames : 4 frames
    Codec Id : avc1
    Codec info : Advanced Video Coding
    Duration (ms) : 2h 33mn
    Bit rate : 22.9 Mbps
    Width : 3 840 pixels
    Height : 2 160 pixels
    Display aspect ratio : 16:9
    Frame rate mode : Constant
    Frame rate : 24.000 fps
    Color space : YUV
    Chroma subsampling : 4:2:0
    Bit depth : 8 bits
    Scan type : Progressive
    Bits/(Pixel*Frame) : 0.115
    Stream size : 24.5 GB (99%)
    Tagged date : UTC 2017-10-13 14:47:40
    Menus : 0

    ===================== Audio =====================
    Id : 2
    Format : AAC
    Format info : Advanced Audio Codec
    Formatprofile : LC
    Codec Id : 40
    Duration (ms) : 2h 33mn
    Duration_FirstFrame : 18ms
    Duration_LastFrame : -10ms
    Bit rate mode : Variable
    Bit rate : 243 Kbps
    Maximum bit rate : 249 Kbps
    Channel(s) : 2 channels
    Channel positions : Front: L R
    Sampling rate : 44.1 KHz
    Frame rate : 43.066 fps (1024 spf)
    Compression mode : Lossy
    Stream size : 266 MB (1%)
    Default : Yes
    Alternate group : 1
    Tagged date : UTC 2017-10-13 14:47:40
    Menus : 0

    ======================================
    ======================================

    The data for the file from which the audio is extracted is:

    ===================== Video =====================
    Id : 1
    Format : AVC
    Format info : Advanced Video Codec
    Formatprofile : High@L3.1
    Formatsettings, CABAC : Yes
    Formatsettings, ReFrames : 4 frames
    Formatsettings, GOP : M=1, N=72
    Codec Id : avc1
    Codec info : Advanced Video Coding
    Duration (ms) : 2h 33mn
    Duration_FirstFrame : 46ms
    Bit rate : 2 164 Kbps
    Width : 1 280 pixels
    Height : 532 pixels
    Display aspect ratio : 2.40:1
    Original display aspect rat : 2.40:1
    Frame rate mode : Constant
    Frame rate : 24.000 fps
    Color space : YUV
    Chroma subsampling : 4:2:0
    Bit depth : 8 bits
    Scan type : Progressive
    Bits/(Pixel*Frame) : 0.132
    Stream size : 2.30 GB (91%)
    Writing library : x264 core 152 r2851 ba24899
    Encoding settings : cabac=1 / ref=4 / deblock=1:2:2 / analyse=0x3:0x113 / me=hex / subme=2 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=17 / lookahead_threads=4 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=0 / weightp=2 / keyint=72 / keyint_min=7 / scenecut=0 / intra_refresh=0 / rc_lookahead=40 / rc=abr / mbtree=1 / bitrate=2164 / ratetol=1.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=0.91 / aq=1:1.00
    Tagged date : UTC 2018-07-07 17:27:51

    ===================== Audio =====================
    Id : 2
    Format : AAC
    Format info : Advanced Audio Codec
    Formatprofile : LC
    Codec Id : 40
    Duration (ms) : 2h 33mn
    Duration_LastFrame : -4ms
    Bit rate mode : Constant
    Bit rate : 204 Kbps
    Channel(s) : 2 channels
    Channel positions : Front: L R
    Sampling rate : 44.1 KHz
    Frame rate : 43.066 fps (1024 spf)
    Compression mode : Lossy
    Stream size : 224 MB (9%)
    Default : Yes
    Alternate group : 1
    Tagged date : UTC 2018-07-07 17:27:51
    ======================================
    ======================================

    The audio section, in each file, refers to a "Bit rate mode", this is what I am quoting.
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  4. Member Cornucopia's Avatar
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    Right. Hence my 2nd paragraph.

    If you want to compare them put both audio streams in a DAW. Then you'll know whether they should sync or not. If they do, then there is something faulty with your re-encoding and/or re-muxing process. If they don't sync, you have editing or time compression/expansion to do first to get them into sync.

    Scott
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  5. Member
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    Hello,

    Thanks.
    I loaded both sound tracks into Audacity and both were synchronized.
    I use ffmpeg and Avidemux, which also uses ffmpeg, I believe. I had to download a converter to convert the aac format to wav for use with Audacity.
    Every time I've encountered a video with a variable bit rate audio, I've encountered this sync problem.

    Any suggestions for software to replace ffmpeg?

    Thank you
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