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My procedure is as follows:

  1. convert the videos to 1920x1080 at 60 FPS (some videos had only 30 FPS)
  2. save the converted videos in a text file
  3. merging the video by an FFMPEG concat

After the videos are merged, the audio is out of sync with the video.

To convert the videos I use the following command: ffmpeg -i input.mp4 -vf scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:-1:-1,setsar=1 -r 60 output.mp4 (got it from here: How can I upscale videos with FFmpeg to a fixed resolution?)

My FFMPEG command to concat the videos: ffmpeg -f concat -safe 0 -i videolist.txt -c copy final.mp4

When I concatonate the videos, I sometimes get a lot of these warnings:

[mp4 @ 0x55740b62ad40] Non-monotonous DTS in output stream 0:1; previous: 336921, current: 336064; changing to 336922. This may result in incorrect timestamps in the output file.

A question for the FFMPEG professionals, how can I make sure that video and audio are in sync?

UPDATE: Here are the details of the files being listed in the videolist.txt

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'intro.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:00:07.04, start: 0.000000, bitrate: 291 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 187 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 91 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '4t6Brqa4E5BnD6vC5inICusEtPtd3nU88NgbmUJ.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:00:37.66, start: 0.000000, bitrate: 1608 kb/s
    Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 1532 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #2, mov,mp4,m4a,3gp,3g2,mj2, from 'cut.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:00:00.65, start: 0.000000, bitrate: 7128 kb/s
    Stream #2:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 7576 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #2:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 115 kb/s (default)
    Metadata:
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
Input #3, mov,mp4,m4a,3gp,3g2,mj2, from '80SEh7RoTyVPNj3zTZSaixxATvUYXMNyzu15evs.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:00:07.75, start: 0.000000, bitrate: 1191 kb/s
    Stream #3:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 1106 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #3:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 70 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #4, mov,mp4,m4a,3gp,3g2,mj2, from 'outro.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:00:15.17, start: 0.000000, bitrate: 3417 kb/s
    Stream #4:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 3286 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #4:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Tobias
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1 Answers1

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All attributes must be the same, but your audio has varying channel layouts (stereo & mono) and sample rates (48000 & 44100).

Add -ar 48000 -ac 2 to your command:

ffmpeg -i input.mp4 -vf scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:-1:-1,setsar=1 -r 60 -ar 48000 -ac 2 output.mp4

Alternatively, if you want to avoid any temporary files you can do everything in one command using the concat filter as shown in How to concatenate videos in ffmpeg with different attributes?.

llogan
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