Audio and video not synched on recordings

[Federico Fiore]

I use a cluster of 5 BBB servers. BigBlueButton Server 2.2.31 (2307)

I have notoiced that there are lessons recordings with audio and video not synched.

Settings in /usr/local/bigbluebutton/core/scripts/presentation.yml (generating mp4):

video_output_width: 640
video_output_height: 480
# Alternate output size to use when deskshare videos are present
# Set higher so that deskshare output is higher quality, but uses more space.
deskshare_output_width: 1280
deskshare_output_height: 720
# offset applied to audio in the output video file
# audio_offset = 1200 means that the audio will be delayed by 1200ms
audio_offset: 0
include_deskshare: true

# For PRODUCTION
publish_dir: /var/bigbluebutton/published/presentation
video_formats:
# - webm
- mp4

# For DEVELOPMENT
#publish_dir: /home/ubuntu/temp/published/presentation

My settings on /etc/bigbluebutton/bbb-conf/apply-config.sh (I don't using multikurento):

#!/bin/bash

# Pull in the helper functions for configuring BigBlueButton
source /etc/bigbluebutton/bbb-conf/apply-lib.sh

echo "  - Setting camera defaults"
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[6].bitrate 40
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[7].bitrate 80
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[8].bitrate 160
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[9].bitrate 320

yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[6].default true
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[7].default false
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[8].default false
yq w -i $HTML5_CONFIG public.kurento.cameraProfiles.[9].default false

echo "  - Setting browser title"
yq w -i $HTML5_CONFIG public.app.clientTitle "BigBlueButton"

And in the file "/usr/local/bigbluebutton/core/lib/recordandplayback/generators/video.rb" for processing mp4 I have setted:

{
        extension: 'mp4',
        parameters: [
          # These settings are appropriate for medium quality at any resolution
          # Increase -threads (or remove it, to use all cpu cores) to speed up processing
          # You can also change the preset: try 'fast' or 'faster'
          # To change quality, adjust the -crf value. Lower numbers are higher quality.
          #%w[-c:v libx264 -crf 23 -threads 2 -preset medium -g 240
          %w[-c:v libx264 -crf 23 -threads 32 -preset medium -g 240
             -c:a aac -b:a 64K
             -f mp4 -movflags faststart]
        ],
        postprocess: [ ]
      }

Why I have in some recordings audio and video not synched?

My settings are correct?

Thanks to anyone that can help me