Check advice from here: https://wiki.libreelec.tv/configuration/4k-hdr#hdr
Using 1080p60 for GUI with 4k modes enabled is whitelist is recommended configuration. (You will get 4k resolution for video).
Running the GUI iat 4k is pointless (the skin texures are 1080p) and just makes kodi laggier.
That's it! I change my resolution to 1920x1080 and enable hw acceleration again and all works fine now: audio and video are syncron again, also for video in high definition.
Perfect 
I switch to OSMC and this problem exists also there. BUT: If I disable hardware acceleration in the settings there, video and audio is syncron! Only the video stutters sometime a little bit.
The problem is not the delay of microseconds with the lip-sync, the problem is the delay of many seconds between audio and video !
The same file from the same source with just another lower resolution works fine:
https://rodlzdf-a.akamaihd.net/dach/zdf/21/12…360k_p35v15.mp4
Generally this problem exists with nearly all files from this source: High resolution variante of the file has excessive delay, lower resolution variante works fine.
Problem only exists with Pi4 and LE 10, on a Pi4 with LE9 or a Pi3 with LE9 or a PC with Kodi all files play well including the high variante.
This is a pity 
I will revert my libreelec version back to 9.2 now.
For me, the link works:
wget https://rodlzdf-a.akamaihd.net/dach/zdf/21/12/211221_2015_sendung_iat/5/211221_2015_sendung_iat_a1a2_3360k_p36v15.mp4
--2022-02-07 13:07:52-- https://rodlzdf-a.akamaihd.net/dach/zdf/21/12/211221_2015_sendung_iat/5/211221_2015_sendung_iat_a1a2_3360k_p36v15.mp4
Resolving rodlzdf-a.akamaihd.net (rodlzdf-a.akamaihd.net)... 2.16.186.66, 2.16.186.65
Connecting to rodlzdf-a.akamaihd.net (rodlzdf-a.akamaihd.net)|2.16.186.66|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 974707755 (930M) [video/mp4]
Saving to: ‘211221_2015_sendung_iat_a1a2_3360k_p36v15.mp4’
211221_2015_sendung_iat_a1a2_3360k_p36v15.mp4 7%[==========> ] 70,01M 56,3MB/s
I put a link in my message:
Don't know why it is not showing 
So I give it another try:
BTW: The same file plays fine with an Raspi 3 and Libreelec 9.2.8 ...
A sample file would be https://rodlzdf-a.akamaihd.net/dach/zdf/21/12/211221_2015_sendung_iat/5/211221_2015_sendung_iat_a1a2_3360k_p36v15.mp4
It is an episode of a german tv series "In 80 Tagen um die Welt" and can be downloaded for free from the mediathek of ZDF.
The delay immediately starts at the beginning of the file.
I find out that the problem only exists with some video files. One of the "bad" files has this parameter:
mediainfo S01E08.mp4
General
Complete name : S01E08.mp4
Format : MPEG-4
Format profile : Base Media / Version 2
Codec ID : mp42 (isom/mp42)
File size : 945 MiB
Duration : 47 min 29 s
Overall bit rate mode : Variable
Overall bit rate : 2 782 kb/s
Encoded date : UTC 2021-12-10 17:26:14
Tagged date : UTC 2021-12-10 17:26:14
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 5 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 5 frames
Format settings, GOP : M=2, N=100
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 47 min 29 s
Bit rate mode : Variable
Bit rate : 2 612 kb/s
Maximum bit rate : 3 199 kb/s
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 50.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.057
Stream size : 887 MiB (94%)
Language : German
Encoded date : UTC 2021-12-10 17:26:14
Tagged date : UTC 2021-12-10 17:26:17
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Codec configuration box : avcC
Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 47 min 29 s
Bit rate mode : Constant
Bit rate : 160 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 : 54.3 MiB (6%)
Language : German
Encoded date : UTC 2021-12-10 17:26:14
Tagged date : UTC 2021-12-10 17:26:17When I convert it into another format (eg. with handbrake) the file could be played without problems. The converted file has this parameter:
mediainfo S01E08.m4v
General
Complete name : S01E08.m4v
Format : MPEG-4
Format profile : Base Media / Version 2
Codec ID : mp42 (mp42/iso2/avc1/mp41)
File size : 789 MiB
Duration : 47 min 29 s
Overall bit rate : 2 324 kb/s
Movie name : S01E08
Encoded date : UTC 2022-02-01 17:45:12
Tagged date : UTC 2022-02-01 17:45:12
Writing application : HandBrake 1.5.1 2022011100
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 5 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 5 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 47 min 29 s
Bit rate : 1 515 kb/s
Width : 1 280 pixels
Height : 640 pixels
Display aspect ratio : 2.000
Frame rate mode : Variable
Frame rate : 29.754 FPS
Minimum frame rate : 25.000 FPS
Maximum frame rate : 30.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.062
Stream size : 515 MiB (65%)
Writing library : x264 core 161
Encoding settings : cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=8 / psy=1 / psy_rd=1,00:0,00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=18 / lookahead_threads=3 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=300 / keyint_min=30 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=crf / mbtree=1 / crf=20,0 / qcomp=0,60 / qpmin=0 / qpmax=69 / qpstep=4 / vbv_maxrate=25000 / vbv_bufsize=31250 / crf_max=0,0 / nal_hrd=none / filler=0 / ip_ratio=1,40 / aq=1:1,00
Encoded date : UTC 2022-02-01 17:45:12
Tagged date : UTC 2022-02-01 17:45:12
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Codec configuration box : avcC
Audio #1
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 47 min 29 s
Source duration : 47 min 29 s
Bit rate mode : Constant
Bit rate : 160 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 : 54.3 MiB (7%)
Source stream size : 54.3 MiB (7%)
Title : Stereo / Stereo
Language : German
Default : Yes
Alternate group : 1
Encoded date : UTC 2022-02-01 17:45:12
Tagged date : UTC 2022-02-01 17:45:12
Fallback From : 3
mdhd_Duration : 2849237
Audio #2
ID : 3
Format : AC-3
Format/Info : Audio Coding 3
Commercial name : Dolby Digital
Codec ID : ac-3
Duration : 47 min 29 s
Source duration : 47 min 29 s
Bit rate mode : Constant
Bit rate : 640 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 : 217 MiB (28%)
Source stream size : 217 MiB (28%)
Title : Stereo / Stereo
Language : German
Service kind : Complete Main
Default : Inherited From: 2
Alternate group : 1
Encoded date : UTC 2022-02-01 17:45:12
Tagged date : UTC 2022-02-01 17:45:12
Fallback To : 2
mdhd_Duration : 2849211I could not find out which of the parameter makes the different .....
As mentioned in the linked URL above I have exactly the same problem with the same hardware: Pi4 with 2GB RAM, running from external ssd connected via USB 3.0. The TV is a Samsung 4K and the problem raises in any combinations:
- various video formats
- loading files from nfs or local ssd
- with or without audio passthrough
- via AVR or directly via HDMI on TV
If you need more information or debug logs, please tell me and I will try to send it.
One more question: In an older forum entry relating to LE7 I found the hint to disable "sync playback to display". May it help for LE10 also? Where can I find this option in the menu?
I'm still having this audio delay problem on my pi4, none of the above solutions/hints fix the problem.
With libreelec 9.2 my pi4 worked very well, the audio problem starts with libreelec 10, so I think it is not a hardware problem.
Are there any other things I can try to fix it?