MPEG-4 videos play jerky in Kodi with kernel 5.10

[RigacciOrg]

After a plain install of 2021-01-11-raspios-buster-armhf-lite on a Raspberry Pi 4 Model B, I installed Kodi 18.7 and run it from a text console using the kodi-standalone script.
Playing some videos in MPEG-4 format encoded using the XviD library at 1366x768 and 6000 kbit/s I obtain a very jerky playback, almost unacceptable. The same videos play nicely if I install LibreELEC 9.2 or 10.0Beta on the same hardware. No problems with videos of similar quality, but encoded AVC using the x264 library.

The CPU load average goes above 1.3 and the palyback is so bad that I find several errors in kodi.log like this:

2021-04-01 13:00:04.286 T:2561659088 NOTICE: CVideoPlayerAudio::Process - stream stalled

The problem does not manifest in such gravity if I play the same videos using mplayer or ffplay into the graphical environment. I tried to run Kodi both under the pi and root user, but with no differencies.

Workaround

Using rpi-update I tried to upgrade and downgrade the kernel, the results are as follows:

• kernel 4.19.118-v7l+ Playback is OK, system seems stable.
• kernel 5.4.83-v7l+ Playback is OK, but system crashes on some videos (firmware crash)
• kernel 5.10.1-v7l+ Playback is jerky on MPEG-4
• kernel 5.10.17-v7l+ Playback is jerky on MPEG-4
• kernel 5.10.25-v7l+ Playback is jerky on MPEG-4

To be more precise I reverted to the following commits:

• 866751bfd023e72bd96a8225cf567e03c334ecc4 for Kernel 4.19, video OK, system stable
• 453e49bdd87325369b462b40e809d5f3187df21d for Kernel 5.4, video OK, system unstable

There are some bugs that may be related, but they not involve MPEG-4 videos: #4112, #4167 and #4223. I started a topic for my problem on raspberrypi.org/forums.

System

• Raspberry Pi 4 Model B
• Raspberry Pi reference 2021-01-11
• config.txt: gpu_mem=382, start_x=1, dtoverlay=vc4-fkms-v3d
• Linux raspberrypi 5.10.17-v7l+ # 1403 SMP Mon Feb 22 11:33:35 GMT 2021 armv7l GNU/Linux