Scene with media source = 40-50% cpu usage

[Sturmlocke]

Hardware & Software:

• OpenSUSE 15.6 Leap
• AMD Ryzen 7 5700
• 32 GB DDR4 RAM
• 16TB NVME/HDD
• ASUS Prime B550M-K
• Thermaltake TR2 S 700W
• ASUS Dual Radeon RX 6600 V2 8GB GDDR6
• OBS installed as Flatpak
• OBS version: 30.2.3
• Stream settings (simple view): 24.000 kbps bitrate, x264 encoder, veryfast cpu preset
• Plugins: gstreamer Flatpak plugin installed

Scenes:

1. Black / empty scene
2. Intro (media source, 1 minute, 2k60 video, h264 format)
3. Gameplay at 2k60
4. Outro (media source, 30 seconds, 2k60 video, h264 format)

Infos:

When I start my Youtube stream, I use an intro file on my harddrive to start the stream, which is the first scene. The drives used for this are all NVME SSD. This is where my issue is. Doing this while live streaming to Youtube makes my cpu spike to higher numbers which seems to be resulting in a stuttery intro / outro video with audio issues sometimes. It doesn't happen every time, only sometimes. Here are some examples (cpu percentage as shown in OBS):

• Hardware acceleration when available checkbox enabled for media source, live streaming to Youtube: 30-40% CPU usage during the intro
• Hardware acceleration when available checkbox disabled for media source, live streaming to Youtube: 40-50% CPU usage during the intro
• Hardware acceleration when available checkbox enabled for media source, intro playback in OBS without streaming to Youtube: 3-4% CPU usage during the intro
• Hardware acceleration when available checkbox disabled for media source, intro playback in OBS without streaming to Youtube: 8-9% CPU usage during the intro
• Video playback in VLC without OBS: 1-3% CPU usage
• Lowering the bitrate from 24.000 to say 5000 during a live stream results in lower CPU usage during the intro playback (down to around 20%)

Gameplay live streaming after the intro results in around 10-20% CPU usage, 2k60 in both cases. Increasing the reso to 4k and 60 fps the CPU usage goes up to 30-35% CPU usage for gameplay. In both cases with x264 cpu, 24k bitrate etc. So gameplay can be streamed just fine whether it's 2/4k at 60fps. No dropped frames whatsoever. It's just the intro / outro file that can become stuttery sometimes.

Any ideas how to fix or improve this?

Cheers!