quick update:
i can now safely say that my problem of losing HDMI signal in 25fps videos is connected with showing the progress bar during playback with hyperion active.
Using the settings suggested by hias, playback per se works. but as stated above, as soon as i press any button that pops up the progress bar , HDMi signal will be lost after a second or so. i can reproduce this with any kind of 25fps video. Due to copyright reasons i am reluctant to upload anything, but i checked it with some youtube video with the same results (HIS DARK MATERIALS Trailer (2019) - YouTube -> downloaded as mp4).
i was also mistaken that the machine doesn't come back up if i force it to reboot... it just takes about 5 minutes (no kidding) to be back up in this case. this is on a RPI4 4gb connected to a LG Oled C9 with 106 APA102 LEDs.
any ideas would be much appreciated
General
Complete name : HIS DARK MATERIALS Trailer (2019) (1080p_25fps_H264-128kbit_AAC).mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 64.3 MiB
Duration : 2 min 53 s
Overall bit rate : 3 108 kb/s
Movie name : HIS DARK MATERIALS Trailer (2019)
Performer : KinoCheck International
Recorded date : 2019
Writing application : Lavf58.39.101
Comment : https://www.youtube.com/watch?v=lGlGK3O4EXw
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 2 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 2 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 2 min 53 s
Bit rate : 2 975 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.057
Stream size : 61.5 MiB (96%)
Title : ISO Media file produced by Google Inc.
Writing library : x264 core 155 r2901 7d0ff22
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 : 2 min 53 s
Bit rate mode : Constant
Bit rate : 128 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 2.65 MiB (4%)
Title : ISO Media file produced by Google Inc.
Language : English
Default : Yes
Alternate group : 1
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