OK, correction... seems only a couple of my files are not playing, sorry. The rest do indeed play through Channels. But there are weird video lengths listed. E.g. one file is reported as -3346 (min. I presume?) in the Channels app, 0 sec in the WebUI, and 48 min. when I view the file details in the WebUI. Strange.
I am getting things like this in the logs:
2021/09/10 12:39:32.957485 [ENC] Starting encoder for Debris - s01e13 - Celestial Body.mp4 in /media/DVR/Streaming/file463-ip192.168.254.65-892212060/encoder-0-796432139 at 0 (0.000000) (encoder=remux, resolution=720, deinterlacer=, bitrate=10000 segment_size=0.01)
2021/09/10 12:39:33.413167 [HLS] ffmpeg: file463-ip192.168.254.65: [mov,mp4,m4a,3gp,3g2,mj2 @ 0x2d4b5db0] stream 0, timescale not set
2021/09/10 12:39:33.634266 [HLS] ffmpeg: file463-ip192.168.254.65: [mov,mp4,m4a,3gp,3g2,mj2 @ 0x2d4b5db0] Could not find codec parameters for stream 3 (Video: png, none): unspecified size
2021/09/10 12:39:33.634397 [HLS] ffmpeg: file463-ip192.168.254.65: Consider increasing the value for the 'analyzeduration' and 'probesize' options
2021/09/10 12:39:42.408607 [ENC] Stopped encoder for Debris - s01e13 - Celestial Body.mp4 in /media/DVR/Streaming/file463-ip192.168.254.65-892212060/encoder-0-796432139 after encoding 0 to 150
2021/09/10 12:47:45.309294 [ERR] Failed to probe file Debris/Season 1/Debris - s01e08 - Spaceman.mp4: exit status 1
2021/09/10 12:47:55.958177 [IDX] Generating video index for file-285: Debris - s01e09 - Do You Know Icarus_.mp4
2021/09/10 12:50:39.392309 [ERR] Generating video index for file-285 failed: No Keyframes were found in the stream