The video-only remux I added to my plex library takes a long time to play back in the plex web client. I am consistently getting a very long delay between clicking play and when the movie actually starts. Testing other movies in my library, so far this seems to be the only one with this delay (others start within a second of clicking play).
During the delay, the web client is just showing me a full-screen dimmed poster for the movie with a spinner over it.
During the delay, the server starts up a Transcoder process which runs for ~20 seconds, then goes away. About a minute to a minute and a half after that, the movie finally starts playing back as a second Transcoder process starts up.
Meanwhile the scanner process is still running in the background, still with the same pid.
Looking in the Plex Media Scanner.log file, I see some FFMPEG errors:
Feb 23, 2020 14:20:46.103 [0x7f8b7339f700] INFO - Plex Media Scanner v1.18.7.2438-f342a5a43 - Ubuntu PC x86_64 - build: linux-x86_64 - GMT 00:00
Feb 23, 2020 14:20:46.103 [0x7f8b7339f700] INFO - Linux version: 18.04.4 LTS (Bionic Beaver), language: en-US
Feb 23, 2020 14:20:46.103 [0x7f8b7339f700] INFO - Processor AMD EPYC Processor (with IBPB)�☺�☺�☺�☺@☺☻@@☺☻@(0
Feb 23, 2020 14:20:46.104 [0x7f8b7339f700] INFO - /usr/lib/plexmediaserver/Plex Media Scanner --scan --refresh --section 1 --activity b11ccd2c-ddb4-49d2-9f4a-c853837d170d
Feb 23, 2020 14:22:07.545 [0x7f8b68c24700] ERROR - [FFMPEG] - cabac decode of qscale diff failed at 25 12
Feb 23, 2020 14:22:07.545 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 25 12, bytestream 32531
Feb 23, 2020 14:22:07.549 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 904 DC, 904 AC, 904 MV errors in P frame
Feb 23, 2020 14:24:43.735 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 57 34, bytestream -32
Feb 23, 2020 14:24:43.736 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 880 DC, 880 AC, 880 MV errors in P frame
Feb 23, 2020 14:25:15.673 [0x7f8b68c24700] ERROR - [FFMPEG] - left block unavailable for requested intra4x4 mode -1
Feb 23, 2020 14:25:15.673 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 0 22, bytestream 3140
Feb 23, 2020 14:25:15.676 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 129 DC, 129 AC, 129 MV errors in P frame
Feb 23, 2020 14:29:49.530 [0x7f8b68c24700] ERROR - [FFMPEG] - Reference 3 >= 3
Feb 23, 2020 14:29:49.530 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 40 27, bytestream 28372
Feb 23, 2020 14:29:49.532 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 569 DC, 569 AC, 569 MV errors in P frame
Feb 23, 2020 14:30:09.928 [0x7f8b68c24700] ERROR - [MI] Read to end of file without finding a keyframe
Feb 23, 2020 14:30:09.962 [0x7f8b68c24700] ERROR - [FFMPEG] - mmco: unref short failure
Feb 23, 2020 14:30:09.962 [0x7f8b68c24700] ERROR - [FFMPEG] - mmco: unref short failure
Feb 23, 2020 14:31:18.880 [0x7f8b68c24700] ERROR - [FFMPEG] - cabac decode of qscale diff failed at 25 12
Feb 23, 2020 14:31:18.880 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 25 12, bytestream 32531
Feb 23, 2020 14:31:18.884 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 904 DC, 904 AC, 904 MV errors in P frame
Feb 23, 2020 14:33:59.632 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 57 34, bytestream -32
Feb 23, 2020 14:33:59.634 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 880 DC, 880 AC, 880 MV errors in P frame
Feb 23, 2020 14:34:32.297 [0x7f8b68c24700] ERROR - [FFMPEG] - left block unavailable for requested intra4x4 mode -1
Feb 23, 2020 14:34:32.297 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 0 22, bytestream 3140
Feb 23, 2020 14:34:32.301 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 129 DC, 129 AC, 129 MV errors in P frame
Feb 23, 2020 14:39:09.762 [0x7f8b68c24700] ERROR - [FFMPEG] - Reference 3 >= 3
Feb 23, 2020 14:39:09.762 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 40 27, bytestream 28372
Feb 23, 2020 14:39:09.764 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 569 DC, 569 AC, 569 MV errors in P frame
Feb 23, 2020 14:39:29.832 [0x7f8b68c24700] ERROR - [MI] Read to end of file without finding a keyframe
Feb 23, 2020 14:39:29.908 [0x7f8b68c24700] ERROR - [FFMPEG] - mmco: unref short failure
Feb 23, 2020 14:39:29.908 [0x7f8b68c24700] ERROR - [FFMPEG] - number of reference frames (0+6) exceeds max (5; probably corrupt input), discarding one
Feb 23, 2020 14:39:29.920 [0x7f8b68c24700] ERROR - [FFMPEG] - mmco: unref short failure
Feb 23, 2020 14:40:29.721 [0x7f8b68c24700] ERROR - [FFMPEG] - cabac decode of qscale diff failed at 25 12
Feb 23, 2020 14:40:29.721 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 25 12, bytestream 32531
Feb 23, 2020 14:40:29.725 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 904 DC, 904 AC, 904 MV errors in P frame
Feb 23, 2020 14:43:11.015 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 57 34, bytestream -32
Feb 23, 2020 14:43:11.016 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 880 DC, 880 AC, 880 MV errors in P frame
Feb 23, 2020 14:43:42.964 [0x7f8b68c24700] ERROR - [FFMPEG] - left block unavailable for requested intra4x4 mode -1
Feb 23, 2020 14:43:42.964 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 0 22, bytestream 3140
Feb 23, 2020 14:43:42.968 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 129 DC, 129 AC, 129 MV errors in P frame
Feb 23, 2020 14:48:14.395 [0x7f8b68c24700] ERROR - [FFMPEG] - Reference 3 >= 3
Feb 23, 2020 14:48:14.395 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 40 27, bytestream 28372
Feb 23, 2020 14:48:14.397 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 569 DC, 569 AC, 569 MV errors in P frame
Feb 23, 2020 14:48:34.522 [0x7f8b68c24700] ERROR - [MI] Read to end of file without finding a keyframe
Feb 23, 2020 14:49:56.672 [0x7f8b68c24700] ERROR - [FFMPEG] - cabac decode of qscale diff failed at 25 12
Feb 23, 2020 14:49:56.672 [0x7f8b68c24700] ERROR - [FFMPEG] - error while decoding MB 25 12, bytestream 32531
Feb 23, 2020 14:49:56.676 [0x7f8b68c24700] INFO - [FFMPEG] - concealing 904 DC, 904 AC, 904 MV errors in P frame