If I may add here?
None of the Synology CPUs, except for the Xeon based ones, are any good at subtitle burning. They never have been.
I see in the above posts where the settings / decisions have been “burn”. This is the cause of the slow transcode speed.
What’s happening in Plex when burning subtitles:
For each video frame:
- HW decodes the input video and deposits in a buffer
- The CPU then constructs and merges the text overlay into the video image
- HW encodes the resultant video frame
That process of construction and merge is CPU intensive.
On Synology, the best path is to avoid subtitle burning at all cost.
Media curation, i.e. Burning desired subtitles into the video in advance externally will always yield the best result.
