What's wrong with Plex on my DS918+?

Plex Media Server NAS & Devices
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Full qualification:

  1. H.264, H.265 hardware transcoding - ZERO problems.
  2. Image based subtitles (PGS, VOBSUB, etc) merging onto the HW transcoded video image is not supported by the internal ASIC.
  3. Merging (burning) subtitles into the image is a CPU function. This is true regardless of the CPU. This is true even of an I7-7700 CPU . The J3455 CPU does not have enough CPU Passmarks to burn the subtitles into the video image in Real -Time.
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Ok, that clears it up a bit for me. But still for the third point, there are qualifiers correct? I’m pretty sure the 918+ can transcode up to 1080p without problems.

Maybe I’m missing a technical detail here, but in my mind transcoding is transcoding. If Plex transcodes a source to 1080p, it needs to rebuild it frame by frame. Whether that new frame contains subs does not matter significantly to performance.

Am I mistaken in that assumption? Is there a difference in burning in srt as opposed to other image based formats (if set to ALWAYS burn subs of course)?

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The DS918+ (J3455 CPU) can decode H.265 and H.264 up to and including 2160p HDR.

Each frame is output from the ASIC one at a time. PMS adds subtitless, when instructed, to each frame prior to transmitting to the player.

All Plex Players support overlaying Text based subtitles in the player itself. These include SRT, ASS, and SSA formats. PMS transmits these subtitle streams as an independent, third, stream to the player (Video, Audio, text subitle).

Setting Burn = ALWAYS mandates the CPU merge the two streams prior to sending to the player. This causes undue waste of CPU and, in the case of the J3455 CPU, failure to playback smoothly. The best setting for subtitles is the default “AUTOMATIC”.

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Did some more testing with my DS918+ today. Here’s the things I tried on local 5Ghz Wi-fi (mediainfo attached).mediainfo.txt (3.4 KB)
19:59 - Tried to start file on my “iPad 2018”, iOS12. Spinner.
20:06 - I aborted it, the spinner was still spinning.
20:09 - Tried again, same file, same Ipad. Spinner
20:13 - I aborted it, the spinner was still spinning
20:19 - Tried the same file on my “iPhone XS”
20:20 - File actually started to play (after waiting a minute or so).
20:23 - I manually stopped the playback
20:28 - Tried again on my iPad…
20:35 - … but the spinner keeps spinning. I aborted it.

I have Plex-logs but since they contain personal information information I don’t want to share them here. I doubt they will give any new information either (I’ve posted many logs to admins previously) but let me know if anyone’s interested.
I’m desperately trying to understand the behaviour on what’s wrong on my setup but the pieces of the puzzle just don’t match eachother…

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I’m sorry but I am not equipped to help with app (iOS) issues here however this sounds entirely like a DNS rebinding / firewall / network issue.

As stated above, issue was reported to the iOS team for further investigation.

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A local PMS on Windows 10 seems to work perfect, on the very same network… If the problem is network-related, where should I start to look?

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Synology firewall and DEBUG (not verbose) logfiles which capture the attempt.
From the logs, PMS interaction can be seen.
Supplemental are:

  1. device playback settings - inclusive of subtitles (always burn, automatic, or only image formats)
  2. XML of the media being played.

An iPhone XR, with a smaller Synology DS1815+, doesn’t stall. Therefore it has to be in the media and how it’s being played unless, as previously forwarded to engineering, something particular to the XS geometry

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I’m not using the Synology firewall.

Tried today to connecting my NAS directly to my fiber-converter, bypassing my ASUS router, and playing with Plex through 4G on my iPhone.
Plex on my phone alerted me something about there wasn’t a “direct connection available to the server so the quality would be limited”, or something like that. But playback worked everytime (however, limited to 720xXXX resolution at 1-2mbps or something, no matter what quality settings I set).

So, what can this result tell us? Is it port-forwarding related perhaps since my router isn’t there to do that in my testcase.

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Got myself a new router today, Synology RT2600AC. Problems with Plex is still there, same as my previous router as far as I can see, there goes my theory something was bad about my ASUS router… :confused:

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Not sure what I’ve done but now everything works perfectly, all the time! I know the Plex-app had an update awhile ago with some router-related-fixes, not sure if that fixed it or something else I did. I reinstalled lots of apps on my NAS, not sure if that did the trick either.
So, problem solved. Not sure why sadly but it works now. :slight_smile:

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