Stuttering playback of Dolby Vision movies with PGSSUB subtitles

[TheColin21]

I have a problem with stuttering playback (looks like skipped frames to me) when I try to play Dolby Vision content with PGSSUB subtitles.

I am using an LG OLED B9 tv and I already opened an issue on GitHub, but I would like to know if anyone here has had similar issues and knows a workaround (besides disabling the subs).

If I disable the subs, the video gets played directly and works totally fine.
If they are enabled, the video is transcoded (I have hw transoding enabled with my Intel A310) to add the subs.

The TV then gets an SDR version that lags horribly, although CPU, GPU and RAM of my server are not used much.
ffmpeg also reports this many times: 

Code:

[hevc @ [color=#569cd6]0x55cf5753b0c0[/color]] Skipping NAL unit [color=#569cd6]63[/color]

Any ideas?

[TheDreadPirate]

Can you share your ffmpeg log? Are the PGS subs being burned in? Or did you enable experimental PGS sub rendering?

[TheColin21]

Can you share your ffmpeg log?  Are the PGS subs being burned in?  Or did you enable experimental PGS sub rendering?

Here are the logs.

I honestly don't know where I could enable experimental PGSSUB rendering.

[TheDreadPirate]

It is burning in the subtitles. AFAICT, the transcode is happening fast enough. But what I do see is a pretty high bit rate. How is your TV connected to your router?

[TheColin21]

It is burning in the subtitles.  AFAICT, the transcode is happening fast enough.  But what I do see is a pretty high bit rate.  How is your TV connected to your router?

Via 100Mbps Ethernet and Wifi. The movie is only 65Mbps though and if I play it without subs its perfectly smooth.

[TheDreadPirate]

If it is currently connected via Ethernet, switch to WiFi. TVs or notorious for including garbage Ethernet controllers on their TV that can't sustain their rated transfer speed. Even expensive TVs.

[TheColin21]

If it is currently connected via Ethernet, switch to WiFi.  TVs or notorious for including garbage Ethernet controllers on their TV that can't sustain their rated transfer speed.  Even expensive TVs.

I understand that, it does not explain the symptoms though.

I can stream the movie just fine via ethernet if I just disable the PGSSUBs and therefore get direct play.
The same goes for other files that are Dolby Vision with PGSSUBs.

I also tried streaming the movie with a bandwidth limit of 20Mbps, still did not improve.

[TheColin21]

Just had the problem again today.
4K HEVC DV Profile 8.1 with DTS-HD audio lagged like hell with PGS and VobSub subtitles but played like butter with SRT.

Is no one else facing this?