Subtitle-related transcoding causes impossible stuttering

Plex Players Smart TVs
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Server Version#: 1.20.3.3483 (Win & Mac)
Player Version#: Platform 3.8, Player 5.2.1
TV: lg-49UJ635V (latest firmware 05.80.65)

For any direct play-supported video file, whenever my audio needs to be transcoded (HDMI-CEC-connected soundbar supports AC3 only: Sony HT-S20R), srt subtitles cause video to be transcoded too. This is bad enough (and hopefully could get fixed like it was in Android TV?).

But the much more serious issue, that prevents me from being able to watch anything with subtitles and non-AC3 audio, is that this causes the player to stutter constantly even if I drop the bitrate to ⅒ of the original (which itself plays directly no problem). If I turn subtitles off and force video transcoding manually, it plays fine. Subtitle burn-in settings makes no difference.

This happens on both Early Access and on old app. Happens with my Ryzen 3900X and GTX2070 on 1Gb ethernet and on a Macbook Pro on WiFi (completely different server). Happens irrespective on any combination of server settings that I have spent a full day exploring (Secure Connections Disabled, no IPV6, Make my CPU hurt, allow no auth). Happens whenever audio needs to be transcoded, irrespective of the original video quality. Happens on TV’s internal speakers (where I leave Plex’s allowed Audio format to be what I need: AC3 only).

Is that expected?! What can be done? Short of reencoding my whole library or learning French, Mandarin, Spanish, Thai, etc… will MiBox S sort this issue? Is there a way to roll-back to earlier version of Early Access (there were some changes to subtitle handling)? Why subtitles need to be burned in when only audio is transcoded? Why video transcoding without subtitles plays fine at much, much higher bitrates than when it also contains burned-in subtitles? Can I somehow force the 100% use of my 12-core CPU to just watch a movie?

I’m a bit at a loss, any suggestions welcomed! And if it’s not a bug and is unlikely to be ever fixed, I would love to know, too. Thank you.

Regards
m.

redacted log: Plex Transcoder Statistics.log (8.0 KB)

console constantly prints out:

Playback warning occurred. Reason: BufferingExcessive, Excessive buffering has been detected!
[PlaybackSessionController] playback state changed to: buffering
[PlaybackSessionController] playback state changed to: playing
[PlaybackSessionController] playback state changed to: buffering
[PlaybackSessionController] playback state changed to: playing
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[Edit] ~Just wanted to say they version 5.3.1 fixed constant buffering problem, thank you!~

I still would love to know how likely is it for WebOS app to not have to burn subtitles (and transcode video) when it’s transcoding audio…

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Actually, no. 5.3.1 hasn’t fixed anything. This (unnecessary!) transcoding starts to buffer like crazy every time one rewinds or fast forwards, shows menu(s) or resumes from title screen. Pausing seems safe, but I haven’t tested it too thoroughly.

Possibly related to LG webOS Plex 3.60.1 Buffering Problem or LG TV App Transcoding SRTs.

This has clearly nothing to do with the stress the transcoding incurs (even forgetting it’s not needed in the first place), but a bug in the app/server/whatever.

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I’m observing similar issues. Turning subtitles ON leads to disaster. Sound disappears, server crashes etc.

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Results I’m seeing here:

Direct Play for both audio and video, no subs: OK
Direct Play for both audio and video, SRT subs: OK
Direct Play for video, transcoded audio, no subs: low server CPU (audio transcoding only), playback fine
Direct Play for video, transcoded audio, SRT subs: both audio and video now transcoded, CPU through roof, continuous buffering

(tested with the preview release of the LG app)

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Yep, this is exactly my experience: whenever audio is transcoded, srt unnecessarily forces transcoding of video (which otherwise doesn’t require transcoding). When that happens, if I play the movie from the beginning and never rewind or fast forward or enter any menu that stops playback (subtitle choice, three dot menu), it may play OK (although video is still unnecessarily transcoded). Whenever I do anything of the above (or Resume play), I get constant buffering.

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I read a Plex staffer who stated that this was due to maintaining synchronisation of audio and subtitles with the stream tech available. Once the audio is transcoded, this sync is lost and baking the subtitles into the video stream directly is the only way to guarantee sync with audio. Yes, it’s daft (and annoying!) but I’m not sure what technical solutions are available at the moment.

Would love to see it fixed though as it’s bloomin’ annoying, especially with 4k content where transcoding is uber-expensive.

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Does it make any difference if the SRT subtitles are muxed into the original video file, vs. being sidecar files?

I have some vague memory that it matters on some TVs - maybe LG? Maybe Samsung? But I may be conflating issues, and I’m not finding the source thread(s) quickly now.

1 Like
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Good question and no: it makes no difference. Also checked it’s the same with pgs (which I guess genuinely force video transcode as opposed to srt, which shouldn’t and since recently do not on Android client).

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AFAIK, this was fixed in Android client 8.0.0, so, hopefully, can also be fixed in LG App. It would be good to know if this is something that the team is aware being a feature request.

Alternatively, if it’s completely impossible (or highly unlikely), it would be nice to know that too, so that I would know I have to buy eg. a MiBox to avoid unnecessary transcode. And to be able to fast forward, because playing the movie from the beginning every time I want to rewind is a bit too much :wink:

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Another related thread: Partially-Transcoded Direct Stream not working as designed

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Just an update on this, not really related to WebOS Preview, but to Plex in general. I hope it may be of use to someone.

So I bought Google Chromecast with Google TV gizmo to be able to fast forward and rewind movies with subtitles and an audio track incompatible with my AC3-only 5.1 soundbar.

After fighting with it forever (latest Android Plex app allows choosing only-AC3 only when one chooses Optical passthrough even though it’s a lie, because it’s all HDMI-CEC; for model numbers see OP), I finally got 5.1 sound working. But whether it’s transcoded or not, there is a lag with video of around 400ms. Hahaha. Ha. Huh?!

I guess it was a huge mistake to buy a soundbar with Dolby Digital only (AC3). Or believing Plex will transcode. Or believing HDMI CEC is grandmother-compatible. It might have been easier to do peek and poke on Atari 8bit than getting surround sound on this combo of hardware and software :man_facepalming:.

I may report this to Android Plex app forum, but not sure. Now I’m not even sure if I’m waiting for Plex to fix unnecessary transcoding of video when audio is transcoded, for Plex to fix rewind/fastforward in this situation or for Plex to fix Android app having audio sync problems… Just don’t tell me to buy NVidia Shield, OK? :wink:

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