Minimal Transcoding Request (Not So Smart Transcoder)

Plex Media Server
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Server Version#: 4.69.1
Player Version# Latest on Google TV w/ Chromecast

Since I am a fan of UHD video but not so much of Surround sound, I have transcoded some of the audio in my video collection to down-mixed stereo (with some bias towards the center channel since otherwise the dialog is too low volume). Since some of my content is now in Dolby TrueHD, I figured I’d transcode it to stereo FLAC (lossless to lossless). Only when I tried to play this content on my Google TV (Android TV dongle) using Plex, it kept stalling. Some investigation revealed that the Plex server was transcoding both the audio and the video. Now, the FLAC audio may need transcoding, but the HEVC video does not. This is broken. Not only does playback suck in terms of stalling, but the video quality is significantly degraded. If I use an audio format supported on the on-device player (such as the original TrueHD audio or AC3), then playback is “fine” (but the dialog is weak / hard to hear). Anyhow, I guess this is a feature request to transcode only those streams which need transcoding to support playback on whatever client device, but just copy any supported audio / video streams.

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If you want to transcode a audio stream you also need to transcode the video stream to keep them in sync

3

Uh, no. Incorrect. You might have to re-mux them into the same container after transcoding one or more elementary streams. I’m not certain whether Plex delivers the streams separately or multiplexed together (I suspect the latter), but there is no need to transcode the video just because you transcode the audio, or vice-versa. Multiplexing the streams is much cheaper computationally than transcoding. By orders of magnitude.

4

Do the videos being transcoded have subtitles?

5

Yes. They do have subtitles.

6

That’ll likely be the reason for the transcode then. Try disabling the subtitles and see if it reverts to direct streaming the video and just transcoding the audio.

7

I fail to see the logic there. Why would it transcode the video just because there are subtitles present?

For the time being I have worked around the problem by transcoding the stereo audio back into TrueHD (MLP). Since it’s supported by the client, no transcoding occurs at all at playback time. However, the request still stands. I wonder how much unnecessary transcoding the Plex server currently engages in globally. You can both improve the user experience, and help save the planet a little bit by doing away with it.

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