Don't pick highest quality when transcoding down

Plex Media Server
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Currently, Plex will auto-select the highest quality when transcoding content to match the client’s requests.

For example, If I have 4K, 1080p, 720p, SD versions of an item and a client attempts to play something have has a bandwidth limit say 2Mbps (which is the current default in all clients)

I have the following:

15.5 Mbps, 4K
6.9 Mbps, 1080p
2.6 Mbps, 720p
1.3 Mbps, SD

Instead of Playing the SD Version which is 1.3Mbps, it will transcode the 4K version down to 2Mbps …

In my scenario, the user had a limit of 10Mbps and the player decided to serve the 4K 15.5Mbps instead of the 1080p 6.9Mbps and to transcode the 4K file down to 10Mbps 1080p.

While I don’t usually care about transcoding I keep multiple versions to avoid transcoding especially 4K to a lower quality transcoding - however, the server currently makes that pointless as it will always try to transcode the highest possible value even if it 4K when there are multiple better-suited version to use as the source for transcoding.

This seems like a pretty common sense behavior why transcode the highest available instead of player the lowest compatible version without the need to transcode - if all files need to be transcoded to the client then the server should transcode the content that most closely matches the final resolution i.e, in this case, Play the 6.9Mbps 1080p entry if not possible to play it or the 720p or the SD version then if the client limit is 10Mbps transcode the 1080p version NOT the 4K version which is already above the client’s bitrate limit.

1 Like
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According to @ ChuckPa here the current behaviour is a bug.

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This is definitely a bug at the moment. I’m not sure if it’s a recent player problem or Plex Media Server issue, but prior to the beginning of the year, it correctly selected the appropriate version to transcode to your desired quality.

So choosing to transcode media to 8Mbps 1080p would select the 1080p version to transcode (or direct play) from, and not the 4k copy.

As it stands, if someone has a 4k capable TV, but haven’t set their quality settings, or choose go lower, its transcoding the damn 4k copy down. If you have a full HD TV, only then does it choose the 1080p copy.

For a long time now we haven’t had to use separate libraries because the Plex Streaming Brain has been able to work it out accordingly. But it’s broken at the moment.

@ChuckPa Are you seeing this behaviour also?

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Can you please provide your server logs after playing something that does this and if you can the xml info from the media item you played.

Something already being investigated and I would like to add more logs to bug report

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Yep, I’ll grab some logs later. I’m just about to go out, but I’ll do it as soon as I get home in a few hours.

Edit -
Sent :wink:.

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So I’ve recently started to experience this problem myself. I posted about it on Reddit here and got an awful lot of community feedback - which is great!

I’ve since done a little bit more experimenting and found the following.

For the tests in question I was using a PS4 Slim (which doesn’t support 4K) connected to a 1080p TV.

TEST 1
Movie with the below two files:

  • 24.3Mbps 4K
  • 14.4Mbps 1080p

With quality set to Original on the PS4, Plex direct streams the 1080p file due to audio incompatibility - as expected for a 1080p device/monitor.

With quality set to 1080p 20Mbps on the PS4, interestingly it doesn’t direct stream, but instead it transcodes using the 1080p file as the source. I’d expect the same direct stream here given the bitrate, but ok.

Here’s where things go wrong. With quality set to 1080p 12Mbps or lower on the PS4, Plex transcodes the video using the 4K version as the source.

TEST 2
Movies with the below two files:

  • 15.2Mbps 4K
  • 7.4Mbps 1080p

With quality set to Original on the PS4, Plex direct streams the 1080p file due to audio incompatibility - as I would expect for a 1080p device/monitor. Same as TEST 1.

With quality set to 1080p 20Mbps on the PS4, I get the same direct stream as with original settings.

With quality set to 1080p 12Mbps, 1080p 10Mbps, or 1080p 8Mbps on the PS4, we see behaviour similar to TEST1. It doesn’t direct stream, but instead it transcodes using the 1080p file as the source. I’d expect the same direct stream here given the bitrate, but ok.

Again, this is where it gets interesting! With quality set to 720p 4Mbps or lower, Plex transcodes the video using the 4K version as the source.

Conclusion

There’s definitely something wrong here in the transcode decision process. It seems to me that the check is backwards. As it only transcodes the 4K version when the quality bitrate is set to LESS THAN the bitrate of the 1080p file.

Let me know if logs will help, happy to provide.

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yes please

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Sent!

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is your 4K file HDR?

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Sorry I just came back to see if there was any response as I’m still seeing the issue and noticed your question @BigWheel. Yes the files are HDR.

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OK thank you. Unfortunately devs have not figured out issue yet.

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I’m still seeing the issue quite regularly

This movie has the below two files available
image

but some clients are still transcoding the 4K version down to 720p instead of using the 1080p version. Not limited to just the PS4 client either.
image

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