4k Transcode stuttering

[andcbii]

Server Version#: Version Version 1.29.1.6316
Player Version#: WEB: Version 4.87.2 iOS 8.11.1

I have a Intel i7-8700K with a nvidia P2000. I’m trying to transcode a 4k file down to 1080p (8Mbps -20Mbps) and the video stutters every couple of seconds. In task manager the CPU, disk, and GUP are all well under 100% utilization. Emby is able to play the same files with out stuttering, so I don’t think it’s an issue with my hardware (or lack of hardware power). Any idea why plex would be stuttering?

Video:

Video
ID                                       : 1
ID in the original source medium         : 4113 (0x1011)
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main 10@L5.1@High
HDR format                               : Dolby Vision, Version 1.0, dvhe.07.06, BL+EL+RPU, Blu-ray compatible / SMPTE ST 2086, HDR10 compatible
Codec ID                                 : V_MPEGH/ISO/HEVC
Duration                                 : 2 h 23 min
Bit rate                                 : 54.8 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 23.976 (24000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0 (Type 2)
Bit depth                                : 10 bits
Bits/(Pixel*Frame)                       : 0.276
Stream size                              : 54.9 GiB (70%)
Language                                 : English
Default                                  : No
Forced                                   : No
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                 : PQ
Matrix coefficients                      : BT.2020 non-constant
Mastering display color primaries        : Display P3
Mastering display luminance              : min: 0.0050 cd/m2, max: 4000 cd/m2
Maximum Content Light Level              : 1506 cd/m2
Maximum Frame-Average Light Level        : 459 cd/m2
Original source medium                   : Blu-ray

Audio #1
ID                                       : 2
ID in the original source medium         : 4352 (0x1100)
Format                                   : MLP FBA 16-ch
Format/Info                              : Meridian Lossless Packing FBA with 16-channel presentation
Commercial name                          : Dolby TrueHD with Dolby Atmos
Codec ID                                 : A_TRUEHD
Duration                                 : 2 h 23 min
Bit rate mode                            : Variable
Bit rate                                 : 3 579 kb/s
Maximum bit rate                         : 6 144 kb/s
Channel(s)                               : 8 channels
Channel layout                           : L R C LFE Ls Rs Lb Rb
Sampling rate                            : 48.0 kHz
Frame rate                               : 1 200.000 FPS (40 SPF)
Bit depth                                : 24 bits
Compression mode                         : Lossless
Stream size                              : 3.58 GiB (5%)
Title                                    : Surround 7.1
Language                                 : English
Default                                  : Yes
Forced                                   : No
Original source medium                   : Blu-ray
Number of dynamic objects                : 15
Bed channel count                        : 1 channel
Bed channel configuration                : LFE

I thought it could be an DolbyVision to SDR issue but it also happens with this file:

Video
ID                                       : 1
ID in the original source medium         : 4113 (0x1011)
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main 10@L5.1@High
HDR format                               : SMPTE ST 2086, HDR10 compatible
Codec ID                                 : V_MPEGH/ISO/HEVC
Duration                                 : 1 h 58 min
Bit rate                                 : 43.9 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 23.976 (24000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0 (Type 2)
Bit depth                                : 10 bits
Bits/(Pixel*Frame)                       : 0.221
Stream size                              : 36.2 GiB (77%)
Writing library                          : ATEME Titan File 3.8.16 (4.8.16.0)      
Language                                 : English
Default                                  : No
Forced                                   : No
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                 : PQ
Matrix coefficients                      : BT.2020 non-constant
Mastering display color primaries        : Display P3
Mastering display luminance              : min: 0.0001 cd/m2, max: 1000 cd/m2
Original source medium                   : Blu-ray

Audio #1
ID                                       : 2
ID in the original source medium         : 4352 (0x1100)
Format                                   : MLP FBA 16-ch
Format/Info                              : Meridian Lossless Packing FBA with 16-channel presentation
Commercial name                          : Dolby TrueHD with Dolby Atmos
Codec ID                                 : A_TRUEHD
Duration                                 : 1 h 58 min
Bit rate mode                            : Variable
Bit rate                                 : 4 746 kb/s
Maximum bit rate                         : 7 335 kb/s
Channel(s)                               : 8 channels
Channel layout                           : L R C LFE Ls Rs Lb Rb
Sampling rate                            : 48.0 kHz
Frame rate                               : 1 200.000 FPS (40 SPF)
Bit depth                                : 24 bits
Compression mode                         : Lossless
Stream size                              : 3.92 GiB (8%)
Title                                    : Surround 7.1
Language                                 : English
Default                                  : Yes
Forced                                   : No
Original source medium                   : Blu-ray
Number of dynamic objects                : 13
Bed channel count                        : 1 channel
Bed channel configuration                : LFE

[FordGuy61]

If you’ve not already done so, install the 64-bit version of Plex Media Server for Windows (download from plex.tv). It supports zero-copy hardware transcoding with Nvidia GPUs. It may help with transcoding and tonemapping HDR video.

You can install the 64-bit version on top of the 32-bit version. The 64-bit installer will recognize the 32-bit installation and remove it from your server. This affects only the Plex binaries, not the Plex Media Folder nor your media.

If you roll back, note that the reverse is not true. The 32-bit installer is not aware of the 64-bit version. You will need to manually uninstall the 64-bit version using the standard Windows uninstaller (do not use Revo, CCleaner, etc). Then install the 32-bit version.

Transcoding Dolby Vision

Plex cannot transcode Dolby Vision video. It has no license to do so from Dolby.

If the video contains a HDR10 layer, Plex will transcode the HDR10 layer instead.

If the video does not contain a HDR10 layer, such as DV profile 5, Plex will return a “color space not supported” error.

Transcoding HDR10

On Windows based systems, Plex has very limited support for tonemapping HDR video to SDR video when transcoding. There is limited support for Intel GPUs and no support for Nvidia GPUs.

With a Nvidia GPU in the system, Plex will use the GPU to transcode the video (if hardware transcoding is enabled). However, it will use the CPU for tonemapping.

Reference: HDR to SDR Tone Mapping

Transcoding on Windows with an Nvidia GPU

As of PMS v1.29.0.6219, the 64-bit version of Plex supports zero copy transcoding with Nvidia GPUs. This reduces the amount of data Plex must move between the GPU and system when transcoding video. This permits Plex to more efficiently transcode video.

Some users have reported the increase in transcoding efficiency has made it possible for Plex to transcode and tonemap on Windows based systems.

[andcbii]

@FordGuy61

d systems, Plex has very limited support for tonemapping HDR video to SDR video when transcoding. There is limited support for Intel GPUs and no support for Nvidia GPUs.

With a Nvidia GPU in the system, Plex will use the GPU to transcode the video (if hardware transcoding is enabled). However, it will use the CPU for tonemapping.

Reference: HDR to SDR Tone Mapping

Switching to 64 bit seems to have fixed the issue. Thanks a ton! This as been bugging me for a while now.

[kishkaru]

I had the exact same issue as the OP, and switching to the 64-bit PMS fixed the issue.

I upgraded to an Nvidia RTX A2000 6GB, and using the latest Nvidia studio drivers (517.40). My 4K transcodes were buffering every few seconds and it was unwatchable. I thought my GPU was defective, as I previously had a GTX 1050 3GB which had no issues transcoding 4K. Decode/encode GPU usage was around 15-20% like OP’s, and GPU-Z showed the card was mostly sleeping, and running at PCI-E x16 @ 1.1 (instead of 4.0).

Before:

After:

0.8x transcode speed to 6.7x
The above is with HDR tonemapping turned on. On/off doesn’t seem to make any difference for me for transcode speed or CPU usage.

And just for fun, CPU transcoding on my AMD Threadripper. Who need a GPU anyway