Server Version#: 1.41.8.9834
Player Version#: All (LG, Android, Android TV tested)
I have SYNOLOGY DS423+
I have enabled HEVC transcoding. It works ok until I get subtitles burned. It is buffering every couple seconds. Why? The CPU usage is about 10%.
What is the input bitrate of the video.
How much memory is installed in the machine?
The GLK CPU (J4125) in the DS423+ has internal bandwidth performance limits and runs best with the max of 8GB of RAM (2x 4GB matching sticks)
I have added 2 sticks with 4GB so I have 10GB total:
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: None
Maximum Capacity: 8 GB
Error Information Handle: No Error
Number Of Devices: 2
Handle 0x0021, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0020
Error Information Handle: No Error
Total Width: 64 bits
Data Width: 64 bits
Size: 8192 MB
Form Factor: SODIMM
Set: None
Locator: ChannelA-DIMM0
Bank Locator: BANK 0
Type: DDR4
Type Detail: Synchronous Unbuffered (Unregistered)
Speed: 2400 MT/s
Manufacturer: Samsung
Serial Number: 412307B8
Asset Tag:
Part Number: M471A1K43CB1-CTD
Rank: 1
Configured Memory Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
Handle 0x0022, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0020
Error Information Handle: No Error
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: Row Of Chips
Set: None
Locator: ChannelB-DIMM0
Bank Locator: BANK 1
Type: DDR4
Type Detail: Synchronous Unbuffered (Unregistered)
Speed: 2400 MT/s
Manufacturer: Synology
Serial Number: 00000000
Asset Tag:
Part Number:
Rank: 1
Configured Memory Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
The video bitrate is ≈ 28,6 Mbps. It is 4k DV and i try tro transcode to 1080p 12 or 8MBps.
The J4125 only supports 8GB.
YES, DSM will read the chips and show you 10 but dual channel memory only works when all chips are the same.
The factory 2GB should be removed.
Move the 8GB to where the 2GB was
-or- (better)
use 2x 4GB matching memory sticks (enables dual channel memory mode)
Can you show me the media info for that movie ? I wonder how many unnecessary tracks are in the file. and which DV profile it is.
Actually I was wrong in first post. I have one additional 8GB stick (SAMSUNG 8GB DDR4 2400MHZ) and 2GB is build in originally so I think it is not removable.
Media info:
Format : Matroska
Format version : Version 4
File size : 18.0 GiB
Duration : 1 h 40 min
Overall bit rate : 25.6 Mb/s
Encoded date : UTC 2025-05-13 06:58:58
Writing application : mkvmerge v83.0 ('Circle Of Friends') 64-bit
Writing library : libebml v1.4.5 + libmatroska v1.7.1
Video
ID : 1
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main 10@L5@High
HDR format : Dolby Vision, Version 1.0, dvhe.08.06, BL+RPU, HDR10 compatible / SMPTE ST 2094 App 4, Version 1, HDR10+ Profile B compatible
Codec ID : V_MPEGH/ISO/HEVC
Duration : 1 h 40 min
Bit rate : 24.2 Mb/s
Width : 3 840 pixels
Height : 2 076 pixels
Display aspect ratio : 1.85:1
Frame rate mode : Constant
Frame rate : 23.976 FPS
Color space : YUV
Chroma subsampling : 4:2:0 (Type 2)
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.127
Stream size : 17.0 GiB (94%)
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primar : BT.2020
Mastering display luminance : min: 0.0050 cd/m2, max: 1000 cd/m2
Maximum Content Light Level : 1269 cd/m2
Maximum Frame-Average Light Le : 526 cd/m2
Audio #1
ID : 2
Format : E-AC-3
Format/Info : Enhanced AC-3
Commercial name : Dolby Digital Plus
Codec ID : A_EAC3
Duration : 1 h 40 min
Bit rate mode : Constant
Bit rate : 640 kb/s
Channel(s) : 6 channels
Channel layout : L R C LFE Ls Rs
Sampling rate : 48.0 kHz
Frame rate : 31.250 FPS (1536 SPF)
Compression mode : Lossy
Stream size : 462 MiB (2%)
Title : Polish
Language : Polish
Service kind : Complete Main
Default : Yes
Forced : No
Audio #2
ID : 3
Format : E-AC-3 JOC
Format/Info : Enhanced AC-3 with Joint Object Coding
Commercial name : Dolby Digital Plus with Dolby Atmos
Codec ID : A_EAC3
Duration : 1 h 40 min
Bit rate mode : Constant
Bit rate : 768 kb/s
Channel(s) : 6 channels
Channel layout : L R C LFE Ls Rs
Sampling rate : 48.0 kHz
Frame rate : 31.250 FPS (1536 SPF)
Compression mode : Lossy
Stream size : 554 MiB (3%)
Title : English
Language : English
Service kind : Complete Main
Default : No
Forced : No
Complexity index : 16
Number of dynamic objects : 15
Bed channel count : 1 channel
Bed channel configuration : LFE
Text #1
ID : 4
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Duration : 1 h 38 min
Bit rate : 0 b/s
Frame rate : 0.002 FPS
Count of elements : 10
Stream size : 226 Bytes (0%)
Title : Polish [Forced]
Language : Polish
Default : Yes
Forced : Yes
Text #2
ID : 5
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Duration : 1 h 39 min
Bit rate : 49 b/s
Frame rate : 0.234 FPS
Count of elements : 1402
Stream size : 36.0 KiB (0%)
Title : Polish
Language : Polish
Default : No
Forced : No
Text #3
ID : 6
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Duration : 1 h 39 min
Bit rate : 57 b/s
Frame rate : 0.259 FPS
Count of elements : 1548
Stream size : 42.2 KiB (0%)
Title : English
Language : English
Default : No
Forced : No
The memory specifications for the DS423+ is 6GB maximum, 2GB Internal (non-removable) plus a maximum 4GB additional.
The NAS will use your 8GB stick, but it is NOT optimal.
I would recommend that you re-encode that file using Handbrake to H.264/AAC. It should then Direct Play without any need to transcode the file.
Thats not the point. I dont want to encode every single movies and tv show to lower quality 
I am just wondering why subtitle burning cause buffering (transcoding without subtitles seems to work ok).
Burning subtitles in most cases is a single core process. There is working going on to improve that.
I there any option do disable burning on server for all users?
Yes, but it won’t force a direct play. If the client thinks the codecs aren’t support, they just won’t play.
It’s a server setting.
Disable video stream transcoding
Yeah… I have tried this but users that were transcoding before get ‘codecs aren’t support’ error instead of getting direct stream.
Need server DEBUG Logs to see this happening please.
That’s expected of you turn off transcoding. Unfortunately there isn’t a way to turn off burning in subtitles from the server side.
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