PMS transcoding SRT subtitles

Server Version#: 4.76.1
Player Version#: LG App WebOS

Hi everybody, I have a weird behavior with one mkv file. The file is composed with the video track, FLAC audio track and one subtitle track in SRT/TXT mode.

Everytime I select the subtitle track the PMS starts transcoding the video. I have lots of files with SRT tracks and these are displayed correctly without transcoding. I paste de mediainfo for the file:

General
Unique ID                                : 206923038649451457856346380095762986739 (0x9BABED79480B13CAF379638D1237F6F3)
Complete name                            : X:\XXXX\XXXX 1x01.mkv
Format                                   : Matroska
Format version                           : Version 4
File size                                : 1.04 GiB
Duration                                 : 22 min 52 s
Overall bit rate mode                    : Variable
Overall bit rate                         : 6 513 kb/s
Movie name                               : Given 1x01
Encoded date                             : UTC 2022-04-27 08:41:15
Writing application                      : mkvmerge v67.0.0 ('Under Stars') 64-bit
Writing library                          : libebml v1.4.2 + libmatroska v1.6.4

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L5
Format settings                          : CABAC / 5 Ref Frames
Format settings, CABAC                   : Yes
Format settings, RefFrames               : 5 frames
Codec ID                                 : V_MPEG4/ISO/AVC
Duration                                 : 22 min 52 s
Bit rate                                 : 5 269 kb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 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
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.106
Stream size                              : 862 MiB (81%)
Writing library                          : x264 core 157 r2935 545de2f
Encoding settings                        : cabac=1 / ref=5 / deblock=1:1:1 / analyse=0x3:0x113 / me=umh / subme=9 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=32 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=34 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / stitchable=1 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=240 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=16.0 / qcomp=0.65 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language                                 : Japanese
Default                                  : Yes
Forced                                   : No

Audio
ID                                       : 2
Format                                   : FLAC
Format/Info                              : Free Lossless Audio Codec
Codec ID                                 : A_FLAC
Duration                                 : 22 min 52 s
Bit rate mode                            : Variable
Bit rate                                 : 1 242 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 11.719 FPS (4096 SPF)
Bit depth                                : 24 bits
Compression mode                         : Lossless
Stream size                              : 203 MiB (19%)
Writing library                          : libFLAC 1.3.2 (UTC 2017-01-01)
Language                                 : Japanese
Default                                  : Yes
Forced                                   : No

Text
ID                                       : 3
Format                                   : UTF-8
Codec ID                                 : S_TEXT/UTF8
Codec ID/Info                            : UTF-8 Plain Text
Duration                                 : 20 min 27 s
Bit rate                                 : 48 b/s
Count of elements                        : 277
Stream size                              : 7.23 KiB (0%)
Title                                    : Español (completos)
Language                                 : Spanish
Default                                  : Yes
Forced                                   : No

Menu
00:00:00.000                             : :IntroducciĂłn
00:05:32.999                             : :Opening
00:07:02.964                             : :Episodio
00:21:06.056                             : :Ending
00:22:36.021                             : :Avance

Can you give me any clue why this is happening only with this file?

The original file had ASS subtitle track, and I have converted it to SRT, deleted the ASS track and reassembled the MKV with th SRT track.

Thanks in advanced.

I have two different LG TVs and can confirm that SRT subs play well on both (but not PGS or ASS, both of which trigger video transcodes to burn them in).

However, the LG web app is also incapable of playing FLAC audio, so that will be transcoded and remuxed.

Yes, I know the FLAC is transcoded. The problem is that the same Plex App on the same TV is transcoding this file when I switch on the subs and it’s not transcoding any other file with SRT subs, and I don’t know why, because I need the video not to be transcoded.

Do the other files have FLAC audio? Video transcodes tend to happen when subtitles are displayed and the audio is being transcoded.

Hi. while you were writting I tested to save the FLAC file to MP3 and now there’s no transcoding at all. Thanks a lot!!

1 Like

Yeah, I’ve seen similar behaviour. It’s a bit wasteful to do a video transcode in these circumstances when an audio transcode and remix is probably all that’s needed.

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