Some movies can't be optimized with no reason (message "Unable to convert"). Example below.
Ubuntu: 15.10, plex 0.9.15.0.
From logs:
Jan 05, 2016 17:51:03 [0x7fa3cbff5700] WARN - WARNING: Couldn't create directory /media/data/videos/_Unwatched/The Martian (2015)/Plex Versions/Optimized for Mobile/.inProgress
(...)
Jan 05, 2016 17:51:03 [0x7fa3d9bfd700] ERROR - [Transcoder] Could not write header for output file #6 (incorrect codec parameters ?): Invalid argument
Directory:
drwxr-sr-x 2 plex xxx 4096 Jan 5 17:51 Plex Versions
$ tree Plex\ Versions/
Plex Versions/
0 directories, 0 files
mediainfo:
Format : Matroska
Format version : Version 4 / Version 2
File size : 4.70 GiB
Duration : 2h 21mn
Overall bit rate : 4 744 Kbps
Writing application : mkvmerge v8.3.0 ('Over the Horizon') 64bit
Writing library : libebml v1.3.1 + libmatroska v1.4.2
Attachements : cover_land.jpg / small_cover.jpg / small_cover_land.jpg / cover.jpg
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings, CABAC : Yes
Format settings, ReFrames : 5 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 2h 21mn
Bit rate : 4 265 Kbps
Width : 1 916 pixels
Height : 796 pixels
Display aspect ratio : 2.40:1
Frame rate mode : Constant
Frame rate : 23.976 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.117
Stream size : 4.22 GiB (90%)
Language : English
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Audio
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 2h 21mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 389 MiB (8%)
Language : English
Default : Yes
Forced : No
Text
ID : 3
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Language : English
Default : Yes
Forced : No