Thanks for the advice!
Have downloaded and installed mediainfo, and analysed one of my film purchases.
Subtitle format seems to be either TX3G or c608 (which I’m fairly certain is a closed caption file type).
Full text file below:
General
Complete name : /Volumes/Jon_Ext/Media/Films/Conversions/Doctor Strange (2016).mp4
Format : MPEG-4
Format profile : Base Media / Version 2
Codec ID : mp42 (mp42/isom)
File size : 4.35 GiB
Duration : 1h 55mn
Overall bit rate mode : Variable
Overall bit rate : 5 386 Kbps
Movie name : Doctor Strange (2016)
Performer : Scott Derrickson
Performer/Sorted by : Scott Derrickson
Director : Scott Derrickson
Actor : Benedict Cumberbatch / Chiwetel Ejiofor / Rachel McAdams / Benedict Wong / Michael Stuhlbarg / Benjamin Bratt / Scott Adkins / Mads Mikkelsen / Tilda Swinton / Zara Phythian / Alaa Safi / Katrina Durden / Topo Wresniwiro / Umit Ulgen / Linda Duan / Mark Anthony Brighton / Meera Syal / Amy Landecker / Adam Pelta-Pauls / Sarah Malin / Eben Young / Kobna Holdbrook-Smith / Elizabeth Healey / Guillaume Faure / Daniel Dow / Stan Lee / Ezra Khan / Kimberly Van Luin / Pat Kiernan
Screenplay by : Scott Derrickson / Jon Spaihts / C. Robert Cargill
Producer : Kevin Feige
Production studio : Marvel
Genre : Action & Adventure
ContentType : Short Film
Description : From Marvel comes Doctor Strange, the story of world-famous neurosurgeon Dr. Stephen Strange, whose
Recorded date : UTC 2017-02-28 08:00:00
Encoded date : UTC 2017-02-15 17:33:27
Tagged date : UTC 2017-02-15 19:13:00
Copyright : © 2016 Marvel
Cover : Yes
Rating : None
Title/Sort : Doctor Strange (2016)
LongDescription : From Marvel comes Doctor Strange, the story of world-famous neurosurgeon Dr. Stephen Strange, whose life changes forever after a horrific car accident robs him of the use of his hands. When traditional medicine fails him, he is forced to look for healing, and hope, in an unlikely place – a mysterious enclave known as Kamar-Taj. He quickly learns that this is not just a center for healing but also the front line of a battle against unseen dark forces bent on destroying our reality. Before long Strange – armed with newly acquired magical powers – is forced to choose whether to return to his old life or leave it all behind to defend the world as the most powerful sorcerer in existence.
PurchaseDate : 2017-02-15 16:37:39
AppleStoreCountry : United States
AppleStoreCatalogID : 1164294784
GenreID : 4401
ContentRating : mpaa|PG-13|300|for sci-fi violence and action throughout, and an intense crash sequence.
Video
ID : 6
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings, CABAC : Yes
Format settings, ReFrames : 2 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1h 55mn
Bit rate mode : Variable
Bit rate : 4 501 Kbps
Maximum bit rate : 768 Kbps
Width : 1 920 pixels
Height : 804 pixels
Display aspect ratio : 2.40:1
Frame rate mode : Variable
Frame rate : 23.976 fps
Minimum frame rate : 23.077 fps
Maximum frame rate : 35.294 fps
Original frame rate : 25.000 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.122
Stream size : 3.63 GiB (84%)
Language : English
Encoded date : UTC 2017-02-15 18:07:50
Tagged date : UTC 2017-02-15 19:12:35
Audio #1
ID : 1
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 124 Kbps
Maximum bit rate : 215 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Frame rate : 46.875 fps (1024 spf)
Compression mode : Lossy
Stream size : 102 MiB (2%)
Language : English
Default : Yes
Alternate group : 1
Encoded date : UTC 2017-02-15 17:33:28
Tagged date : UTC 2017-02-15 17:40:35
Menus : 14
Audio #2
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : ac-3
Duration : 1h 54mn
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
Frame rate : 31.250 fps (1536 spf)
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 316 MiB (7%)
Language : English
Default : No
Alternate group : 1
Encoded date : UTC 2017-02-15 17:40:36
Tagged date : UTC 2017-02-15 17:46:13
Audio #3
ID : 3
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 125 Kbps
Maximum bit rate : 197 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Frame rate : 46.875 fps (1024 spf)
Compression mode : Lossy
Stream size : 103 MiB (2%)
Language : French
Default : No
Alternate group : 1
Encoded date : UTC 2017-02-15 17:46:14
Tagged date : UTC 2017-02-15 17:53:21
Audio #4
ID : 4
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 124 Kbps
Maximum bit rate : 212 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Frame rate : 46.875 fps (1024 spf)
Compression mode : Lossy
Stream size : 102 MiB (2%)
Language : Spanish
Default : No
Alternate group : 1
Encoded date : UTC 2017-02-15 17:53:22
Tagged date : UTC 2017-02-15 18:00:34
Audio #5
ID : 5
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 123 Kbps
Maximum bit rate : 210 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Frame rate : 46.875 fps (1024 spf)
Compression mode : Lossy
Stream size : 101 MiB (2%)
Language : English
Default : No
Alternate group : 1
Encoded date : UTC 2017-02-15 18:00:35
Tagged date : UTC 2017-02-15 18:07:49
tagc : public.accessibility.describes-video
Text #1
ID : 7
Format : Timed Text
Muxing mode : sbtl
Codec ID : tx3g
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 2 bps
Stream size : 1.47 KiB (0%)
Language : French
Default : Yes
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:35
Tagged date : UTC 2017-02-15 19:12:35
Text #2
ID : 8
Format : Timed Text
Muxing mode : sbtl
Codec ID : tx3g
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 86 bps
Stream size : 72.3 KiB (0%)
Language : French
Default : No
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:36
Tagged date : UTC 2017-02-15 19:12:40
Forced Alternative : 7
Text #3
ID : 9
Format : Timed Text
Muxing mode : sbtl
Codec ID : tx3g
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 0 bps
Stream size : 177 Bytes (0%)
Language : Spanish
Default : No
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:41
Tagged date : UTC 2017-02-15 19:12:41
Text #4
ID : 10
Format : Timed Text
Muxing mode : sbtl
Codec ID : tx3g
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 82 bps
Stream size : 68.9 KiB (0%)
Language : Spanish
Default : No
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:41
Tagged date : UTC 2017-02-15 19:12:45
Forced Alternative : 9
Text #5
ID : 11
Format : Timed Text
Muxing mode : sbtl
Codec ID : tx3g
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 81 bps
Stream size : 68.0 KiB (0%)
Language : English
Default : No
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:46
Tagged date : UTC 2017-02-15 19:12:50
Text #6
ID : 12
Format : Timed Text
Muxing mode : sbtl
Codec ID : tx3g
Duration : 1h 54mn
Bit rate mode : Variable
Bit rate : 82 bps
Stream size : 68.6 KiB (0%)
Language : Portuguese
Default : No
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:51
Tagged date : UTC 2017-02-15 19:12:54
Text #7
ID : 13-CC1
Format : EIA-608
Muxing mode : Final Cut
Codec ID : c608
Duration : 1h 54mn
Bit rate mode : Constant
Stream size : 0.00 Byte (0%)
Language : English
Default : No
Forced : No
Alternate group : 2
Encoded date : UTC 2017-02-15 19:12:55
Tagged date : UTC 2017-02-15 19:12:59
CaptionServiceName : CC1
Menu
ID : 14
Codec ID : text
Duration : 1h 55mn
Encoded date : UTC 2017-02-15 19:13:00
Tagged date : UTC 2017-02-15 19:13:00
Menu For : 1
00:00:00.000 : Prologue
00:04:34.000 : The Good Doctor
00:10:17.000 : Medicine And Mania
00:18:32.000 : Kamar-Taj
00:24:37.000 : Open Your Eye
00:31:40.000 : The Mystic Arts
00:38:33.000 : Surrender
00:43:16.000 : Infinite Dangers
00:48:24.000 : Eye Of Agamotto
00:55:34.000 : Sanctum Siege
01:05:04.000 : Astral Battle
01:12:38.000 : Manhattan Mirror Dimension
01:22:14.000 : It’s Not About You
01:28:28.000 : Defending Hong Kong
01:35:01.000 : The Dark Dimension
01:45:06.000 : End Credits
Bit rate mode : VBR