I’ve noticed an issue thats crept into one of the more recent versions (sorry, I don’t know exactly which one).
Any MKV container that contains subtitles, at least in my case, seem to gain a ‘mystery’ subtitle track selection after downloading to the device.
I have uploaded two images, when playing the exact same file, showing what the subtitles viewer shows when streaming from my NAS and when playing the saved file directly from the device. You can see that some additional subtitle track ‘English’ has appeared when playing the file saved to the device.
This wouldn’t necessarily be a problem, but it seems as if this ‘mystery’ track is very prone to going out of sync. It is also ALWAYS selected by default over the ‘proper’ embedded track. I have noticed that it doesn’t always go out of sync, normally if I start the file from the beginning then I won’t notice the difference, but I’m fairly certain that any file resumed will go out of sync with this ‘mystery’ subtitle track selected. Any file where I have selected the proper embedded track, and then resumed later works as expected/perfectly due to it remembering the subtitle selection.
This isn’t just limited to a particular file, it appears to be anything that contains a single embedded subtitle file. For a file that contains multiple subtitle tracks, no additional tracks seem to be added - e.g. if you have ‘Track 0’ and ‘forced’, no mystery ‘english’ track will appear. But if you only have ‘track 0’, then a mystery ‘english’ track does appear.
I have checked the file that is saved to the device, and no additional tracks seem to be located in the same directory or added to the container - so where is this track coming from and why? If it isn’t added during streaming, why is it appearing on local playback?
Happy to do some more testing / provide more examples if required. I haven’t tried to download files via a different method yet for example. Currently tested on an iPhone running iOS 10 and an iPad on iOS 9. Have plenty of other devices to test on (including iOS 11 soon) if required too.
For reference, here is an example of the files media info from the NAS:
Video
ID : 2
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 51 min
Bit rate : 4 809 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (23976/1000) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.097
Stream size : 1.72 GiB (93%)
Language : English
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Audio
ID : 3
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 51 min
Bit rate mode : Constant
Bit rate : 384 kb/s
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)
Compression mode : Lossy
Stream size : 141 MiB (7%)
Language : English
Default : Yes
Forced : No
Text
ID : 1
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Duration : 51 min
Bit rate : 56 b/s
Count of elements : 798
Stream size : 21.1 KiB (0%)
Language : English
Default : No
Forced : No
