Issues with IDX/SUB Subtitles Embedded in MP4/MOV Containers


Let me start by thanking the WDTV engineers for supporting this feature.  As far as I know, none of the competition does and it is probably the number one reason I am keeping my WDTV Live as my principal media player.

Unfortunately, while embedded IDX/SUB subtitles do work alright for some shows, with others there are serious problems.

First, the coded length of subtitles appears to be completely ignored for almost all subtitles.  Rather than stopping when it is supposed to, the subtitle just keeps displaying for an indefinite period, often only clearing when the next subtitle begins.

Second, for some shows–in particular Japanese anime, it appears–90% or more of subtitles just don’t display at all. Every once in a while a subtitle shows, but the vast majority appears just to be ignored.  

Third, and least seriously, but still annoying, the language of subtitles seems to be frequently misidentified.  For example, English subtitles are routinely listed as Castilian (!?).

All of these problems appear on many or all of my DVD collection (stored in mp4 format on a ReadyNAS server).  All of these files exhibit none of these problems when played on a computer using, for example, VLC.


Any particular reason you went with the MP4 container?


There really are only two modern, widely-used non-crippled container formats that accommodate both current codecs (like h264 and AAC) and an appropriate set of meta-data: MP4 and MKV.  MKV has some advantages but MP4 has much better hardware support (including various iDevices, PS3s, XBox 360s, etc.) and somewhat better software support (including iTunes), so that is the one I chose three years ago when I transferred my DVD collection to my ReadyNAS.

Are you suggesting that MKV would work better with the WDTV Live?  It is possible, I believe, to convert mp4 to mkv without reencoding and while preserving meta-data.  But even so, it would be a massive task for thousands of files and terabytes of data and would forfeit a great deal of compatibility with other device.


Well, at least you should be able to determine if your idx/sub problems stem from the container you used of if it’s the subs themselves. I’ve had some Vobsubs with more than one stream that had dropouts during playback. Only remedy was to reduce them to one language.


I did try removing the other subtitle tracks, but that did not affect the dropouts in the remaining subtitle track.  I will try remuxing a test file to MKV to see if that changes anything, but even if it does that would just indicate that there is a bug in the WDTV Live’s MP4 parsing.

If any WDTV engineers could investigate the problems recounted in my first post, it would be much appreciated.  I’d be happy to offer sample files which exhibit the problem.