[rpcameron]

I know that Kodi can decode VBI-encoded CEA-608 Closed Captions. (These are different from teletext streams in DVB broadcasts that are transmitted as a separated media stream; closed captions are encoded in the data stream of the video stream itself, and therefore need to be handled separately/differently.)

However, my problem is that when enabled closed captions/subtitles on my broadcast streams, the text ALWAYS lags behind when it should be displayed. (Meaning a full 3 seconds or so, not just a trivial 500ms or so.) Is this hardware dependent, or just Kodi's fault.

All of my frontends are presently armv7hf, and I've noticed this on both 17.6 and 18a1. I have yet to test this on x86_64, but I am getting ready to migrate my main living room machine to something more powerful, so I'll test that, too.

Have others noticed this problem, or am I an outlier? What does Kodi use for CEA-608/708 decoding? Last time I built it from sources I think I remember seeing references to libzvbi, but I'm not certain. If that is not the library, it is something in-house? (I know ffmpeg's CC parsing is rather rudimentary ...)

[rpcameron]

Quick update: Earlier this morning I ran the test again, and CCs seemed to be appearing properly on the Pi3 frontend. Once I've finished the build of 18.0a1 for x86_64, I'll check again. The quick test this morning was done with a recorded program (as opposed to a live stream), so I'm not sure if that makes a difference.

I'll also check with a comparison with mpv and vlc on x86_64 and omxplayer on RPi.

[rpcameron]

It appears that it must have been a bad/mis-configuration on my part, as the CC decoding in Kodi seems to be matching up with other players, and different platforms (ARMv7, aarch64, x86_64). I must have been not recognizing the change from CCs on scripted programming versus the delayed captions with live broadcasts (such as the news).

However, this does now brings to light a new missing feature: CC positioning. Part of the encoding of closed captions includes style and position information. Other players (such as mpv/vlc) respect the positioning information for closed captions (while mostly ignoring the styling information), but Kodi does not. It merely applies the same positioning and styling as the subtitle settings. In general this isn't a problem, however one of the niceties of allowing closed captions to define their own positioning is that they can be placed towards the top of the screen to prevent obscuring text in the program at the bottom of the screen; or for dialog to be displayed beneath the speaker, aiding in understanding by context.

Are there plans to implement closed caption positioning that overrides default subtitle settings?