Ripping EIA-608 out of h264 mp4 issues?

[RedPenguin]

I am trying to convert files like the following:

https://live-content.xumo.com/1836/content/XM0DL3PSX65VEB/21623372/master.m3u8

It appears to be similar to other h264 videos I’ve gotten that have EIA-608 CC.

Yet normally I don't get any errors at all in CCExtractor but this video and others from the site give me:

"Warning: Probably loss of CC data, unsaved buffer being rewritten, trailing end might get lost"

I tried looking up this error but I oddly only get results from the actual CCExtractor, not anyone asking about the error.

I also tried:

ffmpeg -f lavfi -i movie=test.mp4[out+subcc]  -map 0:1  output.srt

which worked great other than saying

"[Parsed_movie_0 @ 0000020fc3a0e080] EOF timestamp not reliable" but Google results say normally that can be ignored.

Yet if I try and tell ffmpeg to encode using the produced srt, ffmpeg randomly stops and exits after a few seconds.

[RedPenguin]

Actually I think I figured it out.

I noticed if you look at the ffmpeg produced SRT you see tags like <font> and similar.

I thought maybe that's throwing things off as other mp4's from CCExtractor and just SRTs I got offline never had tags like that.

So I told ffmpeg just make a "VTT" out of the subtitles and then right after it was happy to encode me a new file with the subtitles.