Converting EIA-608 to ASS can have multiple \pos tags

[SuperrSonic]

Summary of the bug:

As described here: ​https://github.com/libass/libass/issues/738
libass rendering doesn't allow more than 1 \pos per line/event.

At the end I include a command line tool that can split the \N on each line to a new dialogue event line, this allows the extra \pos tags to be used, producing an accurate look to the TV's CC decoder.

I could try modifying ffmpeg but I wanted to find out if there's a better way to fix this, or a reason why this shouldn't be done.

The code here seems to be what adds the \N it's always followed by a \pos,
so replacing this code to make it into a new dialogue event should be enough to fix it. How to do that, I am still not sure.
​https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/ccaption_dec.c#L601

How to reproduce:

% ffmpeg -f lavfi -i movie=video.m2v[out0+subcc] -map 0:s -c:s ass video_cc.ass

ffmpeg version N-113881-gf7545e90df-20240301

I've been ripping a lot of my collection to contain these captions, but the tools I've used, like makemkv remove the original caption data, so I don't have any samples right now.

[Marth64]

There is a patch up for this already in the review phase
ffmpeg's new DVD demuxer retains the CC data