How to fix subtitles that are out of sync with video

[Mam]

MKVToolnix creates a .mkv and ffmpeg can put text-based subtitles in a .mkv container.

Not sure about the ts, I only use mkv.

TS = Transport Stream = a lot of unneeded garbage.
Strip it off, encode to PS (Program Stream), save up to 2/3 space without losing any quality.

So my storage only contains reencoded MKV files, saving a lot of disk space...

Unless you do not want to re-broadcast the video, TS is not needed.

[Cypheros]

TS is a very special format. ffmpeg, tsmuxer and other tools like that often have problems with this kind of files if there are errors in the stream. When receiving Transport Stream via satellite, cable or antenna, reception interference occurs from time to time, especially during bad weather or poor reception paths.

Missing or bad packets often leads to sync problems between audio, video and text streams if you convert them to other container formats.

Personally, I leave the format untouched and don't waste time and expensive electricity on conversion just to save a bit of disk space. Storage space is so cheap these days.

[ErichV]

From what I can tell, ffmpeg can only mux subtitles in to a .ts container that are in bitmap-based and not text-based format. Furthermore, currently it cannot convert text based subtitles into image based and vica versa. Does that sound correct to you?

That makes sense. I don't use ffmpeg, but the *.ts container doesn't support *.srt or any other text-based files.

So I used "Subtitle Edit" to export the corrected .srt (text) file to VobSub (image) format and then muxed that in as above. I prefer the way the subtitles look by adding them back to the .ts stream in text-based form but in that case ffmpeg apparently requires the container to be .mp4. Maybe I would loose some quality if I convert the .ts to .mp4? Is that correct do you know?

The elementary streams remain untouched, so quality wise the output is the same. However, you use a different container and *.ts files store more information than any other container format. Therefore, *.ts files are the most robust ones when it comes to data transmission.

I cannot get a definitive from searching around... for instance exactly what subtitle codecs ffmpeg supports in a transport stream container. Would you know the answer to that or how to find the answer to that?

It's not about ffmpeg, it's more about what the transport stream standard can handle or not. Just google MPEG-2 transport stream specification (ISO/IEC 13818-1) for more information.

MKVToolnix creates a .mkv and ffmpeg can put text-based subtitles in a .mkv container.

Of course it does, because *.mkv files support *.srt files as elementary streams.

Overall, I think your workflow is a good solution. I've never seen such a huge delay to the video stream in any *.ts source file.