You can use ffmpeg (not avconv) to do the trimming/splitting recordings
with subtitle stream.
When you have movies with hard subtitles (picture-based subtitles) you must transcode to a container with the "hard subtitle" as a overlay video over the actual videofile. For instance, dvdsub is a type of picture-based overlay subtitles. With hard subtitles you don't have to export the hard subtitle to a .srt or .ass file as with soft subtitles.
Exampel: Here I have a Matroska file with two dvb_subtitle. Ffmpeg will choose the first stream by default, which is Stream #0:3(nor). You can also choose the other subtitle in ffmpeg with the correct Streamid.
ffmpeg -i Matematikkmysteriet.mkv
Stream #0:0(eng): Video: h264 (High), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 50 fps, 50 tbr, 1k tbn, 100 tbc (default)
Stream #0:1(nor): Audio: mp2, 48000 Hz, stereo, s16p, 256 kb/s (default)
Stream #0:2(nor): Audio: ac3, 48000 Hz, stereo, fltp, 448 kb/s (default)
Stream #0:3(nor): Subtitle: dvb_subtitle (default)
Stream #0:4(nor): Subtitle: dvb_subtitle (default)
The ffmpeg command will be:
ffmpeg -i Matematikkmysteriet.mkv -filter_complex "[0:v][0:s]overlay[v]" -map [v] -map 0:a Matematikk.ts
Everything is well documented in the Ffmpeg wiki here:
https://trac.ffmpeg.org/wiki/HowToBurnSubtitlesIntoVideo
You can also do trimming/splitting recordings with ffmpeg if you know the starttime and the stoptime or the duration.
Look here for ffmpeg exampel:
https://trac.ffmpeg.org/wiki/Seeking
Here is a exampel where I cut the beginning of the recordings with 2 minuts and the duration of the video is 55 minuts
with hard subtitle stream:
ffmpeg -ss 00:02:00 -i Matematikkmysteriet.mkv -filter_complex "[0:v][0:s]overlay[v]" -map [v] -map 0:a -b:v -t 00:55:00 MatematikkCutted.mpg