I have some proprietary video playback software wich I want to use with subtitles. Unfortunately, it only accept subtitles in weird .m4t format. I am searching for any .m4t subtitles file sample.

All known info:
1. It is SMPTE-compliant TTML-based subtitles, mostly used by Sony.
2. From Android core code:

<AdaptationSet id="3" group="3" contentType="text" mimeType="application/vnd.sony.m4t" codecs="smtt" par="16:9" sar="1:1" lang="en">
<Role schemeIdUri="http://xmlns.sony.net/metadata/mpeg/dash/role/2012" value="forcedSubtitle"/>
<Representation id="3_1" bandwidth="0" width="854" height="480">
<BaseURL>Subtitle43.m4t</BaseURL>

3. Samples were previous available here:
http://hollywood.cs.connect.com/hlspoc/Discovery_SMPTE_TT_Complete_Testsubtitle_Track 5.m4t
http://hollywood.cs.connect.com/hlspoc/Discovery_SMPTE_TT_Complete_Testsubtitle_Track 5.m4t

Both links are now down and not archived anywhere.

4. Google search might suggest to you that .m4t is video format or Sage Mas 200 database, but this is not true in this case.