Serviio

Excuse me - I'm a newbie.

I understand, that the standard profile for Sony BDP's, enables rendering of subtitles from separate *.srt files with matroska movies, by spoofing mkv conainers as avi's.

- <!-- set mkv to divx mime-type to allow subtitle and multiple audio track support for European and Canadian players
-->
<MediaFormatProfile mime-type="video/divx">MATROSKA</MediaFormatProfile>

Can the same thing be done with *.mp4 files with h264 video and aac or ac3 audio?

What you understood there in your first sentence isn't correct unfortunately. They're only adjusted to present as DivX (not AVI) because it refers to DivX HD which is H.264 in MKV (which the player officially supports). The subtitles must be integrated into the MKV for the player to decode them. No SRT support I'm afraid.