First let me say that while both video and audio handling in gstreamer got generally improved I recently came across a clip (video in h264 and dual audio FLAC and mp3 in matroska + karaoke using styled ASS subs) that fails misserably pretty everywhere. Totem plays the audio fine, but the video gets pretty quickly out of sync, in gst-launch the video even eventually stops altogether. Gxine does not support styled subs, but other than that it plays it pretty well, though it picks wrong audio track. Mplayer plays it well, but the subtitles are totally out of sync. And that's probably the biggest woe of recent mplayer builds (where recent spans even to some time before Fedora 10 GA) - slightly more complex styled (ASS) subs are frequently out of sync or not displayed at all (usually when there are more subtitles at once).
So I was looking for a workaround using different video player, but... VLC a xine-lib don't support styled subtitles and for gstreamer there is a bug filled, with experimental plugin attached (using libass). So I've created packages for libass (it's built-in in mplayer, but I needed a standalone library) and for the gstreamer plugin (called assrender) and installed it. Yep, totem does not know about the new plugin for subtitles rendering, but after some googling and trying I sort-of learned how to make gst-launcher use it.
And well, though gst-launcher is good for debugging it's not good for playback, so I wanted to make a simple one-purpose media player using gstreamer and ruby (just for the fun of it :) But it seems, ruby bindings for gstreamer are not exactly in a state that makes it possible at the moment...
The assrender plugin, though highly experimental and not official, works pretty well and even support using fonts that are attached in matroska files (that's a really useful and pretty widely used), but because it supports only RGB colorspace output there are two colorspace conversions needed (YUV to RGB and back) which consumes cpu cycles and on my not so hi-end laptop it makes HD (1280p) videos, that are just about what my CPU is capable of, to fail miserably. So dear lazy web, if you want not-so-hard to do coding for gstreamer, you can help out with bringing libass support there. It would remove the last obstacle which prevents me from using gstreamer for everything ;-)
But at the same time, I am a bit concerned about mplayer as well - because on the same hardware, since Fedora Core 6 it's playback capabilities are getting steadilly worse. Not that it cannot play videos, but mplayer tends to fail resuming of paused video, then there's the issue with subtitles and lastly I've experienced a very weird bug (and workarounded it for my own purposes) - there's one assertion in ffmpeg code that prevents playing of certain matroska videos in mplayer.
Basically someone obviously expected that if you have chapters in a movie, than they will be strictly chronological, meaning next chapter (in list) won't start before current one. In matroska this is not always true and the failed assertion makes mplayer crash... For those who are interested, it's in libavformat/utils.c in compute_chapters_end () somewhere around line 1950 or 1960... It's this simple line:
assert(s->chapters[i]->start <= s->chapters[i+1]->start);
I'm still in doubts whether I should fill a bug or not about it... In my opinion there should be just if conditional, assert seems to me like an overkill, especially given that not aborting the code here (if the assertion fails) does not make mplayer doing things it is not expected to do.