The VideoLAN Forums

Hi everyone. I'm having an interesting problem (which I believe to be a software bug), regarding subtitles in a MKV package.
It doesn't seem to matter what codec is used- as long as there's ssa subtitles. But for purposes for testing, I played an MKV file with SSA subtitles, H264- MPEG4 AVC (Part 10) (avc 1) Video, with a Planar 4:2:0 YUV 10-bit LE decoded format, and MP4a audio.

I played this file on 2 computers. A macbook from 2007 running Mac OS Lion with a Intel Core 2 Duo 2.16ghz Processor, and a Intel gma950 graphics card, 3gb of RAM. There was no lost frames.
The second computer: Homebrew PC running Windows 8 Pro with a 2.6thz Quad Core Athlon II x4 620, Radeon HD6570 graphics card, and 8gb of RAM. 32 frames lost in 4 seconds. The audio played perfectly. If I turn off subtitles, there's no problem.

I've NEVER had an issue playing any sort of video file on my homebrew PC- and MPC plays all of my files just fine. There's one issue. I don't like MPC. This is an issue that I actually noticed starting around 2.0.3 I think? And it's progressively gotten worse. I've tried the nightly build 2.0.6- as well as 2.0.5- and reinstalling, removing the cache and preferences, no dice.

One thing strange that I DID notice- was on one file I played where the video and audio froze completely, the time elapsed and remaining had a blueish background. Hope that helps.

I've given all of the details that I can think of right now. I hope this is of use- and if it is a bug, that you can find it and squash it.
Thanks!

EDIT: I've tried enabling GPU decoding, skipping the H264 loop, and turning off post-processing. Oh, and the issue gets worse the longer the file is. (~20 minutes lag, ~40 minutes+ won't play)

I'm not sure to get your issue... when you play mkvs with ssa vlc drops frames? Did you try another video output?

Keep in mind that every time you change preferences you have to restart vlc.

Thanks for your reply. Yes, VLC drops frames when I play MKV's with SSA subtitles. And I have restarted VLC every time I've changed the preferences. The video output that I get the least number of dropped frames is the Windows GDI output (which looks hideous), and the default output (not sure what that is) gets the most dropped frames. Direct3d and OpenGL are bearable, but the picture isn't as sharp- and there's still dropped frames, which doesn't make the drop in quality worth it to me.

Well it's very strange then... when GDI performs better than opengl and direct3D, it's usually time to update your GPU drivers.

Hmm... I just got a new graphics card, with the latest drivers from AMD. I've even tried overclocking the card- nada. I suppose reinstalling the drivers might be the way to go in this case; it's worth a shot at the very least.

And the driver version I am running (which is the latest for my card, at least) is 9.012-121219a-152192C-ATI. I'm not sure if there might be a specific issue with that package or not. I suppose I can give the beta drivers a shot, too.

I've also installed Linux on a separate partition (which I've been meaning to do for awhile), and I'll try playing the files with the Linux port of VLC to see if it might be the graphics card itself that's causing the issue (and/or drivers).

Quick update: driver reinstall and update to the beta drivers didn't do anything. *HOWEVER*- I just got an update request, so of course, I downloaded it- only to have the file discarded because of an invalid CRC32 signature. This happened twice, and the download mirror had the .videolan.org domain, so this further makes me think that it maybe a software issue. Though I understand that CRC32 signatures don't really have anything to do with my problem.

Here's what I don't get. MP4 at 6 mb/s output (burned-in subtitles), no problem. Not a single dropped frame in 30 minutes. MKV at 2.54 mb/s output (with SSA subtitles)? 131 dropped frames in just a few minutes. You would think that a more graphically intense file would cause MORE issues, rather than less. So I guess that rules out the graphics card as the issue.

It is more CPU intensive to render subtitles, scale and blend them than just playing hard subbed so it is not that part that is surprising. Especially since SSA subtitles feature many possibilities which can cost a lot of computation.

Still... the fact that GDI is more efficient that Direct3D shows system problem, it may be related to win8 since it introduced a lot of changes and vlc is still being developped for it. (so are drivers)

I never had any problems with ssa subtitles on a win7. If it was with only one file I could blame the demux or the core since VLC struggle with high framerate videos but for now, I'm interested in the linux test on the same computer.