Stuttering playback of 720p/1080p mkv when enabling subtitles

[skr@icelab.dk]

I have discovered (as many people before me) that enabling subtitles on high resolution MKV's can cause the playback to stutter on some hardware, whereas it plays fine on the same hardware if subtitles are not rendered.

On my hardware the CPU load goes from approx 8% (no subtitles) to 98% (with subtitles).

I don't think that rendering the subtitles can require that much additional computation power, rather I think that when adding subtitles it is for some reason no longer possible to use hardware acceleration.

Is there some knowledgeable person out there who can tell me if I'm right or wrong? And if I'm right maybe even explain why hardware acceleration becomes impossible?

Kind regards,

- Stephan

[lowellriggsiam]

Do you get the same result when you play the same MKV on a different player, it VLC or DIVX Player? If you shrink it using handbreak does it correct it? What method di you use to make this MKV?

[skr@icelab.dk]

MPC-HC: (1) Perfect video at 8% CPU with no subtiles using the "WMR7 (windowed)" renderer. MPC is using the internal MPC Video Codec (but same result with CoreAVC codec). (2) Stuttering but clear video with subtitles using the "WMR7 (renderless)" renderer. CPU at approx 90%.

Graphstudio shows me that an additional filter has been added in relation to the subtitles for (2) above.

VLC: I can hear the sound but no or very bad video. CPU at 30%. subtitles available. Graphstudio cannot connect. I cannot immediately figure out how to configure vlc to achive similar playback as MPC-HC.

DIVX Player: Same as MPC-HC (2). Looks fine, with subtitles, but stuttering playback, high CPU utilization.

I'm shrinking the video now with handbrake, but ETA is approx 3 hours so no results yet.

Mediainfo tells me that the video is "AVC" made by mkvmerge, audio is DTS, and text is UTF-8. It was downloaded from the internet so I don't now the actual origin.

[lowellriggsiam]

Handbreak does a good job, although the wait time is annoying. My PC has a 9600 Phenom w/ 3gigs of ram and a 2400 HT video card running Vista SP2. If I use makemkv to make a blu_ray into an MKV file the raw MKV files can be in excess of 30GB and they play fine in the updated DIVX media player, subs on, or off. My thinking in your case may be that if the video is shrunk it reduce the needed resources and better allow for playback.

[jagabo]

Try different output devices in the media players. Also try different MKV splitters. I can get similar problems with some combinations of filters.

[skr@icelab.dk]

Hi,

Thanks so much for the help. I can now play my movies with subtitles and without stuttering playback. I found that if I used MPC-HC and chose the "WMR9 (renderless)" playback device it worked. I had previously only tried "WMR7 (renderless)". I don't know how I could be so stupid and not just try all of them

Anyways, I made some progress.

BUT I can only get it working in MPC-HC when using the internal subtitle filter (appears as TextPassThru??). If I attempt to use VSFilter (directvobsub) or ffdshow subtitle filter the subtitles appear, but the stuttering becomes very bad again

Why would I want to use the other filters? Well, it will allow me to use other players, and I'm curious as to why only the internal MPC-HC subtitle filter is working well in my setup.

One final question: Is it possible to install the internal MPC-HC subtitle filter as a global filter for other players? I know you can do that with the MPC Video Decoder, but what is the name of the MPC subtitle filter (if such a one exist)? And will it work outside MPC?

Kind regards, and thanks for the input!