MPEG2 playback choppy

[theophile]

Hi all. I've spent the past couple days getting XBMC working to my liking and boy do I like it! I'm coming from MythTV which I still use for DVR functions. I have XBMC set up properly as a frontned to MythTV but sadly, playback of high definition recordings is unusable. The video is very choppy, the audio begins to de-sync and stutter and it's unwatchable at this point.

Since I can playback in MythTV fine, I know my hardware's okay. I'm running on a P4 2.4 and an nVidia FX 5500 with latest binary drivers.

Are there tips/tricks for playback of high definition content? Thanks!! :nerd:

[dteirney]

Are you playing the mpeg2 material through the myth:// protocol?

I'm using the myth:// protocol and have issues with audio sync when skipping (sometime just from starting). Seems to be related to huge CPU requirements to decode 1080i h264 though.

What version of XBMC are you running?

Also, you could try playing the recordings directly to see if there is any difference. To do this simply add a new Video source that points to the mythtv recordings directory. I tried this with some 1080i content and still got pretty average playback rates (~19FPS). That was with H264 though.

My old analog content that was recorded with a PVR-500 as MPEG-2 used to playback fine in XBMC on the Original XBox. Haven't got around to importing the recorded shows from the DB into the new HTPC to test them though.

If you have Upscaling of content to HD turned on in the XBMC Video Player settings then turn that off. That made all my ripped SD content choppy (albeit MPEG-4).

[dteirney]

Also try, http://xbmc.org/wiki/?title=MythTV#Audio_Plays_Out_of_Sync

[theophile]

The advancedsettings.xml trick helped a lot. Now the audio and video don't drift out of sync, but the video playback is still not smooth. It's like the video plays too slow for a moment then speeds up to get back in sync, then drags a bit and speeds up again. This cycle repeats every second or two. The audio (AC3 passthrough) does play smoothly, however.

What's the best renderer to use with HD content? I guess I'll have to do trial and error.

[dteirney]

I only get 19 FPS with 1080i h264. Playback is just watchable but I'm still having issues with the audio getting out of sync when skipping. CPU cores are running 100% and ~70%. 720p h264 playback seems to be much better but still has the occasional video and/or audio stutter.

Until there is something put into ffmpeg or XBMC as a patch to ffmpeg that helps alleviate the amount of CPU used to decode full HD (or better utilizes both cores), smooth playback is still a ways off for me. I'm running an AMD / ATI system and most people seem to think that an Intel Core 2 Duo chip of at least 3Ghz is the way to go. I was pretty sure my dual core 3.0 Ghz AMD would be fine but apparently not. Going to try overclocking once I've got a better CPU fan installed.

I'm hoping the next ATI Catalyst driver release will improve OpenGL performance because I suspect that is causing some issues as well.

[dteirney]

I've tried both the Basic and Advanced Shaders for the Renderer. Currently I'm running Auto Detect. Not sure which one that chooses but I think using the Basic Shaders was ever so slightly less choppy. No discernable difference with either FPS or dropped frames though so not really sure.

Oh, and perhaps check that what you are seeing is not tearing. I had that problem initially and thought it was choppy playback. Using ATI drivers you have to turn on VSync to always on in the Catalyst driver and then set to "Driver Detect" in XBMC. Much more information in http://xbmc.org/forum/showthread.php?p=261647. Not sure if that thread covers any of the other major video chipsets or just focuses on ATI.