[mythtv-users] Poor playback performance on Mac mini

[James Linder]

On 11/03/2012, at 7:14 AM, mythtv-users-request at mythtv.org wrote:

> I am currently trying to investigate why my Mac mini frontend will not playback live TV and recordings smoothly for certain channels.
> 
> Some background info:
> 
> Backend
> Dell PowerEdge T110II
> Xeon E31230 3.2 GHz (Quad core +HT) CPU - 4 cores assigned to MythTV backend server
> 1GB RAM 1333MHz DDR3 assigned to MythTV backend server
> Recordings stored on 3 1TB Seagate drives in md RAID5
> Ubuntu 10.04 LTS x64
> MythBackend fixes/0.24 [v0.24.2-19-g02dd6ee] - kindly provided by Mythbuntu repositories
> HDHomeRun HDHR3 as the TV source - UK Freeview, so SD quality
> 
> Primary Frontend - TV
> Mac mini (Mid 2010)
> Core 2 Duo 2.4 GHz CPU
> 4GB RAM 1067 MHz DDR3
> NVIDIA GeForce 320M 256MB GPU
> OS X Lion (10.7.3)
> MythFrontend jyavenard/backports/fixes/0.24 [v0.24.2-216-g247c4f1-dirty] - Kindly provided by Jean-Yves Avenard
> 
> Secondary Frontend - Office
> iMac (Mid 2010)
> Core i7 2.93 GHz CPU
> 8GB RAM 1333MHz DDR3
> ATI Radeon HD 5750 1GB GPU
> OS X Lion (10.7.3)
> MythFrontend jyavenard/backports/fixes/0.24 [v0.24.2-216-g247c4f1-dirty]
> 
> My LAN is all gigabit.
> 
> Basically, I am getting poor playback performance on my primary frontend - the Mac mini. When I say poor quality, my best description would be that the picture is jumpy - motion is not 'fluid' and it appears 'jerky'. Slight glitches can be heard in the audio too. At first when I saw this issue, I thought that it was just the GPU was unable to cope. However, This weekend, I have decided to do some investigation into the issue, finally.
> 
> If I record from a BBC channel, I get normal playback quality - i.e. the quality is as good as on my iMac
> If I record from an ITV, Channel 4, etc. channel, I get poor playback quality, as described above.
> If I watch live TV from a BBC channel, I get normal playback quality - i.e. the quality is as good as on my iMac
> If I watch live TV from an ITV, Channel 4, etc. channel, I get poor playback quality, as described above.
> I am able to play 1080p video on my primary frontend, with absolutely no quality issues through XBMC.
> I am able to playback recordings from any channel in VLC on my primary frontend, with absolutely no quality issues.
> I have monitored GPU usage on my primary frontend, and my GPU usage is around 15% (IIRC) when playing back recordings from any channel.
> CPU usage is around 50% on my primary frontend when playing back recordings - I'm not sure this is all MythFrontend, but it proves the point that the CPU is not exhausted.
> RAM usage hovers around 2GB mark on my primary frontend.
> Backend server does not appear to be exhausted in any way.
> I have tried all playback profiles on my primary frontend.
> All recordings and live TV plays back fine on my secondary frontend (the iMac), but I rarely find the time to use MythTV on this machine.
> 
> As you have gathered, I'm a little bit stuck now, on what could be causing this issue, and I was wondering if anyone had any ideas how I should proceed with this?
> 
> I'm not sure what the significance of the different behaviour with different channel providers is - the fact that I get good playback quality in other apps on the same frontend and BBC channels (to me) proves that the frontend is 'capable'.
> 
> I really hope someone could help me out with this.

Since the issue has plagued me too some feedback ...
I've not run a frontend on my mini
NVIDIA playback is instantly noticeably better than ATI (I even installed SuSE and ubuntu on my iMac, but heat generation, even throttled to 1G is too much, and did the A/B comparison with various frontends)
You too have the 50Hz vs 60Hz for all US based movies jitter issue.
So native 50Hz video is acceptable on ATI, but 60Hz is very jerky.
If, perchance, you watched 50Hz stuff on BBC and 60Hz stuff on ITV then you could understand.
Mac use SLEEP at full speed not THROTTLING to manage heat.
 
I've found that a smaller display is the only solution. I wait with bated breath to hear anybody's wisdom

James