[mythtv-users] Recent "pixelation" or "glitches" in recordings (HDHR related?)

[Mike Perkins]

On 23/04/13 20:23, Joseph Fry wrote:
>> I am not sure if the problem I'm seeing is related to the thread started
>>> by Gary Buhrmaster (HDHR glitches and MythTV) so I apologize in advance of
>>> possibly splitting a previous thread.  I have two three HDHR devices (an
>>> older, white case dual OTA tuner, a newer black case OTA tuner, and the
>>> HDHR Prime with cable card).  Within the past four weeks I've been seeing
>>> glitches (some call it pixelation) in the playback of recordings.  I first
>>> attributed it to the possibility that my antenna got rotated by some of the
>>> high winds we've had (I've not checked my signal quality yet).  However,
>>> I've since noticed the same glitches occurring on my HDHR Prime on several
>>> different channels.  Since this is coming over cable, I'd not expect this
>>> type of signal (rarely had it before), so I now suspect something more
>>> sinister within either changes to MythTV or problems with the firmware in
>>> the HDHRs.
>>>
>>> I've upgraded the firmware in all three devices to the March 28, 2013
>>> version with no change.  I'm currently running:
>>>
>>> MythTV Version : v0.27-pre2-760-g575f7d9
>>> MythTV Branch : master
>>> Network Protocol : 77
>>> Library API : 0.27.20130301-1
>>> QT Version : 4.8.1
>>> Options compiled in:
>>>   linux profile use_hidesyms using_alsa using_oss using_pulse
>>> using_pulseoutput using_backend using_bindings_perl using_bindings_python
>>> using_bindings_php using_dvb using_firewire using_frontend using_hdhomerun
>>> using_ceton using_hdpvr using_ivtv using_joystick_menu using_libcec
>>> using_libcrypto using_libdns_sd using_libfftw3 using_libxml2 using_libudf
>>> using_lirc using_mheg using_opengl using_opengl_video using_qtwebkit
>>> using_qtscript using_qtdbus using_v4l2 using_x11 using_xrandr using_xv
>>> using_bindings_perl using_bindings_python using_bindings_php
>>> using_mythtranscode using_opengl using_vdpau using_ffmpeg_threads
>>> using_mheg using_libxml2 using_libudf
>>>
>>> Are others running from Git Master seeing these problems?  Is it just
>>> with the HDHR tuners?
>>>
>>> I do have an internal DVB tuner that I may re-install into MythTV this
>>> weekend to see if these issues disappear.
>>>
>>> Regards,
>>>
>>> -- Ken E
>>>
>>> _______________________________________________
>>> mythtv-users mailing list
>>> mythtv-users at mythtv.org
>>> http://www.mythtv.org/mailman/listinfo/mythtv-users
>>>
>>>
>> I had similar issues with my HDHR Prime in the past (for a few weeks)
>> until I sorted it out.
>>
>> Backend Details
>> Quad-core 8GB ram
>> MythTV 0.26+fixes
>> MythTV storage is NFS mounted from my NAS (5TB storage)
>> Backend set to keep 50GB free
>>
>> I ran my backend disk space almost completely full (just the 50GB buffer),
>> and just allowed MythTV to delete watched content when it needed space.
>> After doing this for awhile I started to notice the pixelation issue on my
>> HDHR Prime. Nothing had changed, so I decided to manually delete all my
>> watched recordings (I don't recall why I decided to try that), and freed up
>> 1+TB on my storage. Since I did that, I've not had the pixelation issue
>> again.
>>
>> I'm not sure if Comcast was just having some issues (the recordings that
>> had pixelation spanned recording dates of a few weeks, so doubtful), or if
>> having an almost full drive was causing issues (50GB isn't that much free
>> space when recording 3 HD broadcasts).
>>
>
> There is no reason that space alone would cause pixelation... however
> running at the limits of your disk space may tigger other issues,
> especially fragmentation.  Additionally, if your disk is mostly empty, it's
> unlikely that two simultaneous recordings would be located too far from
> each other on the disk; whereas when the disk is nearly full you may be
> recording to opposite extremes on disk which could trigger a lot of long
> seek times.
>
> Truely, disk space restraints causing pixelation seems really unlikely,.
> even if heavily fragmented and with lots of seeking, unless you have other
> tasks that are generating a lot of disk IO on top of everything.
>
The issue is not the disk space, it's the fact that myth is having to delete 
files every so often while the recording is being written. Bear in mind that 
most video files are /big/, deleting them could cause some delays to the writes.

-- 

Mike Perkins