[mythtv-users] Prebuffering pause on Frontend playing back BBC HD

Mike Choy mike at acaciaclose.co.uk
Tue Jan 2 16:10:49 UTC 2007

Andrew Lyon wrote:
> On 1/1/07, Chris Dos <chris at chrisdos.com> wrote:
>> Mike Choy wrote:
>>> I've just built a amd 4200 X2 with 1GIG on asrock motherboard using suse
>>> 10.2 and packman rpms. The asrock has an on board Nvidia gforce 6100
>>> GPU, but uses shared memory. On playing BBC HD in the UK (h.264 based
>>> stream) I'm getting stutter and NVP prebuffering pause on running
>>> mythfrontend. Have tried all permutations of XV, standard  mpeg decoders
>>> , deinterlacing etc
>>> I was under the impression also that playback should not be a problem.
>> I think that this shouldn't be a problem for mpeg2 playback.  But from what I
>> understand, the decoders for h.264 in ffmpeg aren't quite up to snuff for speed.
>>  So your system might not be powerful to playback h.264.  Can you play back
>> mpeg2 without prebuffering pauses?
>>> I have recorded the stream and on playback it still stutters. Top shows
>>> 50.1% CPU utilization.
>> You might want to hit the "1" key during top to show each individual core's
>> usage.  It's probably one thread that is maxing out one of the cores.
>>> As this is a brand new rig  here is what I'm doing to try and trouble
>>> shoot this. (any further hints and data points also welcome)
>> Yea, I'm kinda in the same boat as you are.  Are you using SVN?  I don't know if
>> the packman rpms are MythTV RPMS or not.  I'm running stock 2.6.19 kernel that I
>> rolled from from kernel.org, Debian Sid, MythTV SVN, and the latest nvidia driver.
>>> 1. Have downloaded 720p and 1080p h.261 sample movies from  digital
>>> digest (pirates of the Caribbean)
>>> http://www.digital-digest.com/movies/pirates_of_the_caribbean2_h264_1080p_trailer.html
>>>     in Mplayer  top is showing 46%
>>> 2. Playing the above file under the internal video player is showing 46
>>> to 49%.
>>> 3. Playing the recorded stream in Mplayer seems to be a bit better but
>>> slow frame rate, but It is showing a lot of video corruption.  Also i'm
>>> getting the error message "too many video packets in the buffer"
>>> constantly, and Top shows 65% CPU.
>>> 4. I saw a post where the stutter NVP prebuffer pause was a result of
>>> poor Aeriel, and I think this might be an issue as I suspect that HD is
>>> more critical to the quality of the downlink. ( no problems with SD TV
>>> payback on my system). Will try and use a better downlead as soon as I
>>> can rig it up.
>>> 5. Has anyone got a BBC HD recording that is clean that I can download
>>> to test the system with?
>> Because you are trying to playback h.264, I don't think there are any hardware
>> accelerators that you can buy at this point for linux.  I think you're going to
>> have to do everything in software.  Just like that I'm trying to do.  I can get
>> away with using XvMC for now, but it's not my ideal solution, and it's not a
>> solution that will work for you.
>> I wonder if the developers can start threading the playback app somehow so it
>> can start using more than one core.  I don't want to even imagine how difficult
>> that might be to pull off.
>>         Chris
>> _______________________________________________
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>> mythtv-users at mythtv.org
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> The problem is that the BBC HD is encoded with MBAFF H264, currently
> ffmpeg cannot decode it in realtime even with a very fast cpu.
> Normal H264 is ok, it is MBAFF that causes the problem, it is a type
> of interlacing that makes decoding very cpu intensive, support for it
> was only recently added to ffmpeg so perhaps it may be optimised and
> improve in the future.
> Alan Nisota wrote a patch that allowed mythtv to use CoreAVC Codec to
> decode H264, that is the only codec that can decode MBAFF in realtime,
> but it is a windows product. His patch works wtih CoreAVC 1.1 which
> does not support MBAFF, I had a email from him this morning, he might
> try to get his patch working with CoreAVC 1.2, I believe that would
> allow realtime playback of BBC HD.
> For the moment the best you can do is record and transcode anything
> you want to watch on BBC HD.
> Andy
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Thanks Andy/Chris

During playback of recorded stream (Deinterlace off, standard mpeg
decoder) when I hit the "1" key in top it does indeed show CPU 1 running
at 98% to 100% CPU, CPU 0 at 2%. So it does look like the poor little
CPU is going at it hammer and tongs :-) quite interesting to see the
load swith between cpu 1 and cpu 0 every now and then.

As expected XvMC, libmpeg make s no difference.

I assume that Myth uses ffmpeg libavcodec for play back, so we will have
to wait for the ffmpeg crew to do their stuff.
I also assume that once we have an optimized ffmepg Mplayer will just
work as would mythtv.

Does Core AVC 1.2 work with mplayer?

I am still interested in what others are getting in terms of CPU hit
 relative to their rigs, ie how far do we need to go b4 this thing will
work. Sounds like there is no hardware available to decode BBC HD unless
Nvidia /ATI give us linux driver support for their h.264 drivers.

Mike C

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