[mythtv-users] Secrets for low powered front ends ?

Patrick Ouellette pat at flying-gecko.net
Wed Oct 12 21:01:27 UTC 2011

On Wed, Oct 12, 2011 at 04:21:07PM -0400, Raymond Wagner wrote:
> > Please tell me *what* codec support I need *right now* that is not handled
> > by VPDAU other than  flash (which I don't watch on my television - I'm a member
> > of the "flash is crap" club).
> If Google is to be trusted, WebM and VP8 may become popular for web 
> video, stuff like MythNetvision is designed to handle.  The bigger issue 
> is all the various options that codecs support.  VDPAU supports H264 
> High, Level 4.1.  If the video uses too many reference frames, you need 
> to apply a work-around, forcing the decoder to allocate more of the 
> GPU's memory for macroblock storage.  There are certain reference frame 
> structures that are not supported.  There are certain macroblock sizes 
> that are not supported.  As far as hardware decoders go, VDPAU is 
> actually fairly permissive as far as these funky options go.  The PS3 is 
> far more limiting.
> MPEG2 and VC-1 each have their own wide range of options of which a 
> hardware decoder can only support a certain subset.  While you will 
> generally be fairly safe in these regards to broadcast TV and Bluray, 
> you may not be so lucky with things like video cameras, and you 
> especially have to be careful if encoding your own material.

"If Google is to be trusted..." google+ will bury Facebook too.  I'm not
interested in "might be" I'm interested in "is available and in main stream
use now" or "is available and use is increasing rapidly."

All the options codecs support are an issue for software and hardware. Someone
decides what options will be supported and codes for them.  the only difference
is once the firmware for the hardware decoder is finalized, it can not be
easily changed. (I would argue the software can't either unless you have the
programming skill to do so - "feature request without a patch")

I'm not interested in web video (in case I haven't made that plain enough)
but in broadcast and optical disc.  Hence I don't see a need for wasted
processing power in this particular case (even if the cost differential is
only $20-$50 up front).

> > If you follow the logic train of "I need to future proof the system I buy" you
> > will never buy anything.
> Futureproofing is done by having a decent amount of CPU power.  Hardware 
> decoding is great.  It lets the CPU idle in low power mode, while 
> efficiently handling all the decoding tasks.  Hardware decoding is 
> inherently limiting, and can only do what the chip was initially 
> designed to do.  CPU decoding can do whatever the software is capable of 
> so long as there is sufficient CPU.  The software can be upgraded for 
> free with an FFMPEG sync, while replacement hardware needs to be purchased.

"So long as there is sufficient CPU" - my argument is chances are relatively 
good the CPU requirements of the new codec will exceed the hardware currently
available *right now* at this price level.  When the new codec is released and
mainstream, prices will have decreased and performance will have increased.

> > Data corruption is a red-herring argument, it can and will "adversely affect"
> > any system.
> Data corruption will happen, and I'm not talking about bitrot, but blips 
> in transmission or reception of TV.  Hardware decoders will not be as 
> forgiving as software decoders.  If FFMPEG hits some garbage data in a 
> recording, it will just skip over it and continue.  If VDPAU hits that 
> same garbage data, it may crash the player, dropping you back to the menu.

I've seen FFMPEG crash on good data and on bad data that hardware decoders
just breezed through.  I've also seen the reverse. The only advantage software
decoding offers *right now* is the ability to patch it to deal with such 
situations.  I happen to know a 1.8GHz processor can software decode at least
720p video, and some 1080i MPEG2.  For my use, I know I'm covered with the
lower processing power.  I expect the system to last 2 years as a front end.
I haven't seen the hardware requirements for MythTV significantly change
since before the introduction of VDPAU and the abandonment of XvMC. 


Patrick Ouellette                 pat at flying-gecko.net
ne4po (at) arrl (dot) net         Amateur Radio: NE4PO 

What kind of change have you been in the world today?

More information about the mythtv-users mailing list