[linux-dvb] DVB API update

Janne Grunau janne-dvb at grunau.be
Tue Sep 18 02:13:31 CEST 2007


On Tuesday 18 September 2007 01:41:04 Manu Abraham wrote:
> Johannes Stezenbach wrote:
> > On Tue, Sep 18, 2007 at 02:50:09AM +0400, Manu Abraham wrote:
> >> Johannes Stezenbach wrote:
> >>>
> >>> The recording filters are exactly the piece from V4 which has the
> >>> "mmap DMA buffers" zero copy API. But to be honest, I don't think
> >>> it's important on a PC which can copy > 1GByte/s in RAM. More
> >>> interesting would be the ability to have multiple independant
> >>> filtered TS outputs instead of just one dvr device.
> >>
> >> Currently have you tried playing back a High Bit rate H.264 stream
> >> default of a DVB-S2 stream ? I guess not.
> >>
> >> If you have had, you will see my reasons why i am trying to
> >> optimize the overheads.
> >> BTW: it is not RAM that matters here, but CPU horsepower
> >
> > A demux doesn't decode, and what matters is memory bandwidth.
>
> Try running a software decoder alongwith and tell me that that
> decoding doesn't need CPU

right the software decoder needs cpu power.

> and then the options what you can look at 
> is cutting whatever overheads it is.

Wrong, you would start optimizing parts with take significant time. I 
can record 20mbps streams on a machine capable of decoding H264 1080p 
video with more than 99 percent idle. So even if you can optimize 
capturing the stream to taking zero cpu cycles (and you can't) you will  
see at most 1% increase in decoding speed.

While having zero copy demux would be nice, it is neither relevant for 
H264 decoding nor DVB-S2.

DVB-C qam256 8mhz channels have the same bitrate as DVB-S2 transponders 
and work just fine now.

Janne



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