[linux-dvb] DVB API update

Georg Acher acher at in.tum.de
Tue Sep 18 12:02:21 CEST 2007


On Tue, Sep 18, 2007 at 02:50:09AM +0400, Manu Abraham 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

I have h.264 playback running on a really slow Geode with 300MHz. For a
15Mbit/s stream, the TS path from the DMA buffers into user space needs
about 5% CPU with traditional memcpy(). I wouldn't call that optimization
worthy... What really counts is the postprocessing in user space (remuxing,
repacking, etc.). The API may support this with single PIDs per
read filedescriptor, but I don't think it makes a difference where the data
is actually filtered...

-- 
         Georg Acher, acher at in.tum.de
         http://www.lrr.in.tum.de/~acher
         "Oh no, not again !" The bowl of petunias



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