[linux-dvb] DVB API update

Manu Abraham abraham.manu at gmail.com
Tue Sep 18 13:57:20 CEST 2007


Janne Grunau wrote:
> 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.


The case of a 20Mbps stream getting recorded is not a great thing. when
you have a TS with symbol rate 27.5Msps, (capturing the complete TS) the
normal TS itself is about 27Mbps (in a very crude rounded off case)

So, the situation that you have isn't larger than a situation having a
normal single DVB-S card.




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