[linux-dvb] DVB API update

Rudy Zijlstra rudy at grumpydevil.homelinux.org
Tue Sep 18 13:45:29 CEST 2007


Manu Abraham wrote:
> Georg Acher wrote:
>   
>> 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...
>>
>>     
>
> You are looking at a single DVB-S2 demod. There are dual S2 demods in a
> single chip config.
> Consider that with multiple adapters, even if you ignore post processing.
>
> If you have a larger number of adapters and you have to do post
> processing, there is quite a large unnecessary overhead, even if you
> don't do software decoding.
>
> Are there only a very few people having multiple DVB adapters in a PC ?
> (I guess people having dual and quad demods (single demod/chip) on an
> adapter and having multiple adapters can be quite a small fraction)
>   
2 systems with each 4 DVB tuners. test system has 3 DVB-S + 1 DVB-C. 
operational its 4x DVB-S

The DVB-C is capturing H.264 though.... and not problems in capturing.

capturing and demux is not the problem. Displaying it (postprocessing) is.

Cheers,

Rudy



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