[mythtv-users] MythTV vs. Windows Media Center

[Raymond Wagner]

On 2/12/2011 01:27, Reynolds, Brian wrote:
> -----Original Message-----
> From: mythtv-users-bounces at mythtv.org
> [mailto:mythtv-users-bounces at mythtv.org] On Behalf Of Raymond Wagner
> Sent: Friday, February 11, 2011 10:20 PM
> To: Discussion about MythTV
> Subject: Re: [mythtv-users] MythTV vs. Windows Media Center
>
> On 2/11/2011 22:11, Rob Smith wrote:
>> On Fri, Feb 11, 2011 at 6:38 PM, Reynolds, Brian
>> <Brian.Reynolds at fiserv.com>   wrote:
>>> I'm planning to build the machine with two 1TB 7200 RPM drives
>>> configured in a RAID-0 to maximize throughput on the serial
> reads/writes
>>> that will be required for playback/recording.   I'm thinking that
> this
>>> will be needed for recording (or watching live TV, with a buffer) so
>>> many HD streams simultaneously and also the possibility of streaming
>>> several pre-recorded streams out to the
> extenders/front-ends/browsers.
>>> I've chosen a case with enough space for additional drives for more
>>> throughput/storage-space (just in case it's needed) and/or
> configuring
>>> them as a RAID-1+0 for redundancy, although I don't feel that the
>>> content will really justify a need for redundancy.  As Ben Kamen
> says...
>>> television isn't THAT important (but it's a pretty funny thing to say
> on
>>> a list that is dedicated to recording TV).
>> Just as a point, my current usb 2.0 drive handles 10 HD streams at
>> once just fine (3 writing, 6 flagging, 1 playing).
> Just a follow-up, the most you will ever see out of a single tuner is
> around 36Mbps.  That is recording every broadcast on a single QAM256
> cable channel, which means 3 HD channels, or a dozen SD channels.  For
> pure sequential access, a modern 2TB 5400RPM drive will top out north of
>
> 1Gbps, and won't go lower than 400Mbps.
> _______________________________________________
>
>
> Thanks for the info.  I'm a newbie, so I'm not quite clear on recording
> multiple channels (HD or SD) from a single tuner.  Can someone
> elaborate?

With analog TV, a single channel defined a single video.  There were 
lines of video above and below the visible range that could be used for 
alternate purposes, but it was rather limited.  With digital TV, a 
single channel is a modulated data stream, which can be subdivided 
however the broadcaster chooses.  Broadcast ATSC provides 19.4Mbps, and 
cable QAM just under double at 38.5Mbps.  An HD channel is going to take 
around 12-16Mbps, and a SD channel 2-4Mbps.  You can sometimes find 
channels that are audio only, or with a still image, for a few hundred Kbps.

Broadcasters usually have an HD primary channel, and a SD subchannel for 
weather or movies.  PBS stations often have multiple subchannels, but at 
reduced bitrate and quality.  Since a tuner provides a data stream, and 
not a particular video feed, you can pull multiple video feeds out of 
the stream, and record them individually.  MythTV calls this 'multirec' 
and implements it using virtual tuners.  For now, due to scaling issues 
with the scheduler, as well as hardware issues with the filters on some 
tuner cards, this is soft limited in MythTV to five virtual tuners per 
physical tuner.