[opendtv] Re: [Mp4-tech] Re: HDTV and SDTV Decoders for MPEG-2 andMPEG-4 AVC
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 16 Feb 2005 12:54:18 -0500
It is more a matter of how the STB is designed internally. If the STB
wished to, it could one MPEG stream from the IP multicast that you wish to
cache and send it directly to hard drive, and send a second MPEG stream to
the MPEG decoder for viewing. The cached program is docoded by the MPEG
decoder at a later time when it is viewed. This is, I believe, how PVRs
that are built into DBS STBs operate. So in this case only one MPEG decoder
chip is required, and no MPEG encoder function is required.
If, however, the designer of the STB wishes to give the user an option of
several quality levels as a tradeoff for storage time per Mb, then the MPEG
bitstream would have to be re-encoded at a lower bitrate than the original
multicast. i.e. an original 2 Mbps MPEG multicast is downconvered to a 1
Mbps stream for recording on the hard drive, reducing the video quality but
increasing the number of hours of storage time on the hard drive. I do not
know if this bit rate reduction would require a complete decode-encode
cycle, or if there are encoders that can reduce the bitrate without a
complete decode to baseband video.
Lastly, if the designer of the STB wishes to provide a picture-in-picture
(PIP) function, then I would think that two separate MPEG decoder chips
would be required.
John Shutt
----- Original Message -----
From: "Prashant Desai" <prashant.desai@xxxxxxxxxx>
> but since in case of IPTV there isnt any concept of tuners since it's
> purely on IP multicast so in such case what is required on the STB which
> is
> IP equivelent of STB tuners .....so the user can do both the things at the
> same time that is user can watch the TV and also record the programe at
> the
> same time
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