[mythtv-users] HD PVR: What does "13.5 Mbps" mean?

[Steven Adeff]

On Sat, Apr 5, 2008 at 10:36 AM, Willy Boyd <willyboyd at gmail.com> wrote:
> On Sat, Apr 5, 2008 at 12:31 AM, Yeechang Lee <ylee at pobox.com> wrote:
>  [snip]
>
> >  h.264 files it spits out? If the former, what does this imply about
>  >  the device's ability to properly capture the full breadth of 1080i
>  >  19.39Mbps input?[1] If the latter, is a 13.5Mbps h.264 recording
>  >  really sufficient to capture the full quality of 19.39Mbps MPEG-2?[2]
>  [snip]
>
>  I've always thought that any recompression is never really sufficient
>  to capture the full quality of the source.  However, h.264 usually
>  carries the same quality at lower bitrates, so I could see 13.5Mbps
>  still looking very good for anything coming out of your cable box.
>  I'm not sure how bad that would compare to Bluray source, as I don't
>  own a player yet.

except that BluRay/HD-DVD are h264 to begin with, and like the OP
pointed out, at a much higher bitrate. BUT also remember that
broadcast HDTV is currently MPEG2, so the color depth is much lower
than BluRay and the compression level is "higher" (different really,
but basically less bits per pixel are reserved than on the h264 used
for BluRay).

So the bitrate for h264 used by the HDPVR is more than sufficient to
get very very close to the quality level of the original broadcast,
though, of course, due to the D->A->D steps required, won't be as good
as capturing via QAM or Firewire (which is just capturing the original
MPEG2 stream).

-- 
Steve
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