[mythtv-users] Always use the HD PVR and retire my PVR 250, or continue to use both in same recording group

belcampo belcampo at zonnet.nl
Sat Jun 26 17:36:12 UTC 2010

John P Poet wrote:
> On Sat, Jun 26, 2010 at 5:21 AM, belcampo <belcampo at zonnet.nl> wrote:
>> James Orr wrote:
>>> On Fri, Jun 25, 2010 at 10:19 PM, John P Poet <jppoet at gmail.com
>>> <mailto:jppoet at gmail.com>> wrote:
>>>    On Fri, Jun 25, 2010 at 8:13 PM, Yeechang Lee <ylee at pobox.com
>>>    <mailto:ylee at pobox.com>> wrote:
>>>     > John P Poet <jppoet at gmail.com <mailto:jppoet at gmail.com>> says:
>>>     >> If the quality via the HD-PVR is lower, you probably have the
>>>     >> bitrate on the HD-PVR set too low.
>>>     >
>>>     > Speaking of bitrates, how optimal are the settings in the default
>>>     > HD-PVR recording profile? Is there room to tweak them, or are they
>>>     > about as good as VBR bitrates for the device can get?
>>>    I am not even sure what the current defaults are.  I have been using
>>>    my HD-PVRs since before Myth had defaults for the HD-PVR :-)
>>>    As far as what the defaults should be, that is a good question.  I
>>>    would assume most people using the HD-PVR are more concerned with
>>>    quality than file size.  Personally, I use max bitrate VBR by default,
>>>    and max bitrate CBR for "high quality" (e.g. sports events).
>>> That's actually a good idea, though I'd probably do it the other way
>>> around (CBR for shows/movies and VBR for sports and maybe documentaries).
>>> The defaults on the HD-PVR were ...
>>> Low Avg - 4,500, Low Max - 6,000
>>> Med. Avg - 9,000, Med. Max - 11,000
>>> High Avg. - 13,500, High Max - 20,200
>> I partially agree, I/me/myself don't see any use for CBR, unless you have to
>> fit some recording a finite-size, CD/DVD, device and are not able to
>> calculate/educated-guess a reasonable avarage bitrate. Choosing CBR, which
>> you have to do in front, it'll always be too much or too little, unless you
>> can read the future, which none of us is able to, AFAIK.
>> VBR with quality settings as with x264/ffmpeg is the only setting, unless
>> you have to 'fit it on a certain device' that makes sense to me.
>> The HD-PVR lacks such a setting AFAIK, so you'll have to make an educated
>> guess of what would be the minimum-bitrate for the quality you want, and let
>> the HD-PVR raise the bitrate to an available max of 20Mb/s, by using VBR, if
>> there is need for that.
>> By choosing CBR you are more or less 'limited' to 13.5Mb/s.
>>             video_bitrate_mode (menu) : min=0 max=1 default=1 value=1
>> flags=update
>>                  video_bitrate (int)  : min=1000000 max=13500000 step=100000
>> default=6500000 value=6500000
>>             video_peak_bitrate (int)  : min=1100000 max=20200000 step=100000
>> default=9000000 value=9000000 flags=inactive
> Actually, even with VBR, the HD-PVR maxes out at 13.5 for all
> practical purposes.  It's ability to record at a higher bitrate than
> that, for VBR, is *extremely* short lived 
It's there for the short-living high-motion-event, how it's supposed to be.
> -- it cannot maintain it.
In most cases doesn't have to.
> The absolute highest quality you can get out of the HD-PVR is CBR at
> 13.5.   VBR will always produce a lower *average* bitrate than CBR.
> The HD-PVR's VBR mode looks for a way to turn-down the bitrate when a
> high bitrate is not needed.  It can turn-up the bitrate past 13.5, but
> only for a very brief amount of time.  it does a good job of balancing
> file size with quality.  That is why I use it as my default -- get
> good quality while keeping the file size under control.
> John

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