[mythtv-users] Suggested Encoding Rates

[Andrew Close]

On 4/28/05, Ian Trider <iantri at gmail.com> wrote:
<snip/>
> NTSC is analog -- the number of vertical scanlines is fixed at 525, of
> which 486 are visible, or  for convenience sake when dealing with
> MPEG-type encoding algorithms (which work on blocks of 16) 480.
> 
> Horizontal 'resolution' is dependant on a variety of factors; source,
> method of transmission, receiving equipment, etc.  You should be able
> to capture (given that the capture card is of high quality) as much
> detail as possible from the source (if it is a high-quality picture
> from a local station received by antenna) with a resolution of
> 540x480.  If you are on cable, depending on the quality of your cable
> system,  480x480 should capture full detail.
> 
> Satellite is a different matter.  Systems like Bell ExpressVu,
> Starchoice, Dish and DirecTV   are encoded already into MPEG-2 format,
> usually at a resolution of 480x480 on the regular channels, at (IMO) a
> far too low bitrate.  However, because the receivers only have analog
> outputs, that signal is converted back to analog NTSC and recaptured
> by MythTV -- capturing at 480x480 probably won't quite capture the
> entire resolution, but it's a lost cause, anyway.
> 
> 352x480 will give you something approximately equivilent to a
> excellent VHS recording at SP mode.
> 
> Anythingx240 will be discarding have the scanlines vertically, and
> will look terrible.
> 
> Resolutiion does not affect file size, bitrate does.  However, if you
> reduce the resolution, the encoded image will be more similar to the
> source in terms of artefacts.  This is because there are fewer pixels
> to be compressed into any given bitrate.
> 
> Also a restriction you should note is that if you want to go to DVD
> without reencoding, you are limited to the resolutions 352x240,
> 352x480, 704x480 and 720x480.
> 
> My personal opinion on the matter of 'what is acceptable quality':
> 
> I capture everyday recordings at 352x480, with a bitrate of 3150kbps.
> Some minor artefacts are visible in the image, comparable to satellite
> (if you consider satellite quality to be acceptable, this bitrate
> should be fine for you).
> 
> My "high quality" setting is 720x480 (yes, this is overkill, but
> necessary if you want to go to  DVD) at a bitrate of IIRC 6200kbps.
> This should yield an acceptable image, with almost no visible
> artefacts when viewed on an SDTV.  (think premium satellite channel).
> 
> You might find this chart interesting:
> http://www.mediachance.com/dvdlab/tutorial/bitrate.html
> 
> .. though because the Hauppauge cards do not have the benefit of being
> able to do 2-pass encoding (and the encoder, while good, is not the
> best), you'll find that you'll need a slightly higher bitrate than the
> chart indicates.  For example, I consider 3150kbps to be on the low
> end of good at 352x480 when encoded with the PVR-350).

Ian,

thanks for the info! :)  that's exactly what 'i' was looking for.  i'm
sure Jason and several others will also appreciate the quantitative
data you've provided as well.

thanks again.