Recording quality vs Monitor resolution...

[Tander]

I'm fairly new with Sage, and this may be a dumb question... but is there an easy way to figure out what the lowest recording quality you can use is that matches the maximum resolution of your monitor?

I.E., there's really no point in recording at a level that is twice the resolution of your monitor, since you'll never see it. (Or will you?)

As an example, my monitor's maximum resolution is 1280 x 1024 at 60 Hz, and supposedly capable of 1360 x 768. I've been recording my shows at Max Quality, Mpeg-2 PS, which works out to around 5.9 Gigs an hour.

Is there a formula or easy way other than visual to determine just how low I can go down in recording quality before I start to get below the Max of my monitor? I figure there is no point in overkill.... but want to match my capabilities.

[flavius]

You are the judge of what's acceptable.

Just try downgrading recording quality.. I ended up with DVD Standard Quality for most of my recordings.

[Tander]

Thanks .... I've been trying that, and will be doing more later. (The DVD level was my next stop)... but I was hoping there was a scientific way... ie., maximum pixels that can be shown, versus number of frames/pixels captured... looks like I'm back to watching / recording /watching / recording... cleaning my glasses...

[BobPhoenix]

Recording quality is bits per second not number of pixels on the screen. So for the same class of recording qualities the number of pixels is the same no matter what recording quality you pick. What I mean by class is all of the DVD quality recordings and max mpeg have the same size they are rated 480i whereas the VCD quality recordings are half of that - 240 I think.

[flavius]

This is only true if one likes the PQ

[Tander]

I guess I'm confused then... (Sorry for the pixel reference, I'm an old NASA guy who use to work with digital imagery) ... so back then max resolution was determined by pixel size and total number of pixels. I do understand in this case, the pixel size is fixed.

But I'm watching TV in HD, where the info being captured is supossedly 1080i... my monitor obviously won't handle true 1080i... but I was trying to figure out the recording level that closely resembles my monitor. I would assume that the more bps I can throw at the monitor, the better, up to a point where it doesn't do any good. But like I said, I'm new to digital TV.

Back to watching and testing... but thanks for the input.

[Opus4]

If you are recording digital TV, then the recording quality settings don't do anything because the tuner is simply saving the digital stream that it receives. In this case, stop testing because you won't see a difference from one setting to the next.

If you are recording analog TV, then you pretty much test the quality settings as mentioned above to see which one is good enough for you, since there is no correct setting.

- Andy

[Tander]

Thanks Andy! Now that makes sense! I'll stop cleaning my glasses and testing... and get back to watching.

If I understand you correctly, the digital stream is simply captured and recorded,... and then re-streamed back. However, there are "Quality" settings for the digital capture and playback... so I'm assuming the real driver or reason for changing those is to match the ability of your system to smoothly push it all thru the pipeline...

Thanks again for the input.

[jbarr]

But isn't this completely dependent on the capture method/device? For example, I use two PVR-150's--one recording raw analog from coax, and the other recording via RCA connections from an STB. Though the STB receives and processes digital video, output to the PVR-150 is still analog. Yes, the digital stream from the PVR-150 is being recorded and played back, but doesn't SageTV's recording qualities "tell" the PVR-150 what quality to use? In the end, it's analog to digital, not true digital.

On the other hand, in the case of my HDHomeRun box, it is capturing the digital stream.

[nielm]

To summarize several replies:

Sage captures analogue SDTV by sampling it ay 720x480x30fps (interlaced), encoding that into an MPEG2 stream at the bitrates set using the quality settings, ans saving it to disk. The capture resolution is fixed, the bitrate determines how much information is 'lost' during the encoding process.

Sage captures digital HDTV by recording the digital stream sent by the broadcaster at the resolution and bitrate that the broadcaster used to encode. As Andy mentioned, quality settings are useless -- it may be considered to be a UI oversight that capture qualities can be specified for digital tuners

At playback, the captured streams are decoded, deinterlaced, rescaled to your desktop resolution (taking into account aspect ratios) and displayed.

If you have a LCD or plasma display, then the best solution would be to have the desktop resolution being the native resolution of the display, so that further rescaling does not have to be done by the display.

[jbarr]

neilm, thanks for the explanation. It sums things up nicely.

Now, I don't mean to nitpick, but can you please clarify when you say, "Sage captures"? Do you mean that SageTV does the capturing, or that SageTV instructs the capture device how to capture? I know this may seem like splitting hairs, but if I understand correctly how this all works, SageTV is not actually capturing, but just "managing" the capture and playback. Or am I going too deep with this?

[jbarr]

Originally Posted by nielm

If you have a LCD or plasma display, then the best solution would be to have the desktop resolution being the native resolution of the display, so that further rescaling does not have to be done by the display.

Which, if the captured file is SDTV (or more precisely, not widescreen) then the ideal resolution would be 720x480 (which would obviously not be a widescreen image.)

[camus]

Originally Posted by jbarr

Which, if the captured file is SDTV (or more precisely, not widescreen) then the ideal resolution would be 720x480 (which would obviously not be a widescreen image.)

I think that is more applicable to setting your GPU's resolution to match your displays resolution, not the video's resolution. That way when the video signal sent to your display, the display is not scaling it again.

[Opus4]

Originally Posted by jbarr

Now, I don't mean to nitpick, but can you please clarify when you say, "Sage captures"? Do you mean that SageTV does the capturing, or that SageTV instructs the capture device how to capture?

"Sage captures" is just shorter than typing "Sage tells the capture device to capture".

Originally Posted by jbarr

Which, if the captured file is SDTV (or more precisely, not widescreen) then the ideal resolution would be 720x480 (which would obviously not be a widescreen image.)

LCDs have a native resolution (it has a specific # of pixels it can display) & anything sent to it at a different resolution has to be scaled to fit the number of pixels the LCD screen has. To prevent this scaling step, the Windows display resolution should match the LCD's native res.

- Andy

[nielm]

Originally Posted by jbarr

Now, I don't mean to nitpick, but can you please clarify when you say, "Sage captures"? Do you mean that SageTV does the capturing

Ok, Ok Sage instructs the device to capture the required channel with the required parameters, Sage receives the resulting encoded stream (maybe post processes it, eg for digital TV transport streams) and saves it to disk

Originally Posted by jbarr

Which, if the captured file is SDTV (or more precisely, not widescreen) then the ideal resolution would be 720x480 (which would obviously not be a widescreen image.)

Thats the capture res. I was talking about the resolution of the display device.

720x480 MPEG2 can be anything: 4x3 video, 16x9 anamorphic video (from a cable/sat STB) or 16x9 letterboxed into a 4x3 video. It will always be resized to the correct aspect ratio before display.