Cablecard tuner video quality

[Dargason]

Is there any difference in video quality of cablecard tuners?

I thought they basically just 'tuned' into a digital stream, decrypted it, and passed on the results to the software. No encoding or decoding.

I ask because it seems like my cable set-top box image quality is better than my HD300 playing a cablecard recorded show.

[mguebert]

Originally Posted by Dargason

Is there any difference in video quality of cablecard tuners?

I thought they basically just 'tuned' into a digital stream, decrypted it, and passed on the results to the software. No encoding or decoding.

I ask because it seems like my cable set-top box image quality is better than my HD300 playing a cablecard recorded show.

I would think it is more in the difference between the way the output is processed on the STB and the HD300.

[drewg]

Originally Posted by mguebert

I would think it is more in the difference between the way the output is processed on the STB and the HD300.

Or even just something as simple as different settings on different TV inputs. When I had my TV calibrated, the calibrated settings at first only applied to HDMI-1 where the BD player the calibrator used was. We then copied the settings to all inputs..

Drew

[Dargason]

I'm bumping this because I'm still not convinced the quality is the same.

Last night I was looking through some recordings and came across one that I looked at and thought "hey, that's a good picture" and it turns out it was recorded by the HD-PVR last January. Unfortunately, rebuilt my server last spring and never set up the HD-PVR because the cablecard tuner is so much more reliable.

But it's always seemed to me that there is a lot more pixelation in fast-moving scenes than there used to be. I'm really tempted to set up my HD-PVR again and try recording a show with both the HD-PVR / set-top box and the cablecard tuner. Just to prove to myself I'm not crazy.

If true, the only explanation I can come up with is that the STB renders the original source material better than the HD300. Then the HD-PVR captures the superior image produced by the STB and encodes it into a format that the HD300 handles well.

I know it's all still h.264, but I imagine there are more advanced and less advanced versions... and my provider may be outputting a version that relies on more client horsepower than the HD300 has.

Speculating even further, if this is true, then it might be possible for my server to re-encode the cablecard files losslessly into a format more like what the HD-PVR creates... and thus improve my video quality.

Am I crazy or does some of this make sense? (I suppose those things aren't mutually exclusive, though.)

[panteragstk]

The stream the cable card gets should be identical to what the stb outputs unless there are picture settings on the stb. If there are, you can set the same settings on your TV to improve video quality. That should be it AFAIK

[Dargason]

I'm not comparing the quality of the CC tuner to what I would get if I connect the STB direct to the TV. I'm comparing it to what I get when I record the analog output of the STB using the HDPVR and then stream that recording to the HD300 for display on the TV.

In both cases, the TV is seeing output from the HD300. The only difference is whether the file was encoded by the HD-PVR or simply saved by the cablecard tuner.

[darcilicious]

IIRC, the recording quality setting is on a per tuner basis and I'm not sure what the default is; have you made sure it's set to "best" for the CC tuner?

[panteragstk]

Originally Posted by Dargason

I'm not comparing the quality of the CC tuner to what I would get if I connect the STB direct to the TV. I'm comparing it to what I get when I record the analog output of the STB using the HDPVR and then stream that recording to the HD300 for display on the TV.

In both cases, the TV is seeing output from the HD300. The only difference is whether the file was encoded by the HD-PVR or simply saved by the cablecard tuner.

I know. What I'm saying is that some STB's have picture settings that could effect PQ when recorded by the hd-pvr where the cablecard won't have those settings.

[wayner]

Maybe it is also an issue that the HD-300's decoder for H.264 files is giving a better, or at least cleaner looker picture than what you get from the MPEG-2 decoder? Perhaps it deals better with stuff like deinterlacing and pixelization.

[Dargason]

I know. What I'm saying is that some STB's have picture settings that could effect PQ when recorded by the hd-pvr where the cablecard won't have those settings.

Hmm... it's been a long while since I actually used the STB interface, but I can check for picture quality settings. I seem to remember not finding anything when I went looking for a way to 'fix' the output to 720p but I might be remembering a different box.

the recording quality setting is on a per tuner basis and I'm not sure what the default is; have you made sure it's set to "best" for the CC tuner?

The quality settings don't apply to cablecard tuners... my understanding is that the card just decrypts the incoming stream and saves it to the hard disk. (I think it also re-encrypts it before saving depending on the DRM flag, but that's not relevant to this discussion.)

Maybe it is also an issue that the HD-300's decoder for H.264 files is giving a better, or at least cleaner looker picture than what you get from the MPEG-2 decoder? Perhaps it deals better with stuff like deinterlacing and pixelization.

I'm not sure I understand which MPEG-2 decoder you mean... these scenarios are all entirely hardware decoding (in the STB) or hardware decoding in the HD-300. At least I assume the STB uses hardware decoding... it would be pretty stupid if it didn't.

But my hypothesis is that the decoder in the STB does a better job than the HD300 given the flavor of h.264 that my provider supplies.

It's got me thinking though, that it might be interesting to play around with software decoding on my PC using the 'bad' recordings to see if I can make them look better than what I get from the HD300. I think it would support the idea that the decoder makes a difference and that re-encoding the files might have some value.

[wayner]

Originally Posted by Dargason

I'm not sure I understand which MPEG-2 decoder you mean... these scenarios are all entirely hardware decoding (in the STB) or hardware decoding in the HD-300. At least I assume the STB uses hardware decoding... it would be pretty stupid if it didn't.

I mean the hardware decoder chip in the HD300 - maybe it does a better job with H.264 than MPEG-2.

But you're right that it could be a better decoder in the STB as well.

[Tiki]

The cable card tuners capture the digital stream exactly as it is sent from the cable company. The HD-PVR re-encodes the analog signal that has already been decoded by the set top box (STB). Therefore it is impossible that the HD-PVR recordings could be better than the cable card tuners (though they may be so close in quality that they are indistinguishable).

However, there is another possibility. When using the HD-PVR, most people found it necessary to fix the output resolution of the STB (usually to 720p). The HD-PVR would then encode the recording at that same resolution. The Cable Card tuners on the other hand, do no fix the resolution - they record at whatever resolution is being broadcast.

By default, the Sage Extenders (HD300), output at a fixed resolution (unless you manually enable Native Resolution Switching). If you have your HD300 set to 720p and all your HD-PVR recordings are 720p, it doesn't have to do any scaling. Your TV might do some scaling, but most newer HDTVs have very good scalers. But, your Cable Card recordings will be a mix of resolutions depending on which channels you are recording from. It's possible that the HD300 needs to re-scale some of those recordings (1080i to 720p) and doesn't do as good of a job as the scalers in your STB and TV.

You might want to look at the recording details on some of your files and see which tuner recorded it and what the video resolution is. You may also want to experiment with the native resolution switching option in the extender.

[Dargason]

I mean the hardware decoder chip in the HD300 - maybe it does a better job with H.264 than MPEG-2.

Ok, now I see the confusion. I had assumed that the feed was h.264, but I guess that's not necessarily true.

Video standards always make me feel stupid.

The cable card tuners capture the digital stream exactly as it is sent from the cable company. The HD-PVR re-encodes the analog signal that has already been decoded by the set top box (STB). Therefore it is impossible that the HD-PVR recordings could be better than the cable card tuners (though they may be so close in quality that they are indistinguishable).

While I understand this in theory, it's only 'impossible' if you assume all decoders produce output that is equivalent, given the same input. Consider an extreme case where the STB does a perfect reproduction (given the limitations of the input stream) while the HD300 does a terrible job. In this case, it could be possible for the HD-PVR to re-encode the STB output into a format that the HD300 does a better job presenting.

By default, the Sage Extenders (HD300), output at a fixed resolution (unless you manually enable Native Resolution Switching). If you have your HD300 set to 720p and all your HD-PVR recordings are 720p, it doesn't have to do any scaling. Your TV might do some scaling, but most newer HDTVs have very good scalers. But, your Cable Card recordings will be a mix of resolutions depending on which channels you are recording from. It's possible that the HD300 needs to re-scale some of those recordings (1080i to 720p) and doesn't do as good of a job as the scalers in your STB and TV.

I don't think was ever able to fix the STB output to 720p, but as I said, it's been a while since I looked. I'll also check the native resolution switching setting.