Video decoder conflict or something else?

[Daldana]

Hi all, I've been running 1.3.11 on an XP3, 1.7Ghz AMD machine with a Hauppauge 1600 card and have been pretty happy with it, especially on OTA HD channels. I use the HTPC for Live TV, recording, and DVD playback. But of course like most of us who have home built HTPCs, I'm always tweaking for just a little better picture.

I'm using ffdshow as the decoder for the OTA channels and the ATI MPEG decoder for the output from a Directv box (SD). I keep trying to match the output from gbpvr to the output straight out of the Directv box, but just can't quite get there with the ATI decoder so I thought I'd try ffdshow there as well. The picture was markedly better, but when I changed channels back to OTA, those channels lost audio/video sync and became very choppy. I tried as many of the tips for ffdshow setup that I could find in the forums, but nothing worked so I went back to the original ATI/ffdshow config and everything worked fine again. My question is, could using the same decoder for SD and HD channels cause that kind of problem?

Thanks for the info,
Dave

[johnsonx42]

sorry, this isn't any help for you, but a question: how are you specifying a different decoder for SD from the Analog tuner vs OTA HD? Both are MPEG-2, so I'd have thought both would use the same decoder?

[Daldana]

Maybe that's where I have some misunderstanding. I thought OTA HD used the h.264 encoding format so that is where I have ffdshow configured as a decoder.

Dave

[sub]

Maybe that's where I have some misunderstanding. I thought OTA HD used the h.264 encoding format so that is where I have ffdshow configured as a decoder.

Yeah, thats incorrect. In the US everything is MPEG2.

H.264 is used by some countries outside of north america.

[johnsonx42]

Yes, all you are seeing is differences between using the ATI Decoder for MPEG-2, vs. using ffdshow for MPEG-2... whatever you have set for the h.264 decoder is irrelevant in the U.S. My experience with ffdshow is similar to yours; it seems to give fairly decent output on one channel, but changing channels is ugly (it just seems to mix the mpeg-2 stream from the new channel with the one from the last channel until it gets to a reference frame), and it behaves badly when skipping in a recording.

I recommend the Cyberlink PowerDVD decoder. If you don't have it on a CD that came with a DVD drive (that's where I got mine), you can download it with the K-Lite Codec Pack (but when you install one of those codec packs, it's best to install only what you know you want... the default 'kitchen sink' approach of the installer is not such a great idea). I've also seen some download links posted here and there in the forum. I imagine though any method of obtaining the codec other than from a legit PowerDVD disc (or other cyberlink product) is not legal.

Since you have a Hauppauge card, you can also install the WinTV app from the CD and get the 'Intervideo Non-css decoder for Hauppauge'.

[Daldana]

Thank you for the information gentlemen. I do have the PowerDVD decoder (albeit an older version-6) and the NonCSS decoder which both work just as well as the ATI decoder. Unfortunately none of the above will generate a picture quality match to that coming straight out of the directv box, which is the only thing holding down a good WAF. She loves the picture quality on the OTA input, so I guess I'll keep plugging away to see if I can find a way to up the picture quality coming from the S-video input.

Thanks again for your help.

Dave

[johnsonx42]

I guess I'm surprised you see much difference between decoders on the analog side. Normally the quality of the analog side is dictated by the capture card, since it has to digitize the analog signal, and then encode it to mpeg-2; much can be lost or changed in that process. That's why the final output may look significantly different than the original. After that, the decoder shouldn't make all that much difference. I believe you that you get a better output with ffdshow, but I don't know why that should be the case.
Have you investigated different quality settings for the analog capture device?

[Daldana]

The Hauppauge 1600 has both digital (OTA) and analog (S-video) inputs so I have two capture devices setup in gbpvr's config. I have the directv stb sending the analog signal via the S-video input to the 1600 on a manually setup channel 1. The other OTA channels are setup in the digital capture device with their own channel numbers. The HD OTA channels look great.

The TV set has an composite input which is also connected to the directv stb, this is where I see a big difference in picture quality. When viewing a channel through gbpvr, the quality is not as good as when I view the same channel straight from the directv stb. I'm at a loss as to why the quality is so different.

Dave

[johnsonx42]

The TV set has an composite input which is also connected to the directv stb, this is where I see a big difference in picture quality. When viewing a channel through gbpvr, the quality is not as good as when I view the same channel straight from the directv stb. I'm at a loss as to why the quality is so different.

I'm not surprised you see a big difference in quality comparing that way; your HVR-1600 receives the analog signal, digitizes it frame-by-frame, and passes those frames to an on-board MPEG-2 encoder. That MPEG-2 program stream is then passed to GB-PVR, which passes it to a decoder and then on to the renderer which puts it on screen. Much can be lost in that process. This is where the quality settings on your analog capture device can make a big difference.

I'm not quite sure what to make of your situation though; your original post said you got much better quality when you had ffdshow set as your MPEG-2 decoder. Yet you say the various decoders give you about the same quality on OTA digital channels. This runs counter to expectation, since both types of signal are MPEG-2, so the decoders should perform roughly the same between the two. I guess I should just bow out of this conversation, since it's not adding up to me and beyond increasing the quality level on your analog capture device, I don't know what else to suggest.

[Daldana]

That's exactly what I was trying to figure out too! When the decoder is set to ffdshow, the picture quality from the stb looks much better but OTA HD starts stuttering and loses audio/video sync.

The biggest difference I see seems to be in the contrast which really affects the clarity, everything looks a bit fuzzy around the edges.

I changed the quality settings in the analog capture device to high quality, but I don't see much change. I will keep trying and if I find something that does make a difference, I'll post it. Thanks again for your help.

Dave