Which decoders are used for live TV?

[Chris King]

As I understand it GB-PVR depends on there being a hardware mpeg2 encoder on the card, or USB2 device. If so, which decoder(s) does GB-PVR use for live video and in what sequence? If the transport stream is already in mpeg2 why can't this just be displayed directly on screen, rather than needing an H.264 decoder filter?

What is the sequence of filters the video stream goes through, from incoming digital TV to screen rendering?

I'm trying to understand this to get a handle on CPU usage, as my machine freezes in live TV in GB-PVR after a few minutes, probably from CPU overload, although its dual core and I need to know which filter is critical to on-the-fly decoding, and how it recognizes the graphics card etc. in a given machine.

[sub]

As I understand it GB-PVR depends on there being a hardware mpeg2 encoder on the card, or USB2 device. If so, which decoder(s) does GB-PVR use for live video and in what sequence?

The requirement to use a hardware MPEG2 encoder is only related to analog cards. Digital cards just recording the already-encoded transport stream transmitted by the broadcaster.

If the transport stream is already in mpeg2 why can't this just be displayed directly on screen, rather than needing an H.264 decoder filter?

The transport stream data arrives as encoded MPEG-2/H.264 video and AC3/HE-AAC/MPEG1-Layer2 audio. To display the video, the PC has to decode this information back into a picture that can be displayed on the screen. This job is done by a video decoder filter. It either does all the decoding work itself, or if the video card supports it then it can hand off much of the decoding work to the hardware acceleration support of the card. After this a frame of video has been decoded and is ready to be displayed on the screen by the video card.

You cant "not decode" the picture. Screens show pictures (bitmaps). If you tried to treat a transport stream buffer as a bitmap you'd just see garbage.

What is the sequence of filters the video stream goes through, from incoming digital TV to screen rendering?

The data comes from the capture card, is passed into the microsoft demultiplexer to split it into separate audio and video streams, then each of those streams pass the data through the appropriate type of decoder to a renderer. For example, H.264 video could go through the Cyberlink H.264 Decoder to the VMR9 Renderer.

[Chris King]

Thanks a million - that's great!