[mythtv-users] MPEG Hardware decoding

[Edward Wildgoose]

> I am confused about the uses for MPEG-Hardware, be it de- or 
> encoder-chips, by
...
> Take the case of a DVB-input (this is of concern to me because it is what I
> would use). What happens to the data?

The data arrives as an mpeg stream direct from the card.  Myth spools it to disk, then runs it back through an mpeg decoder on demand (ie a bit like piping it into a dvd player program).  So you can now scan back and forwards through the stream *as* it saves down to the HD.  ie it is easy to press pause, come back later and press play because all you are pausing is the player.

As for how the mpeg decoder works, this is mainly done in software and output to a window on the screen in X.  However, there is some support for using a card called a PVR350.  In this case the decoder seems to be broadly working in the same way as before, except that you effectively have a second video card in the pc, choosing to output myth through the "second" video card will result in lower cpu usage because the card can offload some of the mpeg processing requirements.

DVB decoder cards are not supported as an output device, so you will get no decoding benefit from them. (ie get a budget one instead).  However, I notice that there is some new support for running X on a DVB card, so perhaps support will arrive at some point in the future... (don't hold your breath though)

Ed W