DVB-T need mpeg encoding?

Discussion in 'Amateur Video Production' started by Tim, Sep 7, 2004.

  1. Tim

    Tim Guest

    I thought I had found a perfect tv-card for my project (building a Myth pvr)
    with Hauppauge PVR 350, both hardware encoding and decoding, it even has
    good Linux support and a remote.

    It was all fun and games untill I realized that I want a card that supports
    digital TV (DVB-T). I could find 19 DVB-T cards on
    http://www.videohelp.com/capturecards.php but neither if them supports
    hardware mpeg encoding/decoding.

    Is that because the digital streams are already mpeg so there is no need to
    encode it? Or have I just not found the right card?

    I am trying to turn my p200mhz into a pvr so I need to do as much as
    possible in hardware (I actually want to use the p200 to a few other things
    at the same time).

    Should I maybe buy one DVB-T card and one encoder/decoder card? Is that the
    trick?

    Any pointers are much apreciated.

    Tim
     
    Tim, Sep 7, 2004
    #1
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  2. Tim

    Jukka Aho Guest

    DVB transmissions (regardless of whether it is DVB-T, DVB-C
    or DVB-S) are based on MPEG-2. What you get from the card
    is an MPEG-2 transport stream (usually containing several
    multiplexed audio and video streams, grouped into tv or
    radio programmes.) In other words, the MPEG-2 encoder is
    at the broadcaster's end; you are just receiving the
    already-encoded MPEG-2 data with your card.

    However, some DVB cards _do_ have a built-in MPEG-2
    _decoder_ chip, alongside with a video encoder and an
    analogue video output ("tv out") connector. These are
    usually called "full-featured" cards, while those cards
    which can only receive the raw transport stream are
    called "budget" cards.

    Full-featured cards are usually a preferred choice for
    hobbyist DIY PVR projects, since the software support
    for them is somewhat better and the connection to the
    tv is less problematic (as they have a "tv out" on their
    own and you do not need to fuss about with the "tv out"
    on the primary VGA display adapter card which may have
    problems with scaling, interlacing etc.)

    Here you have one example of a full-featured DVB-T card
    ("Technotrend DVB-T 1.2 Premium Edition"):

    <http://www.technotrend.de/english/products/pcproducts2-1.html>
    <http://www.technotrend.de/english/products/pcproducts2-2.html>
    You need to have an MPEG-2 decoder in hardware (one way or
    the other); a 200 MHz Pentium is simply not fast enough for
    software-based, real-time MPEG-2 decoding.
    Yes, that is another way of achieving the same result. Some
    people have used "budget" cards together with a separate
    hardware MPEG-2 decoder / "tv out" card (such as "Hollywood
    Plus DXR3", which was originally sold for decoding MPEG-2
    data from DVDs.)

    You might also want to see

    <http://www.linuxdvb.tv/>
    <http://www.linuxdvb.tv/software/apps/vdr-l.jpg>
    <http://www.flood-net.de/flood/projects/vdr-progress.jpg>
    <http://www.linuxtv.org/>
    <http://www.cadsoft.de/vdr/>
     
    Jukka Aho, Sep 7, 2004
    #2
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  3. Tim

    Tim Guest

    <snip a milion interesting things>

    Sweet! That was a very informative answer. I will read it over a couple of
    times and look at all the links, I am pretty sure I got all the info I need
    for the next few weeks.

    Thanks a lot

    Tim
     
    Tim, Sep 7, 2004
    #3
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