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Fast Forward in HR23 vs HR24

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by jimmie57, May 28, 2013.

  1. jimmie57

    jimmie57 Hall Of Fame

    Jun 26, 2010
    Texas City, TX
    It appears to me that the HR24 shows a lot more frames as it Fast Forwards in FF2 than my HR23 did. The HR23 was super jerky when you went to FF2 and the HR24 just seems to speed up.

    Is it just my imagination ?
  2. TomCat

    TomCat Broadcast Engineer

    Aug 31, 2002
    Maybe not.

    The reason you see 30 fps on SD in FFWDx2, for instance, and about 5 fps in HD, is because it takes more horsepower to decode MPEG4 than it does MPEG2. There is enough headroom to decode MPEG2 at a rate twice that of what is delivered in real time, but not enough to do that for MPEG4. And of course in FFW this implies decoding the video faster than real time if possible, But if the horsepower just isn't there the design has to revert to a lower frame rate on output, probably just decoding the I frames and P frames and discarding the B frames, or maybe only some of them.

    This implies that as decoders get faster/better. that maybe they will indeed be able to use a higher frame rate on FFWD. The 24 is newer, and maybe the decoder chip is improved in that regard (I don't have one for comparison, sadly). I had long ago predicted that this (more fps and possibly 30 fps on FFWD) will be the normal state of affairs some day; I just can't predict when.

    Improvements in PQ by virtue of a better decoder chip will not be forthcomng, however, because the PQ is fixed at the uplink.

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