#21 Transcoded B-frames broken (mpeg2movie)

closed-out-of-date
nobody
None
5
2003-04-18
2001-05-20
No

Hiya! Good work on mpeg2movie. All of the Heroines'
projects are exciting, but I find this one the most
useful and groundbreaking!

Anyway. I find that in mpeg2movie 1.5 and 1.4, the
encoding of B-frames works from a quicktime source but
is broken from mpeg (1 or VOB) sources.

The brokenness manifests itself in the form of many
blank solid-green frames in the output mpeg and many
frames out-of-order.

No command-line options fix this apart from disabling
B-frames (-n 0). -n 1 and -n 2 exhibit the bad
behaviour. -n X where X>2 crashes but this is
user-error as mentioned elsewhere.

Regards,
--Adam

Discussion

  • Heroine Virtual

    Heroine Virtual - 2001-05-26
    • summary: Transcoded B-frames broken (mpeg2movie)
      --> Transcoded B-frames broken (mpeg2movie)
     
  • Heroine Virtual

    Heroine Virtual - 2001-05-26

    Logged In: YES
    user_id=83549

    It should be broken for transcoding. The origin of the
    problem is a
    bit more complicated but well known. Think of how the b
    frames work and
    what you have to know before you can decode a b frame. You
    need to
    know the preceeding and following P frames. Now when you
    encode an
    mpeg stream you're really encoding frames out of order so
    when they're
    played back they'll show up in order.

    If you encode the frames sequentially they'll play out of
    order.
    Encoding frames out of order requires reading them out of
    order which
    Quicktime does well but DVD's can't do without a lot of
    work. Interest
    in playing movies on general purpose computers has died off
    enough that
    it probably will never be implemented in a desktop program.
    The last
    desktop PC was sold in some store in Nebraska a long time ago.

     
  • Adam D. Moss

    Adam D. Moss - 2001-06-20

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    user_id=224045

    Okay. Would it be hard to buffer as many
    input frames as is needed to output a B-frame?
    Then you wouldn't be randomly-seeking; it
    would be a sequential read but of more than
    one frame.

    (n.b. I am not doing anything to do with DVDs
    anyway!)

     
  • Heroine Virtual

    Heroine Virtual - 2003-04-18
    • status: open --> closed-out-of-date
     
  • Heroine Virtual

    Heroine Virtual - 2003-04-18

    Logged In: YES
    user_id=83549

    Forget about encoding B frames. The quality is worse.

     

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