[mythtv-users] CBS/NBC 1080i and telecine

Yeechang Lee ylee at pobox.com
Fri Jul 17 03:50:35 UTC 2009


Andrew Gallatin <gallatin at cs.duke.edu> says:
> You keep talking like there is a problem on the broadcaster's side
> ("clean", "guilty party").  There isn't.  What they're doing is
> completely legal, its just that MythTV doesn't seem to understand
> it.

I didn't mean to imply that the broadcasters in question were
violating an actual regulation, as far as I know. That said, the
streams are flagged incorrectly, unless there is a good reason I am
unaware of for why "progressive" and "interlaced" frames are
intermixed every few frames in the affected broadcasts. The
problematic flagging does not come from the source material, as its
existence varies by show and by episode, apparently determined by
contemporary bandwidth-shaping needs on the broadcaster's part; I have
seen many cases in which HDNet Movies will show a given movie without
issues, unlike (say) Showtime HD.

> From what I understand, its very uncommon for software handle this
> correctly.  I'm just hoping VDPAU will play these files back
> correctly..

The issue is unrelated to VDPAU or to graphical horsepower, or the
lack thereof. VDPAU offloads to the GPU the graphical decoding,
rendering, and deinterlacing duties that, for MythTV, the CPU has
traditionally handled. That's it. Yes, VDPAU's deinterlacers are
extremely good (both in and of themselves, and in the sense that the
offloading often permits the use of most-sophisticated deinterlacers
than would be possible otherwise). VDPAU does not, as far as I can
tell, make a meaningful difference in terms of this particular issue,
however, as it arises solely from MythTV frantically switching between
deinterlacing and not deinterlacing multiple times a second as it is
told to. The aforementioned patches simply tell mythfrontend to ignore
progressive-frames flags during playback once it sees an interlaced
flag; in other words, ignorance is bliss from the MythTV
perspective.[1]

You asked about video quality comparable to that of a Sigma-based
Network Media Tank. I have never owned one so cannot say firsthand;
someone like Brian Wood would be able to compare. I am more than
satisfied with the performance of VDPAU's Temporal 2x deinterlacer,
but Jean-Yves Avenard and others have spoken of the Advanced 2x
deinterlacer (which my 8400GS video card can't handle) as being even
better.

[1] Now that I think about it, I suspect that NMTs and other settop
boxes that don't have issues with the broadcasts in question simply do
the same thing as the patches do, and ignore the flags when they don't
make sense.

-- 
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