>Hi all
>I have something odd here.
>
>I get my footage in XGA (1024*768) Mov (422 uncompressed using libquicktime).
>
>If I transform these mov in dv files such as :
>
>qttoy4m my_super8.mov | y4mscaler -O CHROMASS=420jpeg \
>| y4mtoppm | \
>| ppm2raw -a -2 > my_super8.dv
>
>Well... it works despite no indications regarding the scaling, it cant be by
>default since the choice of NTSC or PAL needs to be asked somewhere..
Oh, man, I can't stop laughing!
(Just kidding :) --- I'm not really laughing. I'm actually weeping a little.)
(Really... just kidding. At best/worst, just a little chuckle.)
y4mscaler isn't doing any frame-size scaling in this case, but it may
be doing to chroma-mode conversion. (The informative output will tell
you everything it's doing.) y4mscaler will try to guess PAL/NTSC from
the input framerate (but it doesn't care unless one uses certain
presets).
Though, as Steven pointed out, ppm2raw is doing the scaling for you,
as well as some more chroma conversion and subsampling. Bleah.
Is "ppm2raw" the only way to generate DV?
Is there no YUV4MPEG2 --> DV utility?
If not, it is sorely missing --- because the unnecessary colorspace
conversions and resampling in the above pipeline are lossy:
4:2:2 Y'CbCr --> 4:2:0/jpeg Y'CbCr --> 4:4:4 RGB --> 4:2:0/paldv Y'CbCr
(Does qttoy4m produce 4:2:2 output, or is it converting to 4:2:0?
Hopefully, if the source file is 4:2:2, it leaves it at 4:2:2.
Is the source interlaced bottom-field-first?)
Anyhow, my suggestion to you for this instance is:
y4mscaler -O preset=DV -O chromass=444
This will give you DV frame-sizing, but 4:4:4 Y'CbCr chroma, so that
"y4mtoppm" won't have to do any chroma-supersampling itself. (Then,
"ppm2raw" will subsample back to 4:2:0.)
If the input is non-interlaced, you may need to override the input
detection with "-I ilace=BOTTOM_FIRST". If the frame rate is odd,
you may need to specify "-I norm=PAL" as well.
I'm curious if this works any better.
-matt m.
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