PSPunch wrote:
On 2016/04/08 5:04, Andy Furniss wrote:
Why do you need to make interlaced from progressive?
Excuse me to jump in. For example, when encoding for BD I need to
make the choice between 1080i to retain resolution, or 720p for ease
of handling. (Although I never had to used FFmpeg for this task)
I guess there are some valid cases.
720p is somewhat higher vertical res than 1080i allowing for two
fields and extra low pass filtering interlaced content undergoes.
If you have good reason (and 50/60 fps source) then you also have
to be careful around chroma conversions and any scaling filters for
which may get auto inserted and break chroma (cause it to bleed
between fields).
Is there a technical term for this phenomenon, or any resources I can
read further on this? Hopefully one aimed at video operators rather
than codec designers...
I don't really know the technical term, but mpeg mandates that 420
weaved interlaced and 420 progressive content have different chroma
sub-sampling positions. In the weaved case fields have to be treated
separately.
www.mir.com/DMG/chroma.html
I don't think ffmpeg can handle the positions for top/bottom correctly.
It can treat fields separately when scaling or changing chroma format.
-vf scale=interl=1 should do this, but sometimes depending on other
commands a scaler may be auto inserted which will mess this up.
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