[gstreamer-bugs] [Bug 615471] Videoscale filter broken

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=615471
  GStreamer | gst-plugins-base | git

--- Comment #13 from David Schleef <ds at schleef.org> 2010-05-17 22:18:22 UTC ---
(In reply to comment #12)
> mpeg2dec detects progressive content already, it checks if the sequence header
> has the progressive flag.

This is a flag for interlaced encoding, not progressive content.  These are two
entirely separate concepts.  As an example, DVDs of films are almost always 24
fps progressive *content*, but are *encoded* interlaced at 50/60 fps. 
GStreamer passes around the encoding flag, not the content flag.  Whether or
not the content is interlaced or progressive can only be determined by
heuristics.  Some of the heuristic inputs are in the MPEG-2 bitstream (RFF
flag), some are guessed by analysing pictures.

The most effective and straightforward method of scaling interlaced content,
e.g., from 480i to 1080i, would be to deinterlace, scale reconstructed
full-size fields, then reinterlace.  Scaling progressive content that is
interlaced-coded is similar: inverse telecine, scale frames, then telecine.  Of
course, we don't have elements that do half of those operations, and the
inverse telecine element needs some work to be useful.  One could combine these
operations into a single element, but that seems like a step to be taken once
the functionality exists.

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