On Tue, May 30, 2017 at 01:34:29PM -0400, Kevin Mark wrote: > Variables pertaining to the main video are now available when > using the scale2ref filter. This allows, as an example, scaling a > video with another as a reference point while maintaining the > original aspect ratio of the primary/non-reference video. > > Consider the following graph: scale2ref=iw/6:-1 [main][ref] > This will scale [main] to 1/6 the width of [ref] while maintaining > the aspect ratio. This works well when the AR of [ref] is equal to > the AR of [main] only. What the above filter really does is > maintain the AR of [ref] when scaling [main]. So in all non-same-AR > situations [main] will appear stretched or compressed to conform to > the same AR of the reference video. Without doing this calculation > externally there is no way to scale in reference to another input > while maintaining AR in libavfilter. > > To make this possible, we introduce eight new constants to be used > in the w and h expressions only in the scale2ref filter: > > * main_w/main_h: width/height of the main input video > * main_a: aspect ratio of the main input video > * main_sar: sample aspect ratio of the main input video > * main_dar: display aspect ratio of the main input video > * main_hsub/main_vsub: horiz/vert chroma subsample vals of main > * mdar: a shorthand alias of main_dar > > Of course, not all of these constants are needed for maintaining the > AR, but adding additional constants in line of what is available for > in/out allows for other scaling possibilities I have not imagined. > > So to now scale a video to 1/6 the size of another video using the > width and maintaining its own aspect ratio you can do this: > > scale2ref=iw/6:ow/mdar [main][ref] > > This is ideal for picture-in-picture configurations where you could > have a square or 4:3 video overlaid on a corner of a larger 16:9 > feed all while keeping the scaled video in the corner at its correct > aspect ratio and always the same size relative to the larger video. > > I've tried to re-use as much code as possible. I could not find a way > to avoid duplication of the var_names array. It must now be kept in > sync with the other (the normal one and the scale2ref one) for > everything to work which does not seem ideal. For every new variable > introduced/removed into/from the normal scale filter one must be > added/removed to/from the scale2ref version. Suggestions on how to > avoid var_names duplication are welcome. > > var_values has been increased to always be large enough for the > additional scale2ref variables. I do not forsee this being a problem > as the names variable will always be the correct size. From my > understanding of av_expr_parse_and_eval it will stop processing > variables when it runs out of names even though there may be > additional (potentially uninitialized) entries in the values array. > The ideal solution here would be using a variable-length array but > that is unsupported in C90. > > This patch does not remove any functionality and is strictly a > feature patch. There are no API changes. Behavior does not change for > any previously valid inputs. > > The applicable documentation has also been updated. > > Signed-off-by: Kevin Mark <kmark...@gmail.com> > --- > doc/filters.texi | 26 ++++++++++++++++++- > libavfilter/scale.c | 72 > ++++++++++++++++++++++++++++++++++++++++++++++++++--- > 2 files changed, 93 insertions(+), 5 deletions(-)
applied can you add a fate test that uses the new identifers ? Thanks [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Opposition brings concord. Out of discord comes the fairest harmony. -- Heraclitus
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