[Mlt-devel] videostab2 interpolation bug

[Net K. <the...@gm...>]

Hi, I use melt (0.9) because of the videostab2 filter. Transcode is
practically unusable and there aren't any ffmpeg binaries available
yet with vid.stab enabled (as far as I know).

It is sad that the included version (0.75) is older than 3 years. The
developer was quite active in the meantime.

There is also an ugly bug in the melt version: it seems to ignore the
interpolation setting. The only way it gets reported (with -debug)
correctly, is to set "rescaler=name" for the consumer like:
melt -debug test.mlt -consumer avformat f=yuv4mpegpipe
rescale=bicublin | ffmpeg -i - image%02d.png

This outputs (along other lines):
Image Transformation/Stabilization Settings:
    smoothing = 10
    maxshift  = -1
    maxangle  = -1.000000
    crop      = Keep
    relative  = True
    invert    = False
    zoom      = 0.000000
    optzoom   = On
    interpol  = Bi-Cubic (4) <== OK!
    sharpen   = 0.800000
Final zoom: 0.000000

Corresponding code section:
https://github.com/mltframework/mlt/blob/2308a7/src/modules/videostab/filter_videostab2.c#L168

However, no matter what interpolation setting is used, the image
always looks uninterpolated. Here is a sample with default settings
and the vectors:
1=0/0:0.02x0;2=0/0:-0.01x0;3=0/0:-0.014x0;4=0/0:0.0265x0;5=0/0:0.0123x0;6=0/0:-0.0178x0;7=0/0:-0.02044x0;8=0/0:0.01276x0;9=0/0:0.01111x0
Frames: http://imgur.com/a/q3khB#0
Original: https://en.wikipedia.org/wiki/File:Pm5544_ntsc-1.png

The code looks right, though:
https://github.com/mltframework/mlt/blob/2308a7/src/modules/videostab/transform_image.c#L674

For a normal video, this results in wobbling blocks.

Can this be fixed?

Best,
Adrian