Recently I accidentally found the following bug in Cinelerra-GG and created a patch to correct it. When trying to stabilize video with the 'Motion' plugin I got repeatedly a constantly accumulated clockwise rotation of the video frames (when tracking 'Previous frame same block') or twitching video (when 'Tracking single frame'). After some debugging and dumping temporary frames in PPM format I found that, for example, rotation of a frame to the angle of 0.000000 degrees actually results in its translation one pixel to the right and one pixel down. This was the reason for the Motion plugin to try constantly to rotate video about 0.25 degrees each frame. The actual location of this problem was in the Affine engine, namely in the used interpolation macros. The wrong expressions for displacements of the interpolated pixels lead to that, for example, that when the input and output points should coinside (which is the case for the 0 degree rotation), the X and Y of the pixel which are to be taken with the coefficient 1.0 become (tx-1,ty-1) instead of (tx,ty). Perhaps the bug in Affine could influence also other features in Cinelerra, but to observe such a subtle displacements in most of video editing scenarios looks not so easy. On the contrary, the accumulated rotation while motion stabilization makes it evident. In cinelerra/interp.h I corrected only the expressions for the integer coords and float displacements for the interpolated pixels. The main correction in cinelerra/affine.C (look in the patch attached) is at the lines 245-246: the processed frame block size was one pixel less both in horizontal and vertical directions. I have found only one other similar place in the code, namely in the 'Lens' plugin, and there the calculation of max x and y was correct. Additionally I'd propose to correct affine.C at the lines: 188 (perhaps an unportable method to compare a float variable with 0.0) 693 (looks like a definitely incorrect calculation of y1 for the package #0) The rest, commented out, are for debugging output only. This patch is against cin_5.1.20200430-src.tgz, I posted it to bugtracker as issue 479. Thanks for the attention Georgy _______________________________________________________________________________ Georgy Salnikov NMR Group Novosibirsk Institute of Organic Chemistry Lavrentjeva, 9, 630090 Novosibirsk, Russia Phone +7-383-3307864 Email [email protected] _______________________________________________________________________________