[FFmpeg-user] -vf tinterlace=6 not behaving as expected

[Andy Furniss]

I see a recent commit fixed some aspects of this and referred to some 
discussions outlining behavior.

http://git.videolan.org/gitweb.cgi/ffmpeg.git/?p=ffmpeg.git;a=commit;h=0d5ae023b2b7b860cbbfb7763f94da76bc841788

http://forum.xbmc.org/showthread.php?tid=81834

https://github.com/mpv-player/mpv/issues/624#issuecomment-37685195

also

https://www.ffmpeg.org/ffmpeg-filters.html#tinterlace

describes what the filter should do, the trouble is when I test it as below
with eg the scrolling letters burosch1.mpg (available in ffmpeg or 
mplayer samples IIRC).
I don't see what I expect when frame stepping the result in that both 
fields move each frame rather than one being the same.

The file does seem to have x2 frames and each frame has half the motion 
per step of the master, so I can only assume that the fields are getting 
swapped which is not the described behavior.

ffm -loglevel verbose -i burosch1.mpg -vf tinterlace=interlacex2 -an -sn 
-vcodec rawvideo out.nut
ffmpeg version N-61589-g37c07d4 Copyright (c) 2000-2014 the FFmpeg 
developers
   built on Mar 18 2014 21:32:47 with gcc 4.8.2 (GCC)
   configuration: --prefix=/usr --enable-gpl --enable-libmp3lame 
--enable-libx264 --enable-x11grab
   libavutil      52. 67.100 / 52. 67.100
   libavcodec     55. 52.102 / 55. 52.102
   libavformat    55. 34.101 / 55. 34.101
   libavdevice    55. 11.100 / 55. 11.100
   libavfilter     4.  3.100 /  4.  3.100
   libswscale      2.  5.101 /  2.  5.101
   libswresample   0. 18.100 /  0. 18.100
   libpostproc    52.  3.100 / 52.  3.100
Input #0, mpeg, from 'burosch1.mpg':
   Duration: 00:00:29.92, start: 0.500000, bitrate: 8051 kb/s
     Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv), 720x576 
[SAR 64:45 DAR 16:9], max. 8000 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
File 'out.nut' already exists. Overwrite ? [y/N] y
[graph 0 input from stream 0:0 @ 0x2ab4880] w:720 h:576 pixfmt:yuv420p 
tb:1/90000 fr:25/1 sar:64/45 sws_param:flags=2
[Parsed_tinterlace_0 @ 0x2ab42c0] mode:6 filter:off h:576 -> h:576
Output #0, nut, to 'out.nut':
   Metadata:
     encoder         : Lavf55.34.101
     Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 720x576 
[SAR 64:45 DAR 16:9], q=2-31, 200 kb/s, 51200 tbn, 50 tbc
Stream mapping:
   Stream #0:0 -> #0:0 (mpeg2video -> rawvideo)
Press [q] to stop, [?] for help
No more output streams to write to, finishing.=00:00:28.60 
bitrate=248844.0kbits/s
frame= 1498 fps=332 q=0.0 Lsize=  910086kB time=00:00:29.96 
bitrate=248846.0kbits/s
video:910035kB audio:0kB subtitle:0 data:0 global headers:0kB muxing 
overhead 0.005641%