Bug report : wmv_green_squares_wmp Subject : Transcoding grey static video to WMV causes green square artefacts in Windows Media Player I transcoded a simple GIF animation to WMV. Part of the picture displayed as green square artefacts during playback in Windows Media Player. I've extracted and expanded this part of the picture. It features grey pixels with somewhat high frequencies (noise). This new samples easily produces the problem in WMP. The same output is decoded fine with libavcodec and all players using it. Using Windows Media Encoder on the same input doesn't produce the problem. I also figured that filtering out the high frequencies would fix the problem. For example, using GStreamer's postproc_lowpass5 filter with scope=2 quality=0. ffmpeg -i grey.avi -vcodec wmv2 ffout.wmv FFmpeg version SVN-r9376, Copyright (c) 2000-2007 Fabrice Bellard, et al. configuration: --prefix=/opt/sherdev/MPlayer/1.0rc1 --enable-gpl --disable-strip --disable-mmx libavutil version: 49.4.0 libavcodec version: 51.40.4 libavformat version: 51.12.1 built on Jun 20 2007 14:58:35, gcc: 3.4.6 Input #0, avi, from 'grey.avi': Duration: 00:00:02.0, start: 0.000000, bitrate: 93 kb/s Stream #0.0: Video: rawvideo, yuv420p, 96x80, 1.00 fps(r) Output #0, asf, to 'ffout.wmv': Stream #0.0: Video: wmv2, yuv420p, 96x80, q=2-31, 200 kb/s, 1.00 fps(c) Stream mapping: Stream #0.0 -> #0.0 Compiler did not align stack variables. Libavcodec has been miscompiled and may be very slow or crash. This is not a bug in libavcodec, but in the compiler. Do not report crashes to FFmpeg developers. Press [q] to stop encoding frame= 2 fps= 0 q=2.0 Lsize= 4kB time=2.0 bitrate= 14.5kbits/s video:2kB audio:0kB global headers:0kB muxing overhead 120.742092% Note, for some reason, the output by ffmpeg doesn't play as is in WMP, I had to remux it by fixing timestamps using GStreamer. I provided both outputs for analysis. In either case, the container isn't the issue, it realy is the encoded stream. Files : grey.avi : the input sample ffout.wmv : the output from ffmpeg (doesn't play in WMP) greyout.wmv : passthrough remuxed output (plays in WMP) wmp_ss.jpg : screen shot of Windows Media Player depicting the problem report.txt : this bug report The remuxed output is produced using this pipeline : gst-launch-0.10 \ filesrc location=ffout.wmv ! \ asfdemux ! \ asfmux force-duration=10000 input-video-buffer-duration=2000 ! \ filesink location=greyout.wmv