Severe artifacts when decoding WMV / WMV3 (Windows Media Video 9) / VC-1 videos

[batou]

Summary of the bug:
I've noticed that new versions of mpv video player cannot play WMV videos reliably anymore. There are always visual artifacts every minute or so (keyframes maybe?).

Today I had some time and decided to investigate. Artifacting only occurs with VC-1 WMV videos (not older codecs). I've asked for help from mpv team but they sent me here since it's not an mpv issue.

Here's an example of artifacts: Left is ffmpeg-based player (mpv) and right is a player that doesn't use ffmpeg:

​https://i.imgur.com/jtHTe34.jpg

Usually, it's not as severe as this example but this bug makes WMV videos completely unwatchable in mpv.

Sample video: ​http://samples.mplayerhq.hu/V-codecs/WMV9/halo2_wmp9_WMV3+audio0x162.wmv

$ mpv --version
mpv 0.26.0-237-g5771f7abf4 (C) 2000-2017 mpv/MPlayer/mplayer2 projects
 built on Linux x86_64
ffmpeg library versions:
   libavutil       55.74.100
   libavcodec      57.105.100
   libavformat     57.81.100
   libswscale      4.7.103
   libavfilter     6.102.100
   libswresample   2.8.100
ffmpeg version: N-87204-gd8bc198d09

[batou]

image of artifacts

[Hendrik]

The issue seems to occur irregardless if software or hardware decoding is used, so that should limit where the bug occurs. Probably header parsing or reference management.

[Carl Eugen Hoyos]

I would have expected that hardware decoders do not support this kind of samples - do they?

[Hendrik]

Its ordinary WMV3 Main Profile, they should. (contrary to the OPs ticket description, its not VC-1, that would be Advanced Profile)

[Carl Eugen Hoyos]

I thought the sample contains old, partly unknown WMV3 from a time when there were no profiles, no?

[batou]

@cehoyos: I have no idea how old that WMV file is but I've been unable to play _any_ WMV3/VC-1 video with mpv recently. mpv produces visual errors on all of the files I tried even though other players play them fine. It only happens with VC-1/wmv3 files (other forms on .wmv don't produce visual artifacts with mpv). It's really annoying to have to use some other player.

[Carl Eugen Hoyos]

Fixed by Jerome Borsboom in b6402278322d1f64810cac4bea26d34d7b9a2e6a