player: add track-list/N/image sub-property

This exposes whether a video track is detected as an image. This is
useful for profile conditions, property expansion and lavfi-complex, and
is more accurate than any detection even Lua scripts can perform, since
they can't differentiate between images and videos without container-fps
and audio and with duration 1 (which is the duration set by the mf
demuxer with the default --mf-fps=1).

The lavf demuxer image check is moved to where the number of frames is
available for comparison, and is modified to check the number of frames
and duration instead of the video codec. This doesn't misdetect videos
in a codec commonly used for images (e.g. mjpeg) as images, and can
detect images in a codec commonly used for videos (e.g. 1-frame gifs).

pix files are also now detected as images, while before they weren't
since the condition was checking if the AVInputFormat name ends with
_pipe, and alias_pix doesn't.

Both nb_frames and codec_info_nb_frames are checked because nb_frames is
0 for some video codecs (hevc, av1, vc1, mpeg1video, vp9 if forcing
--demuxer=lavf), and codec_info_nb_frames is 1 for others (mpeg, mpeg4,
wmv3).

The duration is checked as well because for some uncommon codecs and
containers found in FFMpeg's FATE suite, libavformat returns nb_frames =
0 and codec_info_nb_frames = 1. For some of them it even returns
duration = 0, so they are blacklisted in order to never be considered
images.

The extra codecs that would have to be blacklisted without checking the
duration are AV_CODEC_ID_4XM, AV_CODEC_ID_BINKVIDEO,
AV_CODEC_ID_DSICINVIDEO, AV_CODEC_ID_ESCAPE130, AV_CODEC_ID_MMVIDEO,
AV_CODEC_ID_NUV, AV_CODEC_ID_RL2, AV_CODEC_ID_SMACKVIDEO and
AV_CODEC_ID_XAN_WC3, while the containers are film-cpk, ivf and ogg.

The lower limit for duration is 10 because that's the duration of
1-frame gifs.

Streams with codec_info_nb_frames 0 are not considered images because
vp9 and av1 have nb_frames = 0 and codec_info_nb_frames = 0, and we
can't rely on just the duration to detect them because they could be
livestreams without an initial duration, and actually even if we could
for these codecs libavformat returns huge negative durations like
-9223372036854775808.

Some more images in the FATE suite that are really frames cut from a
video in an uncommon codec and container, like cine/bayer_gbrg8.cine,
could be detected by allowing codec_info_nb_frames = 0, but then any
present and future video codec with nb_frames = 0 and
codec_info_nb_frames = 0 would need to be added to the blacklist. Some
even have duration > 10, so to detect these images the duration check
would have to be removed, and all the previously mentioned extra codecs
and containers would have to be added added to the blacklists, which
means that images that use them (if they exist anywhere) will never be
detected. These FATE images aren't detected as such by mediainfo either
anyway, nor can a Lua script reliably detect them as images since they
have container-fps and duration > 0 and != 1, and you probably will
never see files like them anywhere else.

For attached pictures the lavf demuxer always set image to true, which
is necessary because they have duration > 10. There is a minor change in
behavior for which audio with attached pictures now has mf-fps as
container-fps instead of unavailable, but this makes it consistent with
external cover art, which was already being assigned mf-fps.

When the lavf demuxer fails, the mf one guesses if the file is an image
by its extension, so sh->image is set to true when the mf demuxer
succeds and there's only one file.

Even if you add a video's file type to --mf-type and open it with the mf
protocol, only the first frame is used, so setting image to true is
still accurate.

When converting an image to the extensions listed in demux/demux_mf.c,
tga and pam files are currently the only ones detected by the mf demuxer
rather than lavf. Actually they are detected with the image2 format, but
it is blacklisted; see d0fee0ac33a.

The mkv demuxer just sets image to true for any attached picture.

The timeline demuxer just copies the value of image from source to
destination. This sets image to true for attached pictures, standalone
images and images added with !new_stream in EDL playlists, but it is
imperfect since you could concatenate multiple images in an EDL playlist
(which should be done with the mf demuxer anyway). This is good enough
anyway since the comment of the modified function already says it is
"Imperfect and arbitrary".

2 files changed, 8 insertions, 4 deletions

diff --git a/DOCS/interface-changes.rst b/DOCS/interface-changes.rst
index ee84bc8f1c..d5b986aa2d 100644
--- a/DOCS/interface-changes.rst
+++ b/DOCS/interface-changes.rst
@@ -43,6 +43,7 @@ Interface changes
     - add a `--watch-later-options` option to allow configuring which
       options quit-watch-later saves
     - make `current-window-scale` writeable and use it in the default input.conf
+    - add ``track-list/N/image`` sub-property
  --- mpv 0.33.0 ---
     - add `--d3d11-exclusive-fs` flag to enable D3D11 exclusive fullscreen mode
       when the player enters fullscreen.
diff --git a/DOCS/man/input.rst b/DOCS/man/input.rst
index cd360d600b..5f9a5230af 100644
--- a/DOCS/man/input.rst
+++ b/DOCS/man/input.rst
@@ -2838,11 +2838,13 @@ Property list
     ``track-list/N/lang``
         Track language as identified by the file. Not always available.
 
-    ``track-list/N/albumart``
+    ``track-list/N/image``
         ``yes``/true if this is a video track that consists of a single
-        picture, ``no``/false or unavailable otherwise. This is used for video
-        tracks that are really images embedded in audio files and for external
-        cover art.
+        picture, ``no``/false or unavailable otherwise.
+
+    ``track-list/N/albumart``
+        ``yes``/true if this is an image embedded in an audio file or external
+        cover art, ``no``/false or unavailable otherwise.
 
     ``track-list/N/default``
         ``yes``/true if the track has the default flag set in the file,
@@ -2936,6 +2938,7 @@ Property list
                 "src-id"            MPV_FORMAT_INT64
                 "title"             MPV_FORMAT_STRING
                 "lang"              MPV_FORMAT_STRING
+                "image"             MPV_FORMAT_FLAG
                 "albumart"          MPV_FORMAT_FLAG
                 "default"           MPV_FORMAT_FLAG
                 "forced"            MPV_FORMAT_FLAG