image_writer: use common format selection for AVIF screenshots

--screenshot-avif-pixfmt no longer defaults to yuv420p.

DOCS/interface-changes.rst

@@ -31,6 +31,7 @@ Interface changes
     - add `--secondary-sub-delay`, decouple secondary subtitles from
       `--sub-delay`
     - add the `--osd-bar-border-size` option
+    - `--screenshot-avif-pixfmt` no longer defaults to yuv420p
  --- mpv 0.37.0 ---
     - `--save-position-on-quit` and its associated commands now store state files
       in %LOCALAPPDATA% instead of %APPDATA% directory by default on Windows.

DOCS/man/options.rst

@@ -4559,9 +4559,8 @@ Screenshot
     Default: ``libaom-av1``
 
 ``--screenshot-avif-pixfmt=<format>``
-    Specify the pixel format to the libavcodec encoder.
-
-    Default: ``yuv420p``
+    Specify the pixel format for the libavcodec encoder. Defaults to empty,
+    which lets mpv pick one close to the source format.
 
 ``--screenshot-avif-opts=key1=value1,key2=value2,...``
     Specifies libavcodec options for selected encoder. For more information,

video/image_writer.c

@@ -59,7 +59,6 @@ const struct image_writer_opts image_writer_opts_defaults = {
     .jxl_distance = 1.0,
     .jxl_effort = 4,
     .avif_encoder = "libaom-av1",
-    .avif_pixfmt = "yuv420p",
     .avif_opts = (char*[]){
         "usage",    "allintra",
         "crf",      "32",
@@ -717,7 +716,8 @@ bool write_image(struct mp_image *image, const struct image_writer_opts *opts,
 #if HAVE_AVIF_MUXER
     if (opts->format == AV_CODEC_ID_AV1) {
         write = write_avif;
-        destfmt = mp_imgfmt_from_name(bstr0(opts->avif_pixfmt));
+        if (opts->avif_pixfmt && opts->avif_pixfmt[0])
+            destfmt = mp_imgfmt_from_name(bstr0(opts->avif_pixfmt));
     }
 #endif
     if (opts->format == AV_CODEC_ID_WEBP && !opts->webp_lossless) {