video: make it possible to always override hardware decoding format

Mostly an obscure option for testing. But --videotoolbox-format can be
deprecated, as it becomes redundant.

We rely on the libavutil hwcontext implementation to reject invalid
pixfmts, or not to blow up if they are incompatible.

DOCS/interface-changes.rst

@@ -43,6 +43,8 @@ Interface changes
     - the --msg-level option now affects --log-file
     - drop "audio-out-detected-device" property - this was unavailable on all
       audio output drivers for quite a while (coreaudio used to provide it)
+    - deprecate --videotoolbox-format (use --hwdec-image-format, which affects
+      most other hwaccels)
  --- mpv 0.27.0 ---
     - drop previously deprecated --field-dominance option
     - drop previously deprecated "osd" command

DOCS/man/options.rst

@@ -835,6 +835,16 @@ Video
     The old alias ``--hwdec-preload`` has different behavior if the option value
     is ``no``.
 
+``--hwdec-image-format=<name>``
+    Set the internal pixel format used by hardware decoding via ``--hwdec``
+    (default ``no``). The special value ``no`` selects an implementation
+    specific standard format. Most decoder implementations support only one
+    format, and will fail to initialize if the format is not supported.
+
+    Some implementations might support multiple formats. In particular,
+    videotoolbox is known to require ``uyvy422`` for good performance on some
+    older hardware.
+
 ``--videotoolbox-format=<name>``
     Set the internal pixel format used by ``--hwdec=videotoolbox`` on OSX. The
     choice of the format can influence performance considerably. On the other
@@ -845,6 +855,9 @@ Video
     Since mpv 0.25.0, ``no`` is an accepted value, which lets the decoder pick
     the format on newer FFmpeg versions (will use ``nv12`` on older versions).
 
+    Deprecated. Use ``--hwdec-image-format`` if you really need this. If both
+    are specified, ``--hwdec-image-format`` wins.
+
 ``--panscan=<0.0-1.0>``
     Enables pan-and-scan functionality (cropping the sides of e.g. a 16:9
     video to make it fit a 4:3 display without black bands). The range

options/options.c

@@ -443,8 +443,10 @@ const m_option_t mp_opts[] = {
     OPT_CHOICE_C("hwdec", hwdec_api, 0, mp_hwdec_names),
     OPT_STRING("hwdec-codecs", hwdec_codecs, 0),
 #if HAVE_VIDEOTOOLBOX_HWACCEL
-    OPT_IMAGEFORMAT("videotoolbox-format", videotoolbox_format, 0, .min = -1),
+    OPT_IMAGEFORMAT("videotoolbox-format", videotoolbox_format, 0, .min = -1,
+                    .deprecation_message = "use --hwdec-image-format instead"),
 #endif
+    OPT_IMAGEFORMAT("hwdec-image-format", hwdec_image_format, 0, .min = -1),
 
     // -1 means auto aspect (prefer container size until aspect change)
     //  0 means square pixels

options/options.h

@@ -292,6 +292,7 @@ typedef struct MPOpts {
     int hwdec_api;
     char *hwdec_codecs;
     int videotoolbox_format;
+    int hwdec_image_format;
 
     int w32_priority;
 

video/decode/vd_lavc.c

@@ -807,6 +807,8 @@ static int init_generic_hwaccel(struct dec_video *vd)
 
     if (hwdec->image_format == IMGFMT_VIDEOTOOLBOX)
         av_sw_format = imgfmt2pixfmt(vd->opts->videotoolbox_format);
+    if (vd->opts->hwdec_image_format)
+        av_sw_format = imgfmt2pixfmt(vd->opts->hwdec_image_format);
 
     if (av_sw_format == AV_PIX_FMT_NONE) {
         MP_VERBOSE(ctx, "Unsupported hw decoding format: %s\n",