vabasedec: refactor format and capsfeature selection

This is a simplification of the venerable
gst_va_base_dec_get_preferred_format_and_caps_features() function, which
predates since gstreamer-vaapi. It's used to select the format and the
capsfeature to use when setting the output state. It was complex and hard to
follow. This refactor simplifies a lot the algorithm.

The first thing to remove _downstream_has_video_meta() since, most of the time
it will be called before the caps negotiation, and allocation queries make sense
only after caps negotiation. It might work during renegotiation but, in that
case, caps feature change is uncommon. Better a simple and common approach.

Also, for performance, instead of dealing with caps features as strings, GQuarks
are used.

The refactor works like this:

1. If peer pad returns any caps, the returned caps feature is system memory and
   looks for a proper format in the allowed caps.

2. The allowed caps are traversed at most 3 times: one per each valid caps
   feature. First VAMemory, later DMABuf, and last system memory. The first to
   match in allowed caps is picked, and the first format matching with the
   chroma is picked too.

Notice that, right now, using playbin videoconvert never return any.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6154>

subprojects/gst-plugins-bad/sys/va/gstvabasedec.c

@@ -744,168 +744,103 @@ gst_va_base_dec_class_init (GstVaBaseDecClass * klass, GstVaCodecs codec,
           G_PARAM_READABLE | G_PARAM_STATIC_STRINGS));
 }
 
-/* XXX: if chroma has not an available format, the first format is
+static inline GstVideoFormat
- * returned, relying on an hypothetical internal CSC */
+_get_video_format_from_value (const GValue * format, gboolean drm_format,
+    guint64 * modifier)
+{
+  guint32 fourcc;
+  const char *fmt;
+
+  g_assert (G_VALUE_HOLDS_STRING (format));
+
+  fmt = g_value_get_string (format);
+
+  if (drm_format) {
+    fourcc = gst_video_dma_drm_fourcc_from_string (fmt, modifier);
+    return gst_va_video_format_from_drm_fourcc (fourcc);
+  }
+
+  return gst_video_format_from_string (fmt);
+}
+
 static GstVideoFormat
 _find_video_format_from_chroma (const GValue * formats, guint chroma_type,
     gboolean drm_format, guint64 * modifier)
 {
-  GstVideoFormat fmt;
+  GstVideoFormat fmt = GST_VIDEO_FORMAT_UNKNOWN;
-  guint32 fourcc;
   guint i, num_values;
 
   if (!formats)
     return GST_VIDEO_FORMAT_UNKNOWN;
 
   if (G_VALUE_HOLDS_STRING (formats)) {
-    if (drm_format) {
+    fmt = _get_video_format_from_value (formats, drm_format, modifier);
-      fourcc = gst_video_dma_drm_fourcc_from_string
+    if (gst_va_chroma_from_video_format (fmt) == chroma_type)
-          (g_value_get_string (formats), modifier);
+      return fmt;
-      return gst_va_video_format_from_drm_fourcc (fourcc);
-    } else {
-      return gst_video_format_from_string (g_value_get_string (formats));
-    }
   } else if (GST_VALUE_HOLDS_LIST (formats)) {
-    GValue *val, *first_val = NULL;
+    const GValue *format;
 
     num_values = gst_value_list_get_size (formats);
     for (i = 0; i < num_values; i++) {
-      val = (GValue *) gst_value_list_get_value (formats, i);
+      format = gst_value_list_get_value (formats, i);
-      if (!val)
+      fmt = _get_video_format_from_value (format, drm_format, modifier);
-        continue;
-      if (!first_val)
-        first_val = val;
-
-      if (drm_format) {
-        fourcc = gst_video_dma_drm_fourcc_from_string (g_value_get_string (val),
-            modifier);
-        fmt = gst_va_video_format_from_drm_fourcc (fourcc);
-      } else {
-        fmt = gst_video_format_from_string (g_value_get_string (val));
-      }
 
       if (gst_va_chroma_from_video_format (fmt) == chroma_type)
         return fmt;
     }
-
-    if (first_val) {
-      if (drm_format) {
-        fourcc = gst_video_dma_drm_fourcc_from_string (g_value_get_string
-            (first_val), modifier);
-        return gst_va_video_format_from_drm_fourcc (fourcc);
-      } else {
-        return gst_video_format_from_string (g_value_get_string (first_val));
-      }
-    }
   }
 
   return GST_VIDEO_FORMAT_UNKNOWN;
 }
 
 static GstVideoFormat
-_caps_video_format_from_chroma (GstCaps * caps, GstCapsFeatures * features,
+_caps_video_format_from_chroma (GstCaps * caps, guint chroma_type)
-    guint chroma_type, guint64 * ret_modifier)
 {
   guint i, num_structures;
-  gboolean drm_format;
   GstCapsFeatures *feats;
   GstStructure *structure;
   const GValue *format;
-  GstVideoFormat fmt, ret_fmt = GST_VIDEO_FORMAT_UNKNOWN;
+  GstVideoFormat fmt;
-  guint64 modifier;
 
   num_structures = gst_caps_get_size (caps);
   for (i = 0; i < num_structures; i++) {
     feats = gst_caps_get_features (caps, i);
-    if (!gst_caps_features_is_equal (feats, features))
+    if (!gst_caps_features_is_equal (feats,
+            GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY))
       continue;
     structure = gst_caps_get_structure (caps, i);
-
-    if (gst_caps_features_contains (feats, GST_CAPS_FEATURE_MEMORY_DMABUF)) {
-      format = gst_structure_get_value (structure, "drm-format");
-      drm_format = TRUE;
-    } else {
     format = gst_structure_get_value (structure, "format");
-      drm_format = FALSE;
-    }
 
-    fmt = _find_video_format_from_chroma (format, chroma_type, drm_format,
+    fmt = _find_video_format_from_chroma (format, chroma_type, FALSE, NULL);
-        &modifier);
     if (fmt == GST_VIDEO_FORMAT_UNKNOWN)
       continue;
-
+    if (gst_va_chroma_from_video_format (fmt) == chroma_type)
-    if (ret_fmt == GST_VIDEO_FORMAT_UNKNOWN) {
+      return fmt;
-      ret_fmt = fmt;
-      if (ret_modifier)
-        *ret_modifier = modifier;
   }
 
-    if (gst_va_chroma_from_video_format (fmt) == chroma_type) {
+  return GST_VIDEO_FORMAT_UNKNOWN;
-      ret_fmt = fmt;
-      if (ret_modifier)
-        *ret_modifier = modifier;
-      break;
-    }
 }
 
-  return ret_fmt;
+/* ordered list of capsfeature preference */
-}
+enum
-
+{ VA, DMABUF, SYSMEM };
-static GstVideoFormat
-_default_video_format_from_chroma (GstVaBaseDec * base,
-    GstCaps * preferred_caps, GstCapsFeatures * features, guint chroma_type,
-    guint64 * modifier)
-{
-  GstCaps *tmpl_caps;
-  GstVideoFormat ret = GST_VIDEO_FORMAT_UNKNOWN;
-
-  tmpl_caps = gst_pad_get_pad_template_caps (GST_VIDEO_DECODER_SRC_PAD (base));
-
-  /* Make the preferred caps in the order of our template */
-  if (preferred_caps) {
-    GstCaps *tmp;
-    g_assert (!gst_caps_is_empty (preferred_caps));
-
-    tmp = tmpl_caps;
-    tmpl_caps = gst_caps_intersect_full (tmp, preferred_caps,
-        GST_CAPS_INTERSECT_FIRST);
-    gst_caps_unref (tmp);
-  }
-
-  ret = _caps_video_format_from_chroma (tmpl_caps, features, chroma_type,
-      modifier);
-
-  gst_caps_unref (tmpl_caps);
-
-  return ret;
-}
-
-/* Check whether the downstream supports VideoMeta; if not, we need to
- * fallback to the system memory. */
-static gboolean
-_downstream_has_video_meta (GstVaBaseDec * base, GstCaps * caps)
-{
-  GstQuery *query;
-  gboolean ret = FALSE;
-
-  query = gst_query_new_allocation (caps, FALSE);
-  if (gst_pad_peer_query (GST_VIDEO_DECODER_SRC_PAD (base), query))
-    ret = gst_query_find_allocation_meta (query, GST_VIDEO_META_API_TYPE, NULL);
-  gst_query_unref (query);
-
-  return ret;
-}
 
 void
 gst_va_base_dec_get_preferred_format_and_caps_features (GstVaBaseDec * base,
     GstVideoFormat * format, GstCapsFeatures ** capsfeatures,
     guint64 * modifier)
 {
-  GstCaps *peer_caps = NULL, *preferred_caps = NULL;
+  GstCaps *peer_caps, *allowed_caps;
   GstCapsFeatures *features;
-  GstStructure *structure;
+  guint num_structures, i, j;
-  guint num_structures, i;
   gboolean is_any;
+  /* array designators might not be supported by some compilers */
+  const GQuark feats[] = {
+    /* [VA] = */ g_quark_from_string (GST_CAPS_FEATURE_MEMORY_VA),
+    /* [DMABUF] = */ g_quark_from_string (GST_CAPS_FEATURE_MEMORY_DMABUF),
+    /* [SYSMEM] = */
+    g_quark_from_string (GST_CAPS_FEATURE_MEMORY_SYSTEM_MEMORY),
+  };
 
   g_return_if_fail (base);
 
@@ -917,70 +852,67 @@ gst_va_base_dec_get_preferred_format_and_caps_features (GstVaBaseDec * base,
     gst_clear_caps (&peer_caps);
   }
 
-  peer_caps = gst_pad_get_allowed_caps (GST_VIDEO_DECODER_SRC_PAD (base));
+  allowed_caps = gst_pad_get_allowed_caps (GST_VIDEO_DECODER_SRC_PAD (base));
-  GST_DEBUG_OBJECT (base, "Allowed caps %" GST_PTR_FORMAT, peer_caps);
+  GST_DEBUG_OBJECT (base, "Allowed caps %" GST_PTR_FORMAT, allowed_caps);
 
-  /* prefer memory:VASurface over other caps features */
+  /* if peer caps is any, returns format according memory to system caps in
-  num_structures = gst_caps_get_size (peer_caps);
+   * allowed caps
-  for (i = 0; i < num_structures; i++) {
+   *
-    features = gst_caps_get_features (peer_caps, i);
+   * if downstream doesn't support system memory negotiation will fail later.
-    structure = gst_caps_get_structure (peer_caps, i);
+   */
-
+  if (is_any) {
-    if (gst_caps_features_is_any (features))
+    features = GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY;
-      continue;
+    if (format)
-
+      *format = _caps_video_format_from_chroma (allowed_caps, base->rt_format);
-    if (gst_caps_features_contains (features, GST_CAPS_FEATURE_MEMORY_VA)) {
+    if (capsfeatures && *format != GST_VIDEO_FORMAT_UNKNOWN)
-      preferred_caps = gst_caps_new_full (gst_structure_copy (structure), NULL);
+      *capsfeatures = gst_caps_features_copy (features);
-      gst_caps_set_features_simple (preferred_caps,
-          gst_caps_features_copy (features));
-      break;
-    }
-  }
-
-  if (!preferred_caps)
-    preferred_caps = gst_caps_copy (peer_caps);
-
-  if (gst_caps_is_empty (preferred_caps)) {
-    if (capsfeatures)
-      *capsfeatures = NULL;     /* system memory */
-    if (format) {
-      *format = _default_video_format_from_chroma (base, NULL,
-          GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY, base->rt_format, NULL);
-    }
     goto bail;
   }
 
-  /* Use the first structure/feature is caps because is the
+  /* iterate allowed caps to find the first "capable" capability according our
-   * "preferred" one */
+   * ordered list of preferred caps features */
-  features = gst_caps_get_features (preferred_caps, 0);
+  num_structures = gst_caps_get_size (allowed_caps);
-  if (!features) {
+  for (i = 0; i < G_N_ELEMENTS (feats); i++) {
-    features = GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY;
+    for (j = 0; j < num_structures; j++) {
-  } else if (is_any
+      GstStructure *structure;
-      && !gst_caps_features_is_equal (features,
+      const GValue *formats;
-          GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY)
+      GstVideoFormat fmt;
-      && !_downstream_has_video_meta (base, preferred_caps)) {
+      guint64 mod = 0;
-    GST_INFO_OBJECT (base, "Downstream reports ANY caps but without"
-        " VideoMeta support; fallback to system memory.");
 
-    features = GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY;
+      features = gst_caps_get_features (allowed_caps, j);
-    gst_clear_caps (&preferred_caps);
+      if (!gst_caps_features_contains_id (features, feats[i]))
-    preferred_caps = gst_caps_copy (peer_caps);
+        continue;
-  }
 
+      structure = gst_caps_get_structure (allowed_caps, j);
+      if (i == DMABUF)
+        formats = gst_structure_get_value (structure, "drm-format");
+      else
+        formats = gst_structure_get_value (structure, "format");
 
+      fmt = _find_video_format_from_chroma (formats, base->rt_format,
+          i == DMABUF, &mod);
+
+      /* if doesn't found a proper format let's try other structure */
+      if (fmt == GST_VIDEO_FORMAT_UNKNOWN)
+        continue;
+
+      if (format)
+        *format = fmt;
+      if (i == DMABUF && modifier)
+        *modifier = mod;
       if (capsfeatures)
-    *capsfeatures = gst_caps_features_copy (features);
+        *capsfeatures = gst_caps_features_new_id (feats[i], NULL);
 
-  /* Use the format from chroma and available format for selected
+      goto bail;
-   * capsfeature */
-  if (format) {
-    *format = _default_video_format_from_chroma (base, preferred_caps,
-        features, base->rt_format, modifier);
     }
+  }
+
+  /* no matching format, let's fail */
+  if (i == G_N_ELEMENTS (feats))
+    *format = GST_VIDEO_FORMAT_UNKNOWN;
 
 bail:
-  gst_clear_caps (&preferred_caps);
+  gst_caps_unref (allowed_caps);
-  gst_clear_caps (&peer_caps);
 }
 
 static gboolean