[1/1] gstreamer: Prefer non-raw (i.e. non-Bayer) formats in caps negotiation
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Message ID 20260702145317.86482-2-david.plowman@raspberrypi.com
State New
Headers show
Series
  • Make Gstreamer prefer non-raw caps
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Commit Message

David Plowman July 2, 2026, 2:39 p.m. UTC
Existing code was preferring fixed size outputs rather than ones with
ranges, resulting in raw output formats being preferred even when
applications ("cheese" is one such example) aren't expecting them and
subsequently fail.

The revised version looks at raw (in the Bayer sense) and non-raw
formats separately, preferring fixed size outputs within each
category, but then will opt for the non-raw formats if any were
available. This still allows applications that explicitly request raw
formats to get them.

Fixes, for example, "cheese" on Raspberry Pi.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
---
 src/gstreamer/gstlibcamera-utils.cpp | 96 +++++++++++++++++++++-------
 src/gstreamer/gstlibcamera-utils.h   |  2 +-
 src/gstreamer/gstlibcamerasrc.cpp    |  3 +-
 3 files changed, 75 insertions(+), 26 deletions(-)

Patch
diff mbox series

diff --git a/src/gstreamer/gstlibcamera-utils.cpp b/src/gstreamer/gstlibcamera-utils.cpp
index 6541d478..4f87525f 100644
--- a/src/gstreamer/gstlibcamera-utils.cpp
+++ b/src/gstreamer/gstlibcamera-utils.cpp
@@ -435,20 +435,54 @@  gst_libcamera_stream_configuration_to_caps(const StreamConfiguration &stream_cfg
 	return caps;
 }
 
-void gst_libcamera_configure_stream_from_caps(StreamConfiguration &stream_cfg,
+/*
+ * We will want to distinguish between caps structures corresponding to
+ * raw and non-raw (processed) output images, as this will help inform
+ * our choice of preferred format.
+ *
+ * We identify Bayer as being the principle "raw" format here, but note
+ * that we are considering greyscale to be raw too (e.g. a raw
+ * monochrome sensor).
+ */
+static bool
+gst_libcamera_structure_is_raw_capture(const GstStructure *s)
+{
+	if (gst_structure_has_name(s, "video/x-bayer"))
+		return true;
+
+	if (gst_structure_has_name(s, "video/x-raw")) {
+		const gchar *format = gst_structure_get_string(s, "format");
+
+		if (format && (!strcmp(format, "GRAY8") || !strcmp(format, "GRAY16_LE") ||
+			       !strcmp(format, "GRAY10_LE16")))
+			return true;
+	}
+
+	return false;
+}
+
+bool gst_libcamera_configure_stream_from_caps(StreamConfiguration &stream_cfg,
 					      GstCaps *caps, GstVideoTransferFunction *transfer)
 {
 	GstVideoFormat gst_format = pixel_format_to_gst_format(stream_cfg.pixelFormat);
 	guint i;
-	gint best_fixed = -1, best_in_range = -1;
 	GstStructure *s;
 
 	/*
-	 * These are delta weight computed from:
-	 *   ABS(width - stream_cfg.size.width) * ABS(height - stream_cfg.size.height)
+	 * Track the best size match (by delta weight, see below) separately
+	 * for raw sensor capture structures (Bayer/mono) and non-raw ones.
+	 * The previous logic that preferred fixed sizes over a range is
+	 * preserved within each of these "families".
 	 */
-	guint best_fixed_delta = G_MAXUINT;
-	guint best_in_range_delta = G_MAXUINT;
+	struct FormatMatch {
+		bool seen = false;
+		gint fixed = -1;
+		guint fixed_delta = G_MAXUINT;
+		gint in_range = -1;
+		guint in_range_delta = G_MAXUINT;
+
+		gint best() const { return fixed >= 0 ? fixed : in_range; }
+	} raw, non_raw;
 
 	/* First fixate the caps using default configuration value. */
 	g_assert(gst_caps_is_writable(caps));
@@ -458,38 +492,50 @@  void gst_libcamera_configure_stream_from_caps(StreamConfiguration &stream_cfg,
 		s = gst_caps_get_structure(caps, i);
 		gint width, height;
 		guint delta;
+		bool is_fixed = gst_structure_has_field_typed(s, "width", G_TYPE_INT) &&
+				gst_structure_has_field_typed(s, "height", G_TYPE_INT);
 
-		if (gst_structure_has_field_typed(s, "width", G_TYPE_INT) &&
-		    gst_structure_has_field_typed(s, "height", G_TYPE_INT)) {
+		if (is_fixed) {
 			gst_structure_get_int(s, "width", &width);
 			gst_structure_get_int(s, "height", &height);
-
-			delta = ABS(width - (gint)stream_cfg.size.width) * ABS(height - (gint)stream_cfg.size.height);
-
-			if (delta < best_fixed_delta) {
-				best_fixed_delta = delta;
-				best_fixed = i;
-			}
 		} else {
 			gst_structure_fixate_field_nearest_int(s, "width", stream_cfg.size.width);
 			gst_structure_fixate_field_nearest_int(s, "height", stream_cfg.size.height);
 			gst_structure_get_int(s, "width", &width);
 			gst_structure_get_int(s, "height", &height);
+		}
 
-			delta = ABS(width - (gint)stream_cfg.size.width) * ABS(height - (gint)stream_cfg.size.height);
+		delta = ABS(width - (gint)stream_cfg.size.width) * ABS(height - (gint)stream_cfg.size.height);
 
-			if (delta < best_in_range_delta) {
-				best_in_range_delta = delta;
-				best_in_range = i;
+		FormatMatch &match = gst_libcamera_structure_is_raw_capture(s) ? raw : non_raw;
+		match.seen = true;
+		if (is_fixed) {
+			if (delta < match.fixed_delta) {
+				match.fixed_delta = delta;
+				match.fixed = i;
 			}
+		} else if (delta < match.in_range_delta) {
+			match.in_range_delta = delta;
+			match.in_range = i;
 		}
 	}
 
-	/* Prefer reliable fixed value over ranges */
-	if (best_fixed >= 0)
-		s = gst_caps_get_structure(caps, best_fixed);
-	else
-		s = gst_caps_get_structure(caps, best_in_range);
+	/*
+	 * Raw foramts are likely to be useful only to applications that
+	 * specifically ask for them. Other applications will typically be
+	 * unable to handle them and fail. Therefore return a non-raw match
+	 * if we have one, falling back to raw formats if that's all that
+	 * was requested. Note how both raw and non-raw variants preserve
+	 * the previous "prefer fixed" behaviour in their own right.
+	 */
+	gint best = non_raw.best() >= 0 ? non_raw.best() : raw.best();
+
+	if (best < 0) {
+		GST_WARNING("Failed to find a suitable caps structure to configure the stream");
+		return false;
+	}
+
+	s = gst_caps_get_structure(caps, best);
 
 	if (gst_structure_has_name(s, "video/x-raw")) {
 		const gchar *format = gst_video_format_to_string(gst_format);
@@ -529,6 +575,8 @@  void gst_libcamera_configure_stream_from_caps(StreamConfiguration &stream_cfg,
 
 		stream_cfg.colorSpace = colorspace_from_colorimetry(colorimetry, transfer);
 	}
+
+	return true;
 }
 
 void gst_libcamera_get_framerate_from_caps(GstCaps *caps,
diff --git a/src/gstreamer/gstlibcamera-utils.h b/src/gstreamer/gstlibcamera-utils.h
index 35df56fb..5ce0e839 100644
--- a/src/gstreamer/gstlibcamera-utils.h
+++ b/src/gstreamer/gstlibcamera-utils.h
@@ -18,7 +18,7 @@ 
 GstCaps *gst_libcamera_stream_formats_to_caps(const libcamera::StreamFormats &formats);
 GstCaps *gst_libcamera_stream_configuration_to_caps(const libcamera::StreamConfiguration &stream_cfg,
 						    GstVideoTransferFunction transfer);
-void gst_libcamera_configure_stream_from_caps(libcamera::StreamConfiguration &stream_cfg,
+bool gst_libcamera_configure_stream_from_caps(libcamera::StreamConfiguration &stream_cfg,
 					      GstCaps *caps, GstVideoTransferFunction *transfer);
 void gst_libcamera_get_framerate_from_caps(GstCaps *caps, GstStructure *element_caps);
 void gst_libcamera_clamp_and_set_frameduration(libcamera::ControlList &controls,
diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
index 9061f916..66b31ce8 100644
--- a/src/gstreamer/gstlibcamerasrc.cpp
+++ b/src/gstreamer/gstlibcamerasrc.cpp
@@ -605,7 +605,8 @@  gst_libcamera_src_negotiate(GstLibcameraSrc *self)
 
 		/* Fixate caps and configure the stream. */
 		caps = gst_caps_make_writable(caps);
-		gst_libcamera_configure_stream_from_caps(stream_cfg, caps, &transfer[i]);
+		if (!gst_libcamera_configure_stream_from_caps(stream_cfg, caps, &transfer[i]))
+			return false;
 		gst_libcamera_get_framerate_from_caps(caps, element_caps);
 	}