gl: Add glviewconvert, glstereomix and glstereosplit elements

Conversion elements for transforming multiview/stereoscopic video

https://bugzilla.gnome.org/show_bug.cgi?id=611157

1 files changed, 702 insertions, 0 deletions

diff --git a/ext/gl/gstglstereomix.c b/ext/gl/gstglstereomix.c
new file mode 100644
index 000000000..1422823f7
--- /dev/null
+++ b/ext/gl/gstglstereomix.c
@@ -0,0 +1,702 @@
+/*
+ * Combine video streams to 3D stereo
+ *
+ * GStreamer
+ * Copyright (C) 2009 Julien Isorce <julien.isorce@gmail.com>
+ * Copyright (C) 2014 Jan Schmidt <jan@noraisin.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "gstglstereomix.h"
+
+#define GST_CAT_DEFAULT gst_gl_stereo_mix_debug
+GST_DEBUG_CATEGORY (gst_gl_stereo_mix_debug);
+
+#define gst_gl_stereo_mix_parent_class parent_class
+G_DEFINE_TYPE (GstGLStereoMix, gst_gl_stereo_mix, GST_TYPE_GL_MIXER);
+
+static GstCaps *_update_caps (GstVideoAggregator * vagg, GstCaps * caps);
+static gboolean _negotiated_caps (GstVideoAggregator * videoaggregator,
+    GstCaps * caps);
+gboolean gst_gl_stereo_mix_make_output (GstGLStereoMix * mix);
+static gboolean gst_gl_stereo_mix_process_frames (GstGLStereoMix * mixer,
+    GPtrArray * in_frames);
+
+#define DEFAULT_DOWNMIX GST_GL_STEREO_DOWNMIX_ANAGLYPH_GREEN_MAGENTA_DUBOIS
+
+/* GLStereoMix signals and args */
+enum
+{
+  /* FILL ME */
+  LAST_SIGNAL
+};
+
+enum
+{
+  PROP_0,
+  PROP_DOWNMIX_MODE
+};
+
+static GstStaticPadTemplate src_factory = GST_STATIC_PAD_TEMPLATE ("src",
+    GST_PAD_SRC,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS (GST_VIDEO_CAPS_MAKE_WITH_FEATURES
+        (GST_CAPS_FEATURE_MEMORY_GL_MEMORY,
+            "RGBA") "; "
+        GST_VIDEO_CAPS_MAKE_WITH_FEATURES
+        (GST_CAPS_FEATURE_META_GST_VIDEO_GL_TEXTURE_UPLOAD_META,
+            "RGBA")
+        "; " GST_VIDEO_CAPS_MAKE (GST_GL_COLOR_CONVERT_FORMATS))
+    );
+
+static GstStaticPadTemplate sink_factory = GST_STATIC_PAD_TEMPLATE ("sink_%u",
+    GST_PAD_SINK,
+    GST_PAD_REQUEST,
+    GST_STATIC_CAPS (GST_VIDEO_CAPS_MAKE_WITH_FEATURES
+        (GST_CAPS_FEATURE_MEMORY_GL_MEMORY,
+            "RGBA") "; "
+        GST_VIDEO_CAPS_MAKE_WITH_FEATURES
+        (GST_CAPS_FEATURE_META_GST_VIDEO_GL_TEXTURE_UPLOAD_META,
+            "RGBA")
+        "; " GST_VIDEO_CAPS_MAKE (GST_GL_COLOR_CONVERT_FORMATS))
+    );
+
+static GstFlowReturn gst_gl_stereo_mix_get_output_buffer (GstVideoAggregator *
+    videoaggregator, GstBuffer ** outbuf);
+static gboolean gst_gl_stereo_mix_stop (GstAggregator * agg);
+static gboolean gst_gl_stereo_mix_start (GstAggregator * agg);
+static gboolean gst_gl_stereo_mix_src_query (GstAggregator * agg,
+    GstQuery * query);
+
+static void
+gst_gl_stereo_mix_find_best_format (GstVideoAggregator * vagg,
+    GstCaps * downstream_caps, GstVideoInfo * best_info,
+    gboolean * at_least_one_alpha);
+
+static void gst_gl_stereo_mix_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec);
+static void gst_gl_stereo_mix_get_property (GObject * object, guint prop_id,
+    GValue * value, GParamSpec * pspec);
+
+static void gst_gl_stereo_mix_finalize (GObject * object);
+
+static GstFlowReturn
+gst_gl_stereo_mix_aggregate_frames (GstVideoAggregator * vagg,
+    GstBuffer * outbuffer);
+
+static void
+gst_gl_stereo_mix_class_init (GstGLStereoMixClass * klass)
+{
+  GObjectClass *gobject_class = (GObjectClass *) klass;
+  GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
+  GstVideoAggregatorClass *videoaggregator_class =
+      (GstVideoAggregatorClass *) klass;
+  GstAggregatorClass *agg_class = (GstAggregatorClass *) klass;
+  GstGLBaseMixerClass *base_mix_class = (GstGLBaseMixerClass *) klass;
+
+  GST_DEBUG_CATEGORY_INIT (GST_CAT_DEFAULT, "glstereomixer", 0,
+      "opengl stereoscopic mixer");
+
+  gobject_class->finalize = GST_DEBUG_FUNCPTR (gst_gl_stereo_mix_finalize);
+
+  gobject_class->get_property = gst_gl_stereo_mix_get_property;
+  gobject_class->set_property = gst_gl_stereo_mix_set_property;
+
+  gst_element_class_set_metadata (element_class, "OpenGL stereo video combiner",
+      "Filter/Effect/Video", "OpenGL stereo video combiner",
+      "Jan Schmidt <jan@centricular.com>");
+
+  g_object_class_install_property (gobject_class, PROP_DOWNMIX_MODE,
+      g_param_spec_enum ("downmix-mode", "Mode for mono downmixed output",
+          "Output anaglyph type to generate when downmixing to mono",
+          GST_TYPE_GL_STEREO_DOWNMIX_MODE_TYPE, DEFAULT_DOWNMIX,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
+  gst_element_class_add_pad_template (element_class,
+      gst_static_pad_template_get (&src_factory));
+  gst_element_class_add_pad_template (element_class,
+      gst_static_pad_template_get (&sink_factory));
+
+  agg_class->stop = gst_gl_stereo_mix_stop;
+  agg_class->start = gst_gl_stereo_mix_start;
+  agg_class->src_query = gst_gl_stereo_mix_src_query;
+
+  videoaggregator_class->aggregate_frames = gst_gl_stereo_mix_aggregate_frames;
+  videoaggregator_class->update_caps = _update_caps;
+  videoaggregator_class->negotiated_caps = _negotiated_caps;
+  videoaggregator_class->get_output_buffer =
+      gst_gl_stereo_mix_get_output_buffer;
+  videoaggregator_class->find_best_format = gst_gl_stereo_mix_find_best_format;
+  videoaggregator_class->preserve_update_caps_result = TRUE;
+
+  base_mix_class->supported_gl_api = GST_GL_API_OPENGL | GST_GL_API_OPENGL3;
+}
+
+static void
+gst_gl_stereo_mix_init (GstGLStereoMix * mix)
+{
+}
+
+static void
+gst_gl_stereo_mix_finalize (GObject * object)
+{
+  //GstGLStereoMix *mix = GST_GL_STEREO_MIX (object);
+
+  G_OBJECT_CLASS (parent_class)->finalize (object);
+}
+
+static gboolean
+gst_gl_stereo_mix_query_caps (GstPad * pad, GstAggregator * agg,
+    GstQuery * query)
+{
+  GstCaps *filter, *caps;
+
+  gst_query_parse_caps (query, &filter);
+
+  caps = gst_pad_get_current_caps (agg->srcpad);
+  if (caps == NULL) {
+    caps = gst_pad_get_pad_template_caps (agg->srcpad);
+  }
+
+  if (filter)
+    caps = gst_caps_intersect_full (filter, caps, GST_CAPS_INTERSECT_FIRST);
+
+  gst_query_set_caps_result (query, caps);
+  gst_caps_unref (caps);
+
+  return TRUE;
+}
+
+static gboolean
+gst_gl_stereo_mix_src_query (GstAggregator * agg, GstQuery * query)
+{
+  switch (GST_QUERY_TYPE (query)) {
+    case GST_QUERY_CAPS:
+      return gst_gl_stereo_mix_query_caps (agg->srcpad, agg, query);
+      break;
+    default:
+      break;
+  }
+
+  return GST_AGGREGATOR_CLASS (parent_class)->src_query (agg, query);
+}
+
+
+static GstFlowReturn
+gst_gl_stereo_mix_get_output_buffer (GstVideoAggregator * videoaggregator,
+    GstBuffer ** outbuf)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (videoaggregator);
+  GstFlowReturn ret = GST_FLOW_OK;
+
+#if 0
+
+  if (!mix->priv->pool_active) {
+    if (!gst_buffer_pool_set_active (mix->priv->pool, TRUE)) {
+      GST_ELEMENT_ERROR (mix, RESOURCE, SETTINGS,
+          ("failed to activate bufferpool"), ("failed to activate bufferpool"));
+      return GST_FLOW_ERROR;
+    }
+    mix->priv->pool_active = TRUE;
+  }
+
+  return gst_buffer_pool_acquire_buffer (mix->priv->pool, outbuf, NULL);
+#endif
+
+  if (!gst_gl_stereo_mix_make_output (mix)) {
+    gst_buffer_replace (&mix->primary_out, NULL);
+    gst_buffer_replace (&mix->auxilliary_out, NULL);
+    GST_ELEMENT_ERROR (mix, RESOURCE, SETTINGS,
+        ("Failed to generate output"), ("failed to generate output"));
+    ret = GST_FLOW_ERROR;
+  }
+
+  if (mix->auxilliary_out) {
+    *outbuf = mix->auxilliary_out;
+    mix->auxilliary_out = NULL;
+  } else {
+    *outbuf = mix->primary_out;
+    mix->primary_out = NULL;
+  }
+  return ret;
+}
+
+gboolean
+gst_gl_stereo_mix_make_output (GstGLStereoMix * mix)
+{
+  guint i;
+  GList *walk;
+  gboolean res = FALSE;
+  guint array_index = 0;
+  GstElement *element = GST_ELEMENT (mix);
+  gboolean missing_buffer = FALSE;
+
+  GST_LOG_OBJECT (mix, "Processing buffers");
+
+  GST_OBJECT_LOCK (mix);
+  walk = element->sinkpads;
+
+  i = mix->frames->len;
+  g_ptr_array_set_size (mix->frames, element->numsinkpads);
+  for (; i < element->numsinkpads; i++)
+    mix->frames->pdata[i] = g_slice_new0 (GstGLStereoMixFrameData);
+  while (walk) {
+    GstGLMixerPad *pad = GST_GL_MIXER_PAD (walk->data);
+    GstVideoAggregatorPad *vaggpad = walk->data;
+    GstGLStereoMixFrameData *frame;
+
+    GST_LOG_OBJECT (mix, "Checking pad %" GST_PTR_FORMAT, vaggpad);
+
+    frame = g_ptr_array_index (mix->frames, array_index);
+    frame->base.pad = pad;
+    frame->buf = NULL;
+
+    walk = g_list_next (walk);
+
+    if (vaggpad->buffer != NULL) {
+      frame->buf = vaggpad->buffer;
+
+      GST_DEBUG_OBJECT (pad, "Got buffer %" GST_PTR_FORMAT, frame->buf);
+    } else {
+      GST_LOG_OBJECT (mix, "No buffer on pad %" GST_PTR_FORMAT, vaggpad);
+      missing_buffer = TRUE;
+    }
+    ++array_index;
+  }
+  if (missing_buffer) {
+    /* We're still waiting for a buffer to turn up on at least one input */
+    GST_WARNING_OBJECT (mix, "Not generating output - need more input buffers");
+    res = TRUE;
+    goto out;
+  }
+
+  /* Copy GL memory from each input frame to the output */
+  if (!gst_gl_stereo_mix_process_frames (mix, mix->frames)) {
+    GST_LOG_OBJECT (mix, "Failed to process frames to output");
+    goto out;
+  }
+
+  if (mix->primary_out == NULL)
+    goto out;
+
+  res = TRUE;
+
+out:
+  GST_OBJECT_UNLOCK (mix);
+
+  return res;
+}
+
+static GstFlowReturn
+gst_gl_stereo_mix_aggregate_frames (GstVideoAggregator * vagg,
+    GstBuffer * outbuf)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (vagg);
+  /* If we're operating in frame-by-frame mode, push
+   * the primary view now, and let the parent class
+   * push the remaining auxilliary view */
+  if (GST_VIDEO_INFO_MULTIVIEW_MODE (&vagg->info) ==
+      GST_VIDEO_MULTIVIEW_MODE_FRAME_BY_FRAME) {
+    /* Transfer the timestamps video-agg put on the aux buffer */
+    gst_buffer_copy_into (mix->primary_out, outbuf,
+        GST_BUFFER_COPY_TIMESTAMPS, 0, -1);
+    gst_aggregator_finish_buffer (GST_AGGREGATOR (vagg), mix->primary_out);
+    mix->primary_out = NULL;
+
+    /* And actually, we don't want timestamps on the aux buffer */
+    GST_BUFFER_TIMESTAMP (outbuf) = GST_CLOCK_TIME_NONE;
+    GST_BUFFER_DURATION (outbuf) = GST_CLOCK_TIME_NONE;
+  }
+  return GST_FLOW_OK;
+}
+
+static void
+gst_gl_stereo_mix_get_property (GObject * object,
+    guint prop_id, GValue * value, GParamSpec * pspec)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (object);
+
+  switch (prop_id) {
+    case PROP_DOWNMIX_MODE:
+      g_value_set_enum (value, mix->downmix_mode);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+gst_gl_stereo_mix_set_property (GObject * object,
+    guint prop_id, const GValue * value, GParamSpec * pspec)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (object);
+
+  switch (prop_id) {
+    case PROP_DOWNMIX_MODE:
+      mix->downmix_mode = g_value_get_enum (value);
+      if (mix->viewconvert)
+        g_object_set_property (G_OBJECT (mix->viewconvert), "downmix-mode",
+            value);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+_free_glmixer_frame_data (GstGLStereoMixFrameData * frame)
+{
+  if (frame == NULL)
+    return;
+  if (frame->buf)
+    gst_buffer_unref (frame->buf);
+  g_slice_free1 (sizeof (GstGLStereoMixFrameData), frame);
+}
+
+static gboolean
+gst_gl_stereo_mix_start (GstAggregator * agg)
+{
+  guint i;
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (agg);
+  GstElement *element = GST_ELEMENT (agg);
+
+  if (!GST_AGGREGATOR_CLASS (parent_class)->start (agg))
+    return FALSE;
+
+  GST_OBJECT_LOCK (mix);
+  mix->array_buffers = g_ptr_array_new_full (element->numsinkpads,
+      (GDestroyNotify) _free_glmixer_frame_data);
+  mix->frames = g_ptr_array_new_full (element->numsinkpads, NULL);
+
+  g_ptr_array_set_size (mix->array_buffers, element->numsinkpads);
+  g_ptr_array_set_size (mix->frames, element->numsinkpads);
+
+  for (i = 0; i < element->numsinkpads; i++)
+    mix->frames->pdata[i] = g_slice_new0 (GstGLStereoMixFrameData);
+
+  mix->viewconvert = gst_gl_view_convert_new ();
+  g_object_set (G_OBJECT (mix->viewconvert), "downmix-mode",
+      mix->downmix_mode, NULL);
+
+  GST_OBJECT_UNLOCK (mix);
+
+  return TRUE;
+}
+
+static gboolean
+gst_gl_stereo_mix_stop (GstAggregator * agg)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (agg);
+
+  if (!GST_AGGREGATOR_CLASS (parent_class)->stop (agg))
+    return FALSE;
+
+  GST_OBJECT_LOCK (agg);
+  g_ptr_array_free (mix->frames, TRUE);
+  mix->frames = NULL;
+  g_ptr_array_free (mix->array_buffers, TRUE);
+  mix->array_buffers = NULL;
+  GST_OBJECT_UNLOCK (agg);
+
+  if (mix->viewconvert) {
+    gst_object_unref (mix->viewconvert);
+    mix->viewconvert = NULL;
+  }
+
+  return TRUE;
+}
+
+/* Convert to caps that can be accepted by this element... */
+static GstCaps *
+get_converted_caps (GstGLStereoMix * mix, GstCaps * caps)
+{
+#if 0
+  GstGLContext *context = GST_GL_BASE_MIXER (mix)->context;
+  GstCaps *result, *tmp;
+
+  GST_LOG_OBJECT (mix, "Converting caps %" GST_PTR_FORMAT, caps);
+  result = gst_gl_upload_transform_caps (context, GST_PAD_SINK, caps, NULL);
+  tmp = result;
+  GST_TRACE_OBJECT (mix, "transfer returned caps %" GST_PTR_FORMAT, tmp);
+
+  result =
+      gst_gl_color_convert_transform_caps (context, GST_PAD_SINK, tmp, NULL);
+  gst_caps_unref (tmp);
+  GST_TRACE_OBJECT (mix, "convert returned caps %" GST_PTR_FORMAT, tmp);
+
+  tmp = result;
+  result = gst_gl_view_convert_transform_caps (mix->viewconvert,
+      GST_PAD_SINK, tmp, NULL);
+  gst_caps_unref (tmp);
+#else
+  GstCaps *result;
+
+  GST_LOG_OBJECT (mix, "Converting caps %" GST_PTR_FORMAT, caps);
+  result = gst_gl_view_convert_transform_caps (mix->viewconvert,
+      GST_PAD_SINK, caps, NULL);
+#endif
+
+  GST_LOG_OBJECT (mix, "returning caps %" GST_PTR_FORMAT, result);
+
+  return result;
+}
+
+/* Return the possible output caps we decided in find_best_format() */
+static GstCaps *
+_update_caps (GstVideoAggregator * vagg, GstCaps * caps)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (vagg);
+
+  return gst_caps_ref (mix->out_caps);
+}
+
+/* Called after videoaggregator fixates our caps */
+static gboolean
+_negotiated_caps (GstVideoAggregator * vagg, GstCaps * caps)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (vagg);
+
+  GST_LOG_OBJECT (mix, "Configured output caps %" GST_PTR_FORMAT, caps);
+
+  if (GST_VIDEO_AGGREGATOR_CLASS (parent_class)->negotiated_caps)
+    if (!GST_VIDEO_AGGREGATOR_CLASS (parent_class)->negotiated_caps (vagg,
+            caps))
+      return FALSE;
+
+  /* Update the glview_convert output */
+  if (!gst_video_info_from_caps (&mix->out_info, caps))
+    return FALSE;
+
+  /* We can configure the view_converter now */
+  gst_gl_view_convert_set_context (mix->viewconvert,
+      GST_GL_BASE_MIXER (mix)->context);
+  gst_gl_view_convert_set_format (mix->viewconvert, &mix->mix_info,
+      &mix->out_info);
+
+  return TRUE;
+
+}
+
+static gboolean
+gst_gl_stereo_mix_process_frames (GstGLStereoMix * mixer, GPtrArray * frames)
+{
+  GstVideoAggregator *vagg = GST_VIDEO_AGGREGATOR (mixer);
+  GstBuffer *converted_buffer, *inbuf;
+  GstVideoInfo *out_info = &vagg->info;
+  gint count = 0, n;
+  gint v, views;
+  gint valid_views = 0;
+
+  inbuf = gst_buffer_new ();
+  while (count < frames->len) {
+    GstGLStereoMixFrameData *frame;
+    GstMemory *in_mem;
+
+    frame = g_ptr_array_index (frames, count);
+    GST_LOG_OBJECT (mixer, "Handling frame %d", count);
+
+    if (!frame) {
+      GST_DEBUG ("skipping texture, null frame");
+      count++;
+      continue;
+    }
+
+    in_mem = gst_buffer_get_memory (frame->buf, 0);
+
+    GST_LOG_OBJECT (mixer,
+        "Appending memory %" GST_PTR_FORMAT " to intermediate buffer", in_mem);
+    /* Appending the memory to a 2nd buffer locks it
+     * exclusive a 2nd time, which will mark it for
+     * copy-on-write. The ref will keep the memory
+     * alive but we add a parent_buffer_meta to also
+     * prevent the input buffer from returning to any buffer
+     * pool it might belong to
+     */
+    gst_buffer_append_memory (inbuf, in_mem);
+    /* Use parent buffer meta to keep input buffer alive */
+    gst_buffer_add_parent_buffer_meta (inbuf, frame->buf);
+
+    count++;
+    valid_views++;
+  }
+
+  if (mixer->mix_info.views != valid_views) {
+    GST_WARNING_OBJECT (mixer, "Not enough input views to process");
+    return FALSE;
+  }
+
+  if (GST_VIDEO_INFO_MULTIVIEW_MODE (out_info) ==
+      GST_VIDEO_MULTIVIEW_MODE_SEPARATED)
+    views = out_info->views;
+  else
+    views = 1;
+
+  if (gst_gl_view_convert_submit_input_buffer (mixer->viewconvert,
+          FALSE, inbuf) != GST_FLOW_OK)
+    return FALSE;
+
+  /* Clear any existing buffers, just in case */
+  gst_buffer_replace (&mixer->primary_out, NULL);
+  gst_buffer_replace (&mixer->auxilliary_out, NULL);
+
+  if (gst_gl_view_convert_get_output (mixer->viewconvert,
+          &mixer->primary_out) != GST_FLOW_OK)
+    return FALSE;
+
+  if (GST_VIDEO_INFO_MULTIVIEW_MODE (out_info) ==
+      GST_VIDEO_MULTIVIEW_MODE_FRAME_BY_FRAME) {
+    if (gst_gl_view_convert_get_output (mixer->viewconvert,
+            &mixer->auxilliary_out) != GST_FLOW_OK)
+      return FALSE;
+  }
+
+  if (mixer->primary_out == NULL)
+    return FALSE;
+
+  converted_buffer = mixer->primary_out;
+  v = 0;
+  n = gst_buffer_n_memory (converted_buffer);
+  g_assert (n == GST_VIDEO_INFO_N_PLANES (out_info) * views);
+  for (v = 0; v < views; v++) {
+    gst_buffer_add_video_meta_full (converted_buffer, v,
+        GST_VIDEO_INFO_FORMAT (out_info),
+        GST_VIDEO_INFO_WIDTH (out_info),
+        GST_VIDEO_INFO_HEIGHT (out_info),
+        GST_VIDEO_INFO_N_PLANES (out_info), out_info->offset, out_info->stride);
+    if (mixer->auxilliary_out) {
+      gst_buffer_add_video_meta_full (mixer->auxilliary_out, v,
+          GST_VIDEO_INFO_FORMAT (out_info),
+          GST_VIDEO_INFO_WIDTH (out_info),
+          GST_VIDEO_INFO_HEIGHT (out_info),
+          GST_VIDEO_INFO_N_PLANES (out_info), out_info->offset,
+          out_info->stride);
+    }
+  }
+
+  return TRUE;
+}
+
+/* Iterate the input sink pads, and choose the blend format
+ * we will generate before output conversion, which is RGBA
+ * at some suitable size */
+static void
+gst_gl_stereo_mix_find_best_format (GstVideoAggregator * vagg,
+    GstCaps * downstream_caps, GstVideoInfo * best_info,
+    gboolean * at_least_one_alpha)
+{
+  GstGLStereoMix *mix = GST_GL_STEREO_MIX (vagg);
+  GList *l;
+  gint best_width = -1, best_height = -1;
+  gdouble best_fps = -1, cur_fps;
+  gint best_fps_n = 0, best_fps_d = 1;
+  GstVideoInfo *mix_info;
+  GstCaps *blend_caps, *tmp_caps;
+
+  /* We'll deal with alpha internally, so just tell aggregator to
+   * be quiet */
+  *at_least_one_alpha = FALSE;
+
+  GST_OBJECT_LOCK (vagg);
+
+  for (l = GST_ELEMENT (vagg)->sinkpads; l; l = l->next) {
+    GstVideoAggregatorPad *pad = l->data;
+    GstVideoInfo tmp = pad->info;
+    gint this_width, this_height;
+    gint fps_n, fps_d;
+
+    if (!pad->info.finfo)
+      continue;
+
+    /* This can happen if we release a pad and another pad hasn't been negotiated_caps yet */
+    if (GST_VIDEO_INFO_FORMAT (&pad->info) == GST_VIDEO_FORMAT_UNKNOWN)
+      continue;
+
+    /* Convert to per-view width/height for unpacked forms */
+    gst_video_multiview_video_info_change_mode (&tmp,
+        GST_VIDEO_MULTIVIEW_MODE_SEPARATED, GST_VIDEO_MULTIVIEW_FLAGS_NONE);
+
+    this_width = GST_VIDEO_INFO_WIDTH (&tmp);
+    this_height = GST_VIDEO_INFO_HEIGHT (&tmp);
+    fps_n = GST_VIDEO_INFO_FPS_N (&tmp);
+    fps_d = GST_VIDEO_INFO_FPS_D (&tmp);
+
+    GST_INFO_OBJECT (vagg, "Input pad %" GST_PTR_FORMAT
+        " w %u h %u", pad, this_width, this_height);
+
+    if (this_width == 0 || this_height == 0)
+      continue;
+
+    if (best_width < this_width)
+      best_width = this_width;
+    if (best_height < this_height)
+      best_height = this_height;
+
+    if (fps_d == 0)
+      cur_fps = 0.0;
+    else
+      gst_util_fraction_to_double (fps_n, fps_d, &cur_fps);
+
+    if (best_fps < cur_fps) {
+      best_fps = cur_fps;
+      best_fps_n = fps_n;
+      best_fps_d = fps_d;
+    }
+
+    /* FIXME: Preserve PAR for at least one input when different sized inputs */
+  }
+  GST_OBJECT_UNLOCK (vagg);
+
+  mix_info = &mix->mix_info;
+  gst_video_info_set_format (mix_info, GST_VIDEO_FORMAT_RGBA, best_width,
+      best_height);
+
+  GST_VIDEO_INFO_FPS_N (mix_info) = best_fps_n;
+  GST_VIDEO_INFO_FPS_D (mix_info) = best_fps_d;
+
+  GST_VIDEO_INFO_MULTIVIEW_MODE (mix_info) = GST_VIDEO_MULTIVIEW_MODE_SEPARATED;
+  GST_VIDEO_INFO_VIEWS (mix_info) = 2;
+
+  /* FIXME: If input is marked as flipped or flopped, preserve those flags */
+  GST_VIDEO_INFO_MULTIVIEW_FLAGS (mix_info) = GST_VIDEO_MULTIVIEW_FLAGS_NONE;
+
+  /* Choose our output format based on downstream preferences */
+  blend_caps = gst_video_info_to_caps (mix_info);
+
+  gst_caps_set_features (blend_caps, 0,
+      gst_caps_features_from_string (GST_CAPS_FEATURE_MEMORY_GL_MEMORY));
+
+  tmp_caps = get_converted_caps (GST_GL_STEREO_MIX (vagg), blend_caps);
+  gst_caps_unref (blend_caps);
+
+  if (mix->out_caps)
+    gst_caps_unref (mix->out_caps);
+
+  mix->out_caps = gst_caps_intersect (downstream_caps, tmp_caps);
+  gst_caps_unref (tmp_caps);
+
+  GST_DEBUG_OBJECT (vagg, "Possible output caps %" GST_PTR_FORMAT,
+      mix->out_caps);
+  /* Tell videoaggregator our preferred size. Actual info gets
+   * overridden during caps nego */
+  *best_info = *mix_info;
+}