debug: add new element fakevideodec

The fake video decoder ignores input bitstream except
to enforce caps restrictions. It reads video width,
height and framerate from caps. Then it just pushes
video frames without doing any decoding.

The fake video decoder just draws a snake moving from
left to right in the middle of the frame. This is a
light weight drawing while it still provides an idea
about how smooth is the rendering.

The fake video decoder inherits from GstVideoDecoder.
It is useful to measure how smooth will be the whole
rendering pipeline if you had the most efficient video
decoder. Also useful to bisect issues for example when
suspecting issues in a specific video decoder.

Handles mpeg2, mpeg4, h263, h264, theora, vp8, wmv3, msmpeg,
flash-video, vp6, vp9, wmv1, wmv2, divx but more can be
added if needed.

For now it can only output RGBA, RGBx, BGRA, BGRx.

Its rank is 0 (none) but I added a property to change it so
that it can be selected by decodebin.

gst-launch-1.0 fakevideodec rank=512 \
  playbin uri=http://clips.vorwaerts-gmbh.de/big_buck_bunny.mp4

http://bugzilla.gnome.org/show_bug.cgi?id=723778

Closes #679

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5636>

subprojects/gst-plugins-base/docs/plugins/gst_plugins_cache.json

@@ -1715,6 +1715,44 @@
         "tracers": {},
         "url": "Unknown package origin"
     },
+    "basedebug": {
+        "description": "elements for testing and debugging",
+        "elements": {
+            "fakevideodec": {
+                "author": "Julien Isorce <julien.isorce@gmail.com>",
+                "description": "Fake video decoder",
+                "hierarchy": [
+                    "GstFakeVideoDec",
+                    "GstVideoDecoder",
+                    "GstElement",
+                    "GstObject",
+                    "GInitiallyUnowned",
+                    "GObject"
+                ],
+                "klass": "Codec/Decoder/Video",
+                "pad-templates": {
+                    "sink": {
+                        "caps": "video/x-h264:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\n         parsed: true\nvideo/x-h263:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\n         parsed: true\nvideo/x-theora:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-vp6:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-vp6-flash:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-vp8:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-vp9:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-divx:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-msmpeg:\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/mpeg:\n    mpegversion: { (int)1, (int)2, (int)4 }\n   systemstream: false\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-flash-video:\n     flvversion: 1\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-raw:\n         format: { RGBA, RGBx, BGRA, BGRx, RGB16 }\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\nvideo/x-wmv:\n     wmvversion: { (int)1, (int)2, (int)3 }\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 1/1, 2147483647/1 ]\n",
+                        "direction": "sink",
+                        "presence": "always"
+                    },
+                    "src": {
+                        "caps": "video/x-raw:\n         format: { RGBA, RGBx, BGRA, BGRx, RGB16 }\n          width: [ 1, 2147483647 ]\n         height: [ 1, 2147483647 ]\n      framerate: [ 0/1, 2147483647/1 ]\n",
+                        "direction": "src",
+                        "presence": "always"
+                    }
+                },
+                "rank": "none"
+            }
+        },
+        "filename": "gstbasedebug",
+        "license": "LGPL",
+        "other-types": {},
+        "package": "GStreamer Base Plug-ins",
+        "source": "gst-plugins-base",
+        "tracers": {},
+        "url": "Unknown package origin"
+    },
     "cdparanoia": {
         "description": "Read audio from CD in paranoid mode",
         "elements": {

subprojects/gst-plugins-base/gst/debugutils/gstdebug.c

@@ -0,0 +1,53 @@
+/* GStreamer
+ * Copyright (C) 2004 Benjamin Otte <otte@gnome.org>
+ * Copyright (C) 2020 Huawei Technologies Co., Ltd.
+ *   @Author: Stéphane Cerveau <stephane.cerveau@collabora.com>
+ *
+ * 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.
+ */
+/**
+ * plugin-basedebug:
+ * @short_description: elements for testing and debugging
+ *
+ * This plugin contains elements that are useful for debugging and testing
+ * purposes.
+ *
+ * Since: 1.24
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include <gst/gst.h>
+
+#include "gstdebugutilselements.h"
+
+static gboolean
+plugin_init (GstPlugin * plugin)
+{
+  gboolean ret = FALSE;
+
+  ret |= GST_ELEMENT_REGISTER (fakevideodec, plugin);
+
+  return ret;
+}
+
+GST_PLUGIN_DEFINE (GST_VERSION_MAJOR,
+    GST_VERSION_MINOR,
+    basedebug,
+    "elements for testing and debugging",
+    plugin_init, VERSION, "LGPL", GST_PACKAGE_NAME, GST_PACKAGE_ORIGIN)

subprojects/gst-plugins-base/gst/debugutils/gstdebugutilselements.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2004 Benjamin Otte <otte@gnome.org>
+ * Copyright (C) 2020 Huawei Technologies Co., Ltd.
+ *   @Author: Stéphane Cerveau <stephane.cerveau@collabora.com>
+ *
+ * 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.
+ */
+
+#ifndef __GST_DEBUGUTILS_ELEMENTS_H__
+#define __GST_DEBUGUTILS_ELEMENTS_H__
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/gst.h>
+
+G_BEGIN_DECLS
+
+GST_ELEMENT_REGISTER_DECLARE (fakevideodec);
+
+G_END_DECLS
+
+#endif /* __GST_DEBUGUTILS_ELEMENTS_H__ */

subprojects/gst-plugins-base/gst/debugutils/gstfakevideodec.c

@@ -0,0 +1,474 @@
+/* GStreamer
+ * Copyright (C) 2019 Julien Isorce <julien.isorce@gmail.com>
+ * Copyright (C) 2023 Thibault Saunier <tsaunier@igalia.com>
+ *
+ * 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.
+ *
+ */
+/**
+ * element-fakevideodec:
+ *
+ * The fake video decoder ignores input bitstream except
+ * to enforce caps restrictions. It reads video `width`,
+ * `height` and `framerate` from caps. Then it just pushes
+ * video frames without doing any decoding. It can Also
+ * handle raw frames decoding them as they come, faking
+ * that it is decoding them.
+ *
+ * When faking decoding encoded data, it draws a snake moving from
+ * left to right in the middle of the frame. This is a
+ * light weight drawing while it still provides an idea
+ * about how smooth is the rendering.
+ *
+ * The fake video decoder inherits from GstVideoDecoder.
+ * It is useful to measure how smooth will be the whole
+ * rendering pipeline if you had the most efficient video
+ * decoder. Also useful to bisect issues for example when
+ * suspecting issues in a specific video decoder.
+ *
+ * It is also useful to to use it to test the #GstVideoDecoder base
+ * class.
+ *
+ * ## Examples:
+ *
+ * ### Fake decoding raw frames
+ *
+ * ```
+ * $ gst-launch-1.0 videotestsrc !  fakevideodec ! videoconvert ! autovideosink
+ * ```
+ *
+ * ### False decoding encoded framers
+ *
+ * ```
+ * $ GST_PLUGIN_FEATURE_RANK=fakevideodec:1000 gstdump gst-launch-1.0 playbin3 uri=file:///path/to/video
+ *
+ * ```
+ * Since: 1.24
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "gstfakevideodec.h"
+
+#include <gst/video/gstvideometa.h>
+#include <gst/video/gstvideopool.h>
+
+#include <stdio.h>
+#include <string.h>
+
+
+GST_DEBUG_CATEGORY_STATIC (gst_fake_videodec_debug);
+#define GST_CAT_DEFAULT gst_fake_videodec_debug
+
+static gboolean gst_fake_video_dec_start (GstVideoDecoder * decoder);
+static gboolean gst_fake_video_dec_stop (GstVideoDecoder * decoder);
+static gboolean gst_fake_video_dec_set_format (GstVideoDecoder * decoder,
+    GstVideoCodecState * state);
+static gboolean gst_fake_video_dec_negotiate (GstVideoDecoder * decoder);
+static gboolean gst_fake_video_dec_flush (GstVideoDecoder * decoder);
+static GstFlowReturn gst_fake_video_dec_handle_frame (GstVideoDecoder * decoder,
+    GstVideoCodecFrame * frame);
+static gboolean gst_fake_video_dec_decide_allocation (GstVideoDecoder * decoder,
+    GstQuery * query);
+
+#define FAKE_VIDEO_DEC_CAPS_COMMON ", width=(int) [1, MAX], height=(int) [1, MAX], framerate=(fraction) [1, MAX]"
+#define FAKE_VIDEO_DEC_CAPS_COMMON_PARSED FAKE_VIDEO_DEC_CAPS_COMMON ", parsed = (boolean) true"
+#define FAKE_VIDEO_DEC_CAPS "video/x-h264" FAKE_VIDEO_DEC_CAPS_COMMON_PARSED ";" \
+    "video/x-h263" FAKE_VIDEO_DEC_CAPS_COMMON_PARSED ";" \
+    "video/x-theora" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-vp6" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-vp6-flash" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-vp8" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-vp9" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-divx" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-msmpeg" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/mpeg, mpegversion=(int) {1, 2, 4}, systemstream=(boolean) false" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-flash-video, flvversion=(int) 1" FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-raw,format={ RGBA, RGBx, BGRA, BGRx, RGB16} " FAKE_VIDEO_DEC_CAPS_COMMON ";" \
+    "video/x-wmv, wmvversion=(int) {1, 2, 3}" FAKE_VIDEO_DEC_CAPS_COMMON
+
+static GstStaticPadTemplate gst_fake_video_dec_sink_template =
+GST_STATIC_PAD_TEMPLATE ("sink",
+    GST_PAD_SINK,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS (FAKE_VIDEO_DEC_CAPS)
+    );
+
+static GstStaticPadTemplate gst_fake_video_dec_src_template =
+GST_STATIC_PAD_TEMPLATE ("src",
+    GST_PAD_SRC,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS (GST_VIDEO_CAPS_MAKE ("{ RGBA, RGBx, BGRA, BGRx, RGB16}"))
+    );
+
+#define parent_class gst_fake_video_dec_parent_class
+G_DEFINE_TYPE (GstFakeVideoDec, gst_fake_video_dec, GST_TYPE_VIDEO_DECODER);
+GST_ELEMENT_REGISTER_DEFINE (fakevideodec, "fakevideodec",
+    GST_RANK_NONE, gst_fake_video_dec_get_type ());
+
+static void
+gst_fake_video_dec_class_init (GstFakeVideoDecClass * klass)
+{
+  GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
+  GstVideoDecoderClass *base_video_decoder_class =
+      GST_VIDEO_DECODER_CLASS (klass);
+
+  gst_element_class_add_pad_template (element_class,
+      gst_static_pad_template_get (&gst_fake_video_dec_src_template));
+  gst_element_class_add_pad_template (element_class,
+      gst_static_pad_template_get (&gst_fake_video_dec_sink_template));
+
+  gst_element_class_set_static_metadata (element_class,
+      "Fake Video Decoder",
+      "Codec/Decoder/Video",
+      "Fake video decoder", "Julien Isorce <julien.isorce@gmail.com>");
+
+  base_video_decoder_class->start =
+      GST_DEBUG_FUNCPTR (gst_fake_video_dec_start);
+  base_video_decoder_class->stop = GST_DEBUG_FUNCPTR (gst_fake_video_dec_stop);
+  base_video_decoder_class->flush =
+      GST_DEBUG_FUNCPTR (gst_fake_video_dec_flush);
+  base_video_decoder_class->set_format =
+      GST_DEBUG_FUNCPTR (gst_fake_video_dec_set_format);
+  base_video_decoder_class->negotiate =
+      GST_DEBUG_FUNCPTR (gst_fake_video_dec_negotiate);
+  base_video_decoder_class->handle_frame =
+      GST_DEBUG_FUNCPTR (gst_fake_video_dec_handle_frame);
+  base_video_decoder_class->decide_allocation =
+      gst_fake_video_dec_decide_allocation;
+
+  GST_DEBUG_CATEGORY_INIT (gst_fake_videodec_debug, "fakevideodec", 0,
+      "Fake Video Decoder");
+}
+
+static void
+gst_fake_video_dec_init (GstFakeVideoDec * dec)
+{
+  GstVideoDecoder *bdec = GST_VIDEO_DECODER (dec);
+
+  GST_DEBUG_OBJECT (dec, "Initialize fake video decoder");
+
+  gst_video_decoder_set_packetized (bdec, TRUE);
+  dec->min_buffers = 0;
+  dec->snake_current_step = 0;
+  dec->snake_max_steps = 0;
+  dec->snake_length = 0;
+}
+
+static gboolean
+gst_fake_video_dec_start (GstVideoDecoder * decoder)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (decoder);
+
+  GST_DEBUG_OBJECT (dec, "start");
+
+  dec->min_buffers = 0;
+  dec->snake_current_step = 0;
+
+  return TRUE;
+}
+
+static gboolean
+gst_fake_video_dec_stop (GstVideoDecoder * base_video_decoder)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (base_video_decoder);
+
+  GST_DEBUG_OBJECT (dec, "stop");
+
+  if (dec->output_state) {
+    gst_video_codec_state_unref (dec->output_state);
+    dec->output_state = NULL;
+  }
+
+  if (dec->input_state) {
+    gst_video_codec_state_unref (dec->input_state);
+    dec->input_state = NULL;
+  }
+
+  return TRUE;
+}
+
+static gboolean
+gst_fake_video_dec_set_format (GstVideoDecoder * decoder,
+    GstVideoCodecState * state)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (decoder);
+  GstCaps *templ_caps = NULL;
+  GstCaps *intersection = NULL;
+  GstVideoInfo info;
+  gdouble fps = 0;
+
+  GST_DEBUG_OBJECT (dec, "set format");
+
+  /* select what downstream want of support the best */
+
+  templ_caps = gst_pad_get_pad_template_caps (GST_VIDEO_DECODER_SRC_PAD (dec));
+  intersection =
+      gst_pad_peer_query_caps (GST_VIDEO_DECODER_SRC_PAD (dec), templ_caps);
+  gst_caps_unref (templ_caps);
+
+  GST_DEBUG_OBJECT (dec, "Allowed downstream caps: %" GST_PTR_FORMAT,
+      intersection);
+
+  intersection = gst_caps_truncate (intersection);
+  intersection = gst_caps_fixate (intersection);
+
+  gst_video_info_init (&info);
+  if (!gst_video_info_from_caps (&info, intersection)) {
+    GST_WARNING_OBJECT (dec,
+        "failed to parse intersection with downstream caps %" GST_PTR_FORMAT,
+        intersection);
+    gst_caps_unref (intersection);
+    return FALSE;
+  }
+  gst_caps_unref (intersection);
+  intersection = NULL;
+
+  if (dec->input_state)
+    gst_video_codec_state_unref (dec->input_state);
+  dec->input_state = gst_video_codec_state_ref (state);
+
+  dec->output_state =
+      gst_video_decoder_set_output_state (GST_VIDEO_DECODER (dec),
+      GST_VIDEO_INFO_FORMAT (&info), dec->input_state->info.width,
+      dec->input_state->info.height, dec->input_state);
+  gst_video_decoder_negotiate (GST_VIDEO_DECODER (dec));
+
+  gst_util_fraction_to_double (dec->output_state->info.fps_n,
+      dec->output_state->info.fps_d, &fps);
+
+  if (fps < 1 || fps > 60) {
+    GST_ERROR_OBJECT (dec, "unsupported framerate %d / %d",
+        dec->output_state->info.fps_n, dec->output_state->info.fps_d);
+    return FALSE;
+  }
+
+  dec->snake_max_steps = (guint) fps;
+  dec->snake_length = dec->output_state->info.width / fps;
+
+  if (dec->snake_length == 0) {
+    GST_ERROR_OBJECT (dec,
+        "unsupported framerate %d / %d or frame width too small %d",
+        dec->output_state->info.fps_n, dec->output_state->info.fps_d,
+        dec->output_state->info.width);
+    return FALSE;
+  }
+
+  GST_DEBUG_OBJECT (dec,
+      "width: %d, height: %d, fps_n: %d, fps_d: %d, snake length %d",
+      dec->output_state->info.width, dec->output_state->info.height,
+      dec->output_state->info.fps_n, dec->output_state->info.fps_d,
+      dec->snake_length);
+
+  return TRUE;
+}
+
+static GstFlowReturn
+gst_fake_video_dec_init_buffer (GstFakeVideoDec * dec, GstBuffer * buffer)
+{
+  GstMapInfo minfo;
+
+  if (!gst_buffer_map (buffer, &minfo, GST_MAP_READ)) {
+    GST_ERROR_OBJECT (dec, "Failed to map input buffer");
+    return GST_FLOW_ERROR;
+  }
+
+  /* Make the frames entirely black just once. */
+  memset (minfo.data, 0, minfo.maxsize);
+
+  gst_buffer_unmap (buffer, &minfo);
+
+  return GST_FLOW_OK;
+}
+
+static gboolean
+gst_fake_video_dec_negotiate (GstVideoDecoder * decoder)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (decoder);
+  GstVideoCodecFrame *frame = NULL;
+  gboolean ret = TRUE;
+  guint i = 0;
+
+  if (!GST_VIDEO_DECODER_CLASS (parent_class)->negotiate (decoder))
+    return FALSE;
+
+  GST_DEBUG_OBJECT (dec, "negotiate");
+
+  frame = g_slice_new0 (GstVideoCodecFrame);
+
+  for (i = 0; i < dec->min_buffers; ++i) {
+    ret =
+        gst_video_decoder_allocate_output_frame (decoder, frame) == GST_FLOW_OK;
+    if (!ret)
+      break;
+    gst_fake_video_dec_init_buffer (dec, frame->output_buffer);
+    gst_buffer_replace (&frame->output_buffer, NULL);
+  }
+
+  g_slice_free (GstVideoCodecFrame, frame);
+
+  return ret;
+}
+
+static gboolean
+gst_fake_video_dec_flush (GstVideoDecoder * decoder)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (decoder);
+
+  GST_DEBUG_OBJECT (dec, "flush");
+
+  return TRUE;
+}
+
+static void
+gst_fake_video_dec_snake_next_step (GstFakeVideoDec * dec)
+{
+  if (dec->snake_current_step < dec->snake_max_steps) {
+    ++dec->snake_current_step;
+    return;
+  }
+
+  dec->snake_current_step = 0;
+}
+
+static GstFlowReturn
+gst_fake_video_dec_fill_buffer (GstFakeVideoDec * dec, GstBuffer * buffer)
+{
+  gint height = 0;
+  guint offset = 0;
+  gint stride = 0;
+  guint depth = 0;
+  guint8 *data = NULL;
+  GstVideoFrame frame;
+  GstVideoInfo *info = &dec->output_state->info;
+
+  if (!gst_video_frame_map (&frame, info, buffer, GST_MAP_WRITE)) {
+    GST_ERROR_OBJECT (dec, "Could not map video buffer");
+    return GST_FLOW_ERROR;
+  }
+
+  if (GST_VIDEO_FRAME_N_PLANES (&frame) != 1) {
+    GST_ERROR_OBJECT (dec, "Currently only support one video frame plane");
+    gst_video_frame_unmap (&frame);
+    return GST_FLOW_ERROR;
+  }
+
+  height = GST_VIDEO_FRAME_HEIGHT (&frame);
+  data = GST_VIDEO_FRAME_PLANE_DATA (&frame, 0);
+  offset = GST_VIDEO_FRAME_PLANE_OFFSET (&frame, 0);
+  stride = GST_VIDEO_FRAME_PLANE_STRIDE (&frame, 0);
+  depth = GST_VIDEO_FRAME_COMP_DEPTH (&frame, 0);
+
+  switch (GST_VIDEO_FRAME_FORMAT (&frame)) {
+    case GST_VIDEO_FORMAT_BGRA:
+    case GST_VIDEO_FORMAT_BGRx:
+    case GST_VIDEO_FORMAT_RGBA:
+    case GST_VIDEO_FORMAT_RGBx:
+    case GST_VIDEO_FORMAT_RGB16:
+    {
+      /* Erase the entire line where the snake is drawn. */
+      memset (data + offset + (height / 2) * stride, 0, stride * depth);
+      /* Draw a snake moving from left to right. */
+      memset (data + offset + (height / 2) * stride +
+          dec->snake_current_step * dec->snake_length * depth, 0xff,
+          dec->snake_length * depth);
+      break;
+    }
+    default:
+      GST_WARNING_OBJECT (dec, "Not supported video format %s",
+          gst_video_format_to_string (GST_VIDEO_FRAME_FORMAT (&frame)));
+      break;
+  }
+
+  gst_video_frame_unmap (&frame);
+
+  return GST_FLOW_OK;
+}
+
+static GstFlowReturn
+gst_fake_video_dec_handle_frame (GstVideoDecoder * decoder,
+    GstVideoCodecFrame * frame)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (decoder);
+  GstFlowReturn ret = GST_FLOW_OK;
+  GstMapInfo minfo;
+
+  GST_DEBUG_OBJECT (dec, "handle frame");
+
+  if (dec->input_state->info.finfo->format == GST_VIDEO_FORMAT_ENCODED) {
+    if (!gst_buffer_map (frame->input_buffer, &minfo, GST_MAP_READ)) {
+      GST_ERROR_OBJECT (dec, "Failed to map input buffer");
+      return GST_FLOW_ERROR;
+    }
+
+    GST_DEBUG_OBJECT (dec,
+        "input data size %" G_GSIZE_FORMAT ", PTS: %" GST_TIME_FORMAT,
+        minfo.size, GST_TIME_ARGS (frame->pts));
+
+    gst_buffer_unmap (frame->input_buffer, &minfo);
+
+    gst_fake_video_dec_snake_next_step (dec);
+    ret = gst_video_decoder_allocate_output_frame (decoder, frame);
+    if (ret != GST_FLOW_OK)
+      goto drop;
+    ret = gst_fake_video_dec_fill_buffer (dec, frame->output_buffer);
+    if (ret != GST_FLOW_OK)
+      goto drop;
+  } else {
+    frame->output_buffer = gst_buffer_ref (frame->input_buffer);
+  }
+
+  ret = gst_video_decoder_finish_frame (decoder, frame);
+  return ret;
+
+drop:
+  gst_video_decoder_drop_frame (decoder, frame);
+  return ret;
+}
+
+static gboolean
+gst_fake_video_dec_decide_allocation (GstVideoDecoder * bdec, GstQuery * query)
+{
+  GstFakeVideoDec *dec = GST_FAKE_VIDEO_DEC (bdec);
+  GstBufferPool *pool = NULL;
+  GstStructure *config = NULL;
+  guint min_buffers = 0;
+
+  if (!GST_VIDEO_DECODER_CLASS (parent_class)->decide_allocation (bdec, query))
+    return FALSE;
+
+  GST_DEBUG_OBJECT (dec, "decide allocation");
+
+  g_assert (gst_query_get_n_allocation_pools (query) > 0);
+  gst_query_parse_nth_allocation_pool (query, 0, &pool, NULL, &min_buffers,
+      NULL);
+  g_assert (pool != NULL);
+
+  /* Initialize at least 2 buffers. */
+  dec->min_buffers = MIN (min_buffers, 2);
+
+  config = gst_buffer_pool_get_config (pool);
+  if (gst_query_find_allocation_meta (query, GST_VIDEO_META_API_TYPE, NULL)) {
+    gst_buffer_pool_config_add_option (config,
+        GST_BUFFER_POOL_OPTION_VIDEO_META);
+  }
+  gst_buffer_pool_set_config (pool, config);
+  gst_object_unref (pool);
+
+  return TRUE;
+}

subprojects/gst-plugins-base/gst/debugutils/gstfakevideodec.h

@@ -0,0 +1,68 @@
+/* GStreamer
+ * Copyright (C) 2019 Julien Isorce <julien.isorce@gmail.com>
+ *
+ * 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.
+ *
+ */
+
+
+#ifndef __GST_FAKE_VIDEO_DEC_H__
+#define __GST_FAKE_VIDEO_DEC_H__
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/gst.h>
+#include <gst/video/gstvideodecoder.h>
+#include "gstdebugutilselements.h"
+
+G_BEGIN_DECLS
+#define GST_TYPE_FAKE_VIDEO_DEC \
+  (gst_fake_video_dec_get_type())
+#define GST_FAKE_VIDEO_DEC(obj) \
+  (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_FAKE_VIDEO_DEC,GstFakeVideoDec))
+#define GST_FAKE_VIDEO_DEC_CLASS(klass) \
+  (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_FAKE_VIDEO_DEC,GstFakeVideoDecClass))
+#define GST_IS_FAKE_VIDEO_DEC(obj) \
+  (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_FAKE_VIDEO_DEC))
+#define GST_IS_FAKE_VIDEO_DEC_CLASS(obj) \
+  (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_FAKE_VIDEO_DEC))
+typedef struct _GstFakeVideoDec GstFakeVideoDec;
+typedef struct _GstFakeVideoDecClass GstFakeVideoDecClass;
+
+struct _GstFakeVideoDec
+{
+  GstVideoDecoder base_video_decoder;
+
+  GstVideoCodecState *input_state;
+  GstVideoCodecState *output_state;
+
+  guint min_buffers;
+  guint snake_current_step;
+  guint snake_max_steps;
+  guint snake_length;
+};
+
+struct _GstFakeVideoDecClass
+{
+  GstVideoDecoderClass base_video_decoder_class;
+};
+
+GType gst_fake_video_dec_get_type (void);
+
+G_END_DECLS
+#endif /* __GST_FAKE_VIDEO_DEC_H__ */

subprojects/gst-plugins-base/gst/debugutils/meson.build

@@ -0,0 +1,11 @@
+gstdebug = library('gstbasedebug',
+  'gstdebug.c',
+  'gstfakevideodec.c',
+  c_args: gst_plugins_base_args,
+  include_directories : [configinc],
+  dependencies : [gst_dep, gst_base_dep, video_dep],
+  install : true,
+  install_dir : plugins_install_dir,
+)
+plugins += [gstdebug]
+

subprojects/gst-plugins-base/gst/meson.build

@@ -1,5 +1,5 @@
 foreach plugin : ['adder', 'app', 'audioconvert', 'audiomixer', 'audiorate', 'audioresample',
-                  'audiotestsrc', 'compositor', 'dsd', 'encoding', 'gio', 'overlaycomposition',
+                  'audiotestsrc', 'compositor', 'dsd', 'debugutils', 'encoding', 'gio', 'overlaycomposition',
                   'pbtypes', 'playback', 'rawparse', 'subparse', 'tcp', 'typefind',
                   'videoconvertscale', 'videorate', 'videotestsrc', 'volume']
   if not get_option(plugin).disabled()

subprojects/gst-plugins-base/meson_options.txt

@@ -36,6 +36,7 @@ option('audiorate', type : 'feature', value : 'auto')
 option('audioresample', type : 'feature', value : 'auto')
 option('audiotestsrc', type : 'feature', value : 'auto')
 option('compositor', type : 'feature', value : 'auto')
+option('debugutils', type : 'feature', value : 'auto')
 option('drm', type : 'feature', value : 'auto')
 option('dsd', type : 'feature', value : 'auto')
 option('encoding', type : 'feature', value : 'auto')