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pango: Add a property to compensate for display response time

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When measuring video latency, one mechanism involves taking a photo
with a camera of two screens showing the test video overlayed with
timeoverlay or clockoverlay. In these cases, if the display's pixel
response time is crappy, you will see ghosting due to which it can be
quite difficult to discern what the current timestamp being shown is.

This commit adds a property that *also* shows the timestamp in
a different (sequentially predictable) location every frame, which
makes it easy to tell what the latest rendered timestamp is.

For bonus points, you can also use the fade-time of the previous frame
to measure with sub-framerate accuracy when the photo was taken, not
just clamped to the framerate, giving you a higher precision latency
value.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6935>
This commit is contained in:
Nirbheek Chauhan 2024-05-28 13:37:39 +05:30 committed by GStreamer Marge Bot
parent afb62e98c7
commit a1463637e0
3 changed files with 82 additions and 4 deletions
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12
subprojects/gst-plugins-base/docs/plugins/gst_plugins_cache.json
View file

@ -9309,6 +9309,18 @@
"type": "guint",
"writable": true
},
"response-time-compensation": {
"blurb": "Render twice in a moving pattern to mitigate display response time causing ghosting",
"conditionally-available": false,
"construct": false,
"construct-only": false,
"controllable": false,
"default": "false",
"mutable": "null",
"readable": true,
"type": "gboolean",
"writable": true
},
"scale-mode": {
"blurb": "Scale text to compensate for and avoid distortion by subsequent video scaling.",
"conditionally-available": false,

73
subprojects/gst-plugins-base/ext/pango/gstbasetextoverlay.c
View file

@ -72,6 +72,7 @@
#define DEFAULT_PROP_TEXT_Y 0
#define DEFAULT_PROP_TEXT_WIDTH 1
#define DEFAULT_PROP_TEXT_HEIGHT 1
#define DEFAULT_PROP_ALT_RENDER FALSE
#define MINIMUM_OUTLINE_OFFSET 1.0
#define DEFAULT_SCALE_BASIS 640
@ -109,6 +110,7 @@ enum
PROP_TEXT_Y,
PROP_TEXT_WIDTH,
PROP_TEXT_HEIGHT,
PROP_ALT_RENDER,
PROP_LAST
};
@ -637,6 +639,34 @@ gst_base_text_overlay_class_init (GstBaseTextOverlayClass * klass)
1, 100, 100, 1, DEFAULT_PROP_SCALE_PAR_N, DEFAULT_PROP_SCALE_PAR_D,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
/**
* GstBaseTextOverlay:response-time-compensation:
*
* Compensate for display response time by doing a second text render in
* a slightly different (sequential and non-overlapping) place every frame.
*
* On all current displays, after a pixel is told to show a different color
* value, there is a "response time" after which the transition from the
* previous color to the new color is complete. On some displays this can
* take tens of milliseconds to complete, causing the previous frame's text
* render to overlap with the current frame's text render.
*
* This makes text renders that have the same position but change contents
* every frame impossible to use on displays with bad response times, such
* as when using clockoverlay and timeoverlay.
*
* Note that this is different from display lag/latency, which is an
* inherent property of the display and cannot be compensated for.
*
* Since: 1.26
*/
g_object_class_install_property (G_OBJECT_CLASS (klass), PROP_ALT_RENDER,
g_param_spec_boolean ("response-time-compensation",
"Display Response Time Compensation",
"Render twice in a moving pattern to mitigate display response time "
"causing ghosting", DEFAULT_PROP_ALT_RENDER, G_PARAM_READWRITE
| G_PARAM_STATIC_STRINGS));
gst_type_mark_as_plugin_api (GST_TYPE_BASE_TEXT_OVERLAY_HALIGN, 0);
gst_type_mark_as_plugin_api (GST_TYPE_BASE_TEXT_OVERLAY_VALIGN, 0);
gst_type_mark_as_plugin_api (GST_TYPE_BASE_TEXT_OVERLAY_LINE_ALIGN, 0);
@ -770,6 +800,7 @@ gst_base_text_overlay_init (GstBaseTextOverlay * overlay,
overlay->scale_mode = DEFAULT_PROP_SCALE_MODE;
overlay->scale_par_n = DEFAULT_PROP_SCALE_PAR_N;
overlay->scale_par_d = DEFAULT_PROP_SCALE_PAR_D;
overlay->alt_render = DEFAULT_PROP_ALT_RENDER;
overlay->line_align = DEFAULT_PROP_LINE_ALIGNMENT;
pango_layout_set_alignment (overlay->layout,
@ -1155,6 +1186,9 @@ gst_base_text_overlay_set_property (GObject * object, guint prop_id,
case PROP_SHADING_VALUE:
overlay->shading_value = g_value_get_uint (value);
break;
case PROP_ALT_RENDER:
overlay->alt_render = g_value_get_boolean (value);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
@ -1248,6 +1282,9 @@ gst_base_text_overlay_get_property (GObject * object, guint prop_id,
case PROP_SHADING_VALUE:
g_value_set_uint (value, overlay->shading_value);
break;
case PROP_ALT_RENDER:
g_value_set_boolean (value, overlay->alt_render);
break;
case PROP_FONT_DESC:
{
const PangoFontDescription *desc;
@ -1654,8 +1691,9 @@ gst_base_text_overlay_get_pos (GstBaseTextOverlay * overlay,
static inline void
gst_base_text_overlay_set_composition (GstBaseTextOverlay * overlay)
{
gint xpos, ypos;
GstVideoOverlayRectangle *rectangle;
static gint alt_idx;
gint xpos, ypos, alt_xpos, alt_ypos;
GstVideoOverlayRectangle *rectangle, *alt_rect = NULL;
if (overlay->text_image) {
gint render_width, render_height;
@ -1669,8 +1707,8 @@ gst_base_text_overlay_set_composition (GstBaseTextOverlay * overlay)
"updating composition for '%s' with window size %dx%d, "
"buffer size %dx%d, render size %dx%d and position (%d, %d)",
overlay->default_text, overlay->window_width, overlay->window_height,
overlay->text_width, overlay->text_height, render_width,
render_height, xpos, ypos);
overlay->text_width, overlay->text_height, render_width, render_height,
xpos, ypos);
gst_buffer_add_video_meta (overlay->text_image, GST_VIDEO_FRAME_FLAG_NONE,
GST_VIDEO_OVERLAY_COMPOSITION_FORMAT_RGB,
@ -1680,6 +1718,27 @@ gst_base_text_overlay_set_composition (GstBaseTextOverlay * overlay)
xpos, ypos, render_width, render_height,
GST_VIDEO_OVERLAY_FORMAT_FLAG_PREMULTIPLIED_ALPHA);
if (overlay->alt_render) {
gint num_x = (overlay->window_width - xpos) / render_width;
gint num_y = (overlay->window_height - ypos) / render_height;
if (num_x < 2 && num_y < 2) {
GST_ERROR ("Not enough space on the frame for an alternate position");
} else {
/* Find the next available slot in sequence for the secondary/alt
* display of the text overlay rectangle. We want to go up to down,
* left to right, all wrapping. */
alt_xpos = xpos + (alt_idx / num_y) * render_width;
alt_ypos = ypos + (alt_idx % num_y) * render_height;
alt_rect = gst_video_overlay_rectangle_new_raw (overlay->text_image,
alt_xpos, alt_ypos, render_width, render_height,
GST_VIDEO_OVERLAY_FORMAT_FLAG_PREMULTIPLIED_ALPHA);
/* Increment with wrapping */
alt_idx++;
alt_idx %= (num_x * num_y);
}
}
if (overlay->composition)
gst_video_overlay_composition_unref (overlay->composition);
@ -1692,6 +1751,12 @@ gst_base_text_overlay_set_composition (GstBaseTextOverlay * overlay)
overlay->composition = gst_video_overlay_composition_new (rectangle);
}
if (alt_rect) {
gst_video_overlay_composition_add_rectangle (overlay->composition,
alt_rect);
gst_video_overlay_rectangle_unref (alt_rect);
}
gst_video_overlay_rectangle_unref (rectangle);
} else if (overlay->composition) {

1
subprojects/gst-plugins-base/ext/pango/gstbasetextoverlay.h
View file

@ -194,6 +194,7 @@ struct _GstBaseTextOverlay {
GstBaseTextOverlayScaleMode scale_mode;
gint scale_par_n;
gint scale_par_d;
gboolean alt_render;
/* text pad format */
gboolean have_pango_markup;