fix Full vs Restricted color issue by conversion to sRGB

thanks to @PancakeTAS for this discovery

CMakeLists.txt

@@ -32,7 +32,9 @@ if ( ( UNIX AND NOT APPLE ) OR USE_X11 )
 endif()
 
 if( UNIX AND NOT APPLE )
- add_definitions( -DSUPPRESS_AVAHI_COMPAT_WARNING )
+  add_definitions( -DSUPPRESS_AVAHI_COMPAT_WARNING )
+  # convert AirPlay colormap 1:3:7:1 to sRGB (1:1:7:1), needed on Linux and BSD
+  add_definitions( -DFULL_RANGE_RGB_FIX )
 else()
   set( CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE )
 endif()

README.html

@@ -1107,8 +1107,18 @@ <h1 id="usage">Usage</h1>
 <p><strong>-bt709</strong> A workaround for the failure of the older
 Video4Linux2 plugin to recognize Apple’s use of an uncommon (but
 permitted) “full-range color” variant of the bt709 color standard for
-digital TV. This is no longer needed by GStreamer-1.20.4 and backports
-from it.</p>
+digital TV. This was no longer needed by GStreamer-1.20.4 and backports
+from it, but appears to again be required in GStreamer-1.22 and
+later.</p>
+<p><strong>-srgb</strong> A workaround for a failure to display
+full-range 8-bit color [0-255], and instead restrict to limited range
+[16-235] “legal BT709” HDTV format. The workaround works on x86_64
+desktop systems, but does not yet work on Raspberry Pi. The issue may be
+fixed in a future GStreamer release: it only occurs in Linux and
+*BSD.</p>
+<p><strong>-srbg no</strong>. Disables the -srgb option, which is
+enabled by default in Linux and *BSD, but may be useless on Raspberry
+Pi, and may be unwanted, as it adds extra processing load.</p>
 <p><strong>-rpi</strong> Equivalent to “-v4l2” (Not valid for Raspberry
 Pi model 5, and removed in UxPlay 1.67)</p>
 <p><strong>-rpigl</strong> Equivalent to “-rpi -vs glimagesink”.

README.md

@@ -1121,8 +1121,19 @@ Video4Linux2. Equivalent to `-vd v4l2h264dec -vc v4l2convert`.
 
 **-bt709** A workaround for the failure of the older Video4Linux2 plugin
 to recognize Apple's use of an uncommon (but permitted) "full-range
-color" variant of the bt709 color standard for digital TV. This is no
-longer needed by GStreamer-1.20.4 and backports from it.
+color" variant of the bt709 color standard for digital TV. This was no
+longer needed by GStreamer-1.20.4 and backports from it, but appears to 
+again be required in GStreamer-1.22 and later.
+
+**-srgb** A workaround for a failure to display full-range 8-bit color
+[0-255], and instead restrict to limited range [16-235] "legal BT709"
+HDTV format.    The workaround works on x86_64 desktop systems, but
+does not yet work on Raspberry Pi.  The issue may be fixed in a future GStreamer
+release: it only occurs in Linux and \*BSD.
+
+**-srbg no**. Disables the -srgb option, which is enabled by default in
+Linux and *BSD, but may be useless on Raspberry Pi, and may be unwanted,
+as it adds extra processing load.
 
 **-rpi** Equivalent to "-v4l2" (Not valid for Raspberry Pi model 5, and
 removed in UxPlay 1.67)

README.txt

@@ -1122,8 +1122,19 @@ Video4Linux2. Equivalent to `-vd v4l2h264dec -vc v4l2convert`.
 
 **-bt709** A workaround for the failure of the older Video4Linux2 plugin
 to recognize Apple's use of an uncommon (but permitted) "full-range
-color" variant of the bt709 color standard for digital TV. This is no
-longer needed by GStreamer-1.20.4 and backports from it.
+color" variant of the bt709 color standard for digital TV. This was no
+longer needed by GStreamer-1.20.4 and backports from it, but appears to
+again be required in GStreamer-1.22 and later.
+
+**-srgb** A workaround for a failure to display full-range 8-bit color
+\[0-255\], and instead restrict to limited range \[16-235\] "legal
+BT709" HDTV format. The workaround works on x86_64 desktop systems, but
+does not yet work on Raspberry Pi. The issue may be fixed in a future
+GStreamer release: it only occurs in Linux and \*BSD.
+
+**-srbg no**. Disables the -srgb option, which is enabled by default in
+Linux and \*BSD, but may be useless on Raspberry Pi, and may be
+unwanted, as it adds extra processing load.
 
 **-rpi** Equivalent to "-v4l2" (Not valid for Raspberry Pi model 5, and
 removed in UxPlay 1.67)

renderers/video_renderer.c

@@ -128,14 +128,14 @@ static void append_videoflip (GString *launch, const videoflip_t *flip, const vi
     }
 }
 
-/* apple uses colorimetry=1:3:5:1                                *
+/* apple uses colorimetry that is detected as  1:3:7:1           * //previously 1:3:5:1 was seen
  * (not recognized by v4l2 plugin in Gstreamer  < 1.20.4)        *
  * See .../gst-libs/gst/video/video-color.h in gst-plugins-base  *
  * range = 1   -> GST_VIDEO_COLOR_RANGE_0_255      ("full RGB")  * 
  * matrix = 3  -> GST_VIDEO_COLOR_MATRIX_BT709                   *
- * transfer = 5 -> GST_VIDEO_TRANSFER_BT709                      *
+ * transfer = 7 -> GST_VIDEO_TRANSFER_SRGB                       * // previously GST_VIDEO_TRANSFER_BT709
  * primaries = 1 -> GST_VIDEO_COLOR_PRIMARIES_BT709              *
- * closest used by  GStreamer < 1.20.4 is BT709, 2:3:5:1 with    *                            *
+ * closest used by  GStreamer < 1.20.4 is BT709, 2:3:5:1 with    * // now use sRGB = 1:1:7:1    
  * range = 2 -> GST_VIDEO_COLOR_RANGE_16_235 ("limited RGB")     */  
 
 static const char h264_caps[]="video/x-h264,stream-format=(string)byte-stream,alignment=(string)au";

uxplay.1

@@ -87,6 +87,12 @@ UxPlay 1.71: An open\-source AirPlay mirroring (+ audio streaming) server:
 .TP
 \fB\-bt709\fR    Sometimes needed for Raspberry Pi models using Video4Linux2.
 .TP
+\fB\-srgb\fR     Display "Full range" [0-255] color, not "Limited Range"[16-235]
+.IP
+   This is a workaround for a GStreamer problem, until it is fixed.
+.PP
+\fB\-srgb\fR no  Disable srgb option (use when enabled by default: Linux, *BSD)
+.TP
 \fB\-as\fI sink\fR  Choose the GStreamer audiosink; default "autoaudiosink"
 .IP
    choices:pulsesink,alsasink,pipewiresink,osssink,oss4sink,

uxplay.cpp

@@ -72,6 +72,12 @@
 #define HIGHEST_PORT 65535
 #define NTP_TIMEOUT_LIMIT 5
 #define BT709_FIX "capssetter caps=\"video/x-h264, colorimetry=bt709\""
+#define SRGB_FIX  " ! video/x-raw,colorimetry=sRGB,format=RGB  ! "
+#ifdef FULL_RANGE_RGB_FIX
+  #define DEFAULT_SRGB_FIX true
+#else
+  #define DEFAULT_SRGB_FIX false
+#endif
 
 static std::string server_name = DEFAULT_NAME;
 static dnssd_t *dnssd = NULL;
@@ -122,6 +128,7 @@ static unsigned short display[5] = {0}, tcp[3] = {0}, udp[3] = {0};
 static bool debug_log = DEFAULT_DEBUG_LOG;
 static int log_level = LOGGER_INFO;
 static bool bt709_fix = false;
+static bool srgb_fix = DEFAULT_SRGB_FIX;
 static int nohold = 0;
 static bool nofreeze = false;
 static unsigned short raop_port;
@@ -640,7 +647,10 @@ static void print_info (char *name) {
     printf("          gtksink,waylandsink,osxvideosink,kmssink,d3d11videosink etc.\n");
     printf("-vs 0     Streamed audio only, with no video display window\n");
     printf("-v4l2     Use Video4Linux2 for GPU hardware h264 decoding\n");
-    printf("-bt709    Sometimes needed for Raspberry Pi models using Video4Linux2 \n"); 
+    printf("-bt709    Sometimes needed for Raspberry Pi models using Video4Linux2 \n");
+    printf("-srgb     Display \"Full range\" [0-255] color, not \"Limited Range\"[16-235]\n");
+    printf("          This is a workaround for a GStreamer problem, until it is fixed\n");
+    printf("-srgb no  Disable srgb option (use when enabled by default: Linux, *BSD)\n");
     printf("-as ...   Choose the GStreamer audiosink; default \"autoaudiosink\"\n");
     printf("          some choices:pulsesink,alsasink,pipewiresink,jackaudiosink,\n");
     printf("          osssink,oss4sink,osxaudiosink,wasapisink,directsoundsink.\n");
@@ -1003,7 +1013,7 @@ static void parse_arguments (int argc, char *argv[]) {
             fprintf(stderr,"     -rpifb was equivalent to \"-v4l2 -vs kmssink\"\n");
             fprintf(stderr,"     -rpigl was equivalent to \"-v4l2 -vs glimagesink\"\n");
             fprintf(stderr,"     -rpiwl was equivalent to \"-v4l2 -vs waylandsink\"\n");
-            fprintf(stderr,"     for GStreamer < 1.22, \"-bt709\" may also be needed\n");
+            fprintf(stderr,"     Option \"-bt709\" may also be needed for R Pi model 4B and earlier\n");
             exit(1);
         } else if (arg == "-fs" ) {
             fullscreen = true;
@@ -1078,6 +1088,15 @@ static void parse_arguments (int argc, char *argv[]) {
             }
         } else if (arg == "-bt709") {
             bt709_fix = true;
+        } else if (arg == "-srgb") {
+            srgb_fix = true;
+	    if (i <  argc - 1) {
+                if (strlen(argv[i+1]) == 2 && strncmp(argv[i+1], "no", 2) == 0) {
+                    srgb_fix = false;
+                    i++;
+                    continue;
+                }
+            }
         } else if (arg == "-nohold") {
             nohold = 1;
         } else if (arg == "-al") {
@@ -2170,6 +2189,12 @@ int main (int argc, char *argv[]) {
         video_parser.append(BT709_FIX);
     }
 
+    if (srgb_fix && use_video) {
+        std::string option = video_converter;
+        video_converter.append(SRGB_FIX);
+        video_converter.append(option);
+    }
+
     if (require_password && registration_list) {
         if (pairing_register == "") {
             const char * homedir = get_homedir();