avdevice: deprecate opengl outdev

Signed-off-by: J. Dekker <jdek@itanimul.li>

doc/outdevs.texi

@@ -302,7 +302,7 @@ ffmpeg -re -i INPUT -c:v rawvideo -pix_fmt bgra -f fbdev /dev/fb0
 See also @url{http://linux-fbdev.sourceforge.net/}, and fbset(1).
 
 @section opengl
-OpenGL output device.
+OpenGL output device. Deprecated and will be removed.
 
 To enable this output device you need to configure FFmpeg with @code{--enable-opengl}.
 

libavdevice/opengl_enc.c

@@ -224,6 +224,8 @@ typedef struct OpenGLContext {
     int picture_height;                ///< Rendered height
     int window_width;
     int window_height;
+
+    int warned;
 } OpenGLContext;
 
 static const struct OpenGLFormatDesc {
@@ -1060,6 +1062,15 @@ static av_cold int opengl_write_header(AVFormatContext *h)
     AVStream *st;
     int ret;
 
+    if (!opengl->warned) {
+        av_log(opengl, AV_LOG_WARNING,
+            "The opengl output device is deprecated due to being fundamentally incompatible with libavformat API. "
+            "For monitoring purposes in ffmpeg you can output to a file or use pipes and a video player.\n"
+            "Example: ffmpeg -i INPUT -f nut -c:v rawvideo - | ffplay -\n"
+        );
+        opengl->warned = 1;
+    }
+
     if (h->nb_streams != 1 ||
         par->codec_type != AVMEDIA_TYPE_VIDEO ||
         (par->codec_id != AV_CODEC_ID_WRAPPED_AVFRAME && par->codec_id != AV_CODEC_ID_RAWVIDEO)) {

libavdevice/version_major.h

@@ -35,5 +35,7 @@
 
 // reminder to remove the bktr device on next major bump
 #define FF_API_BKTR_DEVICE (LIBAVDEVICE_VERSION_MAJOR < 62)
+// reminder to remove the opengl device on next major bump
+#define FF_API_OPENGL_DEVICE (LIBAVDEVICE_VERSION_MAJOR < 62)
 
 #endif /* AVDEVICE_VERSION_MAJOR_H */