lavc cuda conv: disable by default + note

The actual implementation has not been merged as for now, so disable
the stub by default in configure.ac.

Also add a notice suggesting the removal.

Author: MartinPulec

configure.ac

@@ -1897,10 +1897,10 @@ AC_ARG_ENABLE(libavcodec,
 )
 
 AC_ARG_ENABLE(lavc-cuda-conv,
-      AS_HELP_STRING([--disable-lavc-cuda-conv], [disable lavc CUDA conversions (default is auto)]
+      AS_HELP_STRING([--enable-lavc-cuda-conv], [enable lavc CUDA conversions (default is disable)]
               [Requires: libavcodec CUDA]),
         [lavc_cuda_conv_req=$enableval],
-        [lavc_cuda_conv_req=$build_default]
+        [lavc_cuda_conv_req=no]
 )
 
 if test "$libavcodec_req" != no; then

src/libavcodec/from_lavc_vid_conv_cuda.h

@@ -4,9 +4,12 @@
  * This file contains CUDA-accelerated conversions from FFmpeg to UltraGrid
  * pixfmts.
  * @sa from_lavc_vid_conv.h
+ * @todo
+ * Consider removal - the actual conversions has not been merged until now
+ * (2025-11), the imnplementation in .cu file is just a stub.
  */
 /*
- * Copyright (c) 2024 CESNET, z. s. p. o.
+ * Copyright (c) 2024-2025 CESNET, zájmové sdružení právnických osob
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without

src/libavcodec/to_lavc_vid_conv_cuda.h

@@ -4,9 +4,12 @@
  * This file contains CUDA-accelerated conversions from UltraGrid to
  FFmpeg pixel formats.
  * @sa to_lavc_vid_conv.h
+ * @todo
+ * Consider removal - the actual conversions has not been merged until now
+ * (2025-11), the imnplementation in .cu file is just a stub.
  */
 /*
- * Copyright (c) 2024 CESNET, z. s. p. o.
+ * Copyright (c) 2024-2025 CESNET, zájmové sdružení právnických osob
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without