lavc: deprecate img_get_alpha_info().

It's never been touched or used in any way since it was added in 2003
and only works for PIX_FMT_PAL8, which makes me conclude that nobody's
ever used it.

libavcodec/avcodec.h

@@ -3500,6 +3500,7 @@ int avcodec_get_pix_fmt_loss(enum PixelFormat dst_pix_fmt, enum PixelFormat src_
 enum PixelFormat avcodec_find_best_pix_fmt(int64_t pix_fmt_mask, enum PixelFormat src_pix_fmt,
                               int has_alpha, int *loss_ptr);
 
+#if FF_API_GET_ALPHA_INFO
 #define FF_ALPHA_TRANSP       0x0001 /* image has some totally transparent pixels */
 #define FF_ALPHA_SEMI_TRANSP  0x0002 /* image has some transparent pixels */
 
@@ -3507,8 +3508,10 @@ enum PixelFormat avcodec_find_best_pix_fmt(int64_t pix_fmt_mask, enum PixelForma
  * Tell if an image really has transparent alpha values.
  * @return ored mask of FF_ALPHA_xxx constants
  */
+attribute_deprecated
 int img_get_alpha_info(const AVPicture *src,
                        enum PixelFormat pix_fmt, int width, int height);
+#endif
 
 /* deinterlace a picture */
 /* deinterlace - if not supported return -1 */

libavcodec/imgconvert.c

@@ -862,6 +862,7 @@ int av_picture_pad(AVPicture *dst, const AVPicture *src, int height, int width,
     return 0;
 }
 
+#if FF_API_GET_ALPHA_INFO
 /* NOTE: we scan all the pixels to have an exact information */
 static int get_alpha_info_pal8(const AVPicture *src, int width, int height)
 {
@@ -908,6 +909,7 @@ int img_get_alpha_info(const AVPicture *src,
     }
     return ret;
 }
+#endif
 
 #if !(HAVE_MMX && HAVE_YASM)
 /* filter parameters: [-1 4 2 4 -1] // 8 */

libavcodec/version.h

@@ -98,5 +98,8 @@
 #ifndef FF_API_MJPEG_GLOBAL_OPTS
 #define FF_API_MJPEG_GLOBAL_OPTS (LIBAVCODEC_VERSION_MAJOR < 54)
 #endif
+#ifndef FF_API_GET_ALPHA_INFO
+#define FF_API_GET_ALPHA_INFO    (LIBAVCODEC_VERSION_MAJOR < 54)
+#endif
 
 #endif /* AVCODEC_VERSION_H */