lavc: deprecate rate_emu

It's not used anywhere and apparrently hasn't been for a very long time.

libavcodec/avcodec.h

@@ -1208,13 +1208,15 @@ typedef struct AVCodecContext {
      */
     enum PixelFormat pix_fmt;
 
+#if FF_API_RATE_EMU
     /**
      * Frame rate emulation. If not zero, the lower layer (i.e. format handler)
      * has to read frames at native frame rate.
      * - encoding: Set by user.
      * - decoding: unused
      */
-    int rate_emu;
+    attribute_deprecated int rate_emu;
+#endif
 
     /**
      * If non NULL, 'draw_horiz_band' is called by the libavcodec

libavcodec/options.c

@@ -105,7 +105,9 @@ static const AVOption options[]={
 {"extradata_size", NULL, OFFSET(extradata_size), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX},
 {"time_base", NULL, OFFSET(time_base), FF_OPT_TYPE_RATIONAL, DEFAULT, INT_MIN, INT_MAX},
 {"g", "set the group of picture size", OFFSET(gop_size), FF_OPT_TYPE_INT, 12, INT_MIN, INT_MAX, V|E},
+#if FF_API_RATE_EMU
 {"rate_emu", "frame rate emulation", OFFSET(rate_emu), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX},
+#endif
 {"ar", "set audio sampling rate (in Hz)", OFFSET(sample_rate), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX},
 {"ac", "set number of audio channels", OFFSET(channels), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX},
 {"cutoff", "set cutoff bandwidth", OFFSET(cutoff), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX, A|E},

libavcodec/version.h

@@ -74,5 +74,8 @@
 #ifndef FF_API_HURRY_UP
 #define FF_API_HURRY_UP         (LIBAVCODEC_VERSION_MAJOR < 53)
 #endif
+#ifndef FF_API_RATE_EMU
+#define FF_API_RATE_EMU         (LIBAVCODEC_VERSION_MAJOR < 53)
+#endif
 
 #endif /* AVCODEC_VERSION_H */