avcodec: remove avcodec-fast support

The avcodec-fast option, if enabled, sets the AV_CODEC_FLAG2_FAST
option. Using AV_CODEC_FLAG2_FAST can cause use of unsafe code in
avcodec which could lead to crashes.

modules/codec/avcodec/avcodec.c

@@ -118,7 +118,7 @@ vlc_module_begin ()
     add_obsolete_integer( "avcodec-vismv" ) /* removed since 3.0.0 */
     add_obsolete_integer ( "ffmpeg-lowres" ) /* removed since 2.1.0 */
     add_obsolete_bool( "ffmpeg-fast" ) /* removed since 2.1.0 */
-    add_bool( "avcodec-fast", false, FAST_TEXT, FAST_LONGTEXT, false )
+    add_obsolete_bool( "avcodec-fast" ) /* removed since 4.0.0 */
     add_obsolete_integer ( "ffmpeg-skiploopfilter" ) /* removed since 2.1.0 */
     add_integer ( "avcodec-skiploopfilter", 0, SKIPLOOPF_TEXT,
                   SKIPLOOPF_LONGTEXT, false)

modules/codec/avcodec/avcodec.h

@@ -84,10 +84,6 @@ int ffmpeg_OpenCodec( decoder_t *p_dec, AVCodecContext *, const AVCodec * );
     "when there is not enough time. It's useful with low CPU power " \
     "but it can produce distorted pictures.")
 
-#define FAST_TEXT N_("Allow speed tricks")
-#define FAST_LONGTEXT N_( \
-    "Allow non specification compliant speedup tricks. Faster but error-prone.")
-
 #define SKIP_FRAME_TEXT N_("Skip frame (default=0)")
 #define SKIP_FRAME_LONGTEXT N_( \
     "Force skipping of frames to speed up decoding " \

modules/codec/avcodec/video.c

@@ -573,9 +573,6 @@ int InitVideoDec( vlc_object_t *obj )
     else if( i_val == 1 ) p_context->skip_loop_filter = AVDISCARD_NONREF;
     else p_context->skip_loop_filter = AVDISCARD_DEFAULT;
 
-    if( var_CreateGetBool( p_dec, "avcodec-fast" ) )
-        p_context->flags2 |= AV_CODEC_FLAG2_FAST;
-
     /* ***** libavcodec frame skipping ***** */
     p_sys->b_hurry_up = var_CreateGetBool( p_dec, "avcodec-hurry-up" );
     p_sys->b_show_corrupted = var_CreateGetBool( p_dec, "avcodec-corrupted" );