avcodec/noise_bsf: restore dropamount for backwards compatibility

doc/bitstream_filters.texi

@@ -538,11 +538,16 @@ Accepts an expression whose evaluation per-packet determines how often bytes in
 packet will be modified. A value below 0 will result in a variable frequency.
 Default is 0 which results in no modification. However, if neither amount nor drop is specified,
 amount will be set to @var{-1}. See below for accepted variables.
-@item drop, dropamount
+@item drop
 Accepts an expression evaluated per-packet whose value determines whether that packet is dropped.
 Evaluation to a positive value results in the packet being dropped. Evaluation to a negative
 value results in a variable chance of it being dropped, roughly inverse in proportion to the magnitude
 of the value. Default is 0 which results in no drops. See below for accepted variables.
+@item dropamount
+Accepts a non-negative integer, which assigns a variable chance of it being dropped, roughly inverse
+in proportion to the value. Default is 0 which results in no drops. This option is kept for backwards
+compatibility and is equivalent to setting drop to a negative value with the same magnitude
+i.e. @code{dropamount=4} is the same as @code{drop=-4}. Ignored if drop is also specified.
 @end table
 
 Both @code{amount} and @code{drop} accept expressions containing the following variables:

libavcodec/noise_bsf.c

@@ -65,6 +65,7 @@ typedef struct NoiseContext {
 
     char *amount_str;
     char *drop_str;
+    int dropamount;
 
     AVExpr *amount_pexpr;
     AVExpr *drop_pexpr;
@@ -81,7 +82,7 @@ static int noise_init(AVBSFContext *ctx)
     int ret;
 
     if (!s->amount_str) {
-        s->amount_str = !s->drop_str ? av_strdup("-1") : av_strdup("0");
+        s->amount_str = (!s->drop_str && !s->dropamount) ? av_strdup("-1") : av_strdup("0");
         if (!s->amount_str)
             return AVERROR(ENOMEM);
     }
@@ -93,6 +94,12 @@ static int noise_init(AVBSFContext *ctx)
         return ret;
     }
 
+    if (s->drop_str && s->dropamount) {
+        av_log(ctx, AV_LOG_WARNING, "Both drop '%s' and dropamount=%d set. Ignoring dropamount.\n",
+               s->drop_str, s->dropamount);
+        s->dropamount = 0;
+    }
+
     if (s->drop_str) {
         ret = av_expr_parse(&s->drop_pexpr, s->drop_str,
                             var_names, NULL, NULL, NULL, NULL, 0, ctx);
@@ -114,7 +121,7 @@ static int noise_init(AVBSFContext *ctx)
 static int noise(AVBSFContext *ctx, AVPacket *pkt)
 {
     NoiseContext *s = ctx->priv_data;
-    int i, ret, amount, drop;
+    int i, ret, amount, drop = 0;
     double res;
 
     ret = ff_bsf_get_packet_ref(ctx, pkt);
@@ -156,10 +163,14 @@ static int noise(AVBSFContext *ctx, AVPacket *pkt)
             drop = !!res;
     }
 
+    if(s->dropamount) {
+        drop = !(s->state % s->dropamount);
+    }
+
     av_log(ctx, AV_LOG_VERBOSE, "Stream #%d packet %d pts %"PRId64" - amount %d drop %d\n",
            pkt->stream_index, (unsigned int)s->var_values[VAR_N], pkt->pts, amount, drop);
 
-    if (s->drop_str && drop) {
+    if (drop) {
         s->var_values[VAR_STATE] = ++s->state;
         av_packet_unref(pkt);
         return AVERROR(EAGAIN);
@@ -198,7 +209,7 @@ static void noise_close(AVBSFContext *bsf)
 static const AVOption options[] = {
     { "amount",     NULL, OFFSET(amount_str),     AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, FLAGS },
     { "drop",       NULL, OFFSET(drop_str),       AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, FLAGS },
-    { "dropamount", NULL, OFFSET(drop_str),       AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, FLAGS },
+    { "dropamount", NULL, OFFSET(dropamount),     AV_OPT_TYPE_INT,    { .i64 = 0    }, 0, INT_MAX, FLAGS },
     { NULL },
 };
 

tests/fate/matroska.mak

@@ -88,7 +88,7 @@ FATE_MATROSKA_FFMPEG_FFPROBE-$(call ALLYES, FILE_PROTOCOL MXF_DEMUXER        \
                                             MATROSKA_MUXER MATROSKA_DEMUXER  \
                                             FRAMECRC_MUXER PIPE_PROTOCOL)    \
                                += fate-matroska-mastering-display-metadata
-fate-matroska-mastering-display-metadata: CMD = transcode mxf $(TARGET_SAMPLES)/mxf/Meridian-Apple_ProResProxy-HDR10.mxf matroska "-map 0 -map 0:0 -c:v:0 copy -c:v:1 ffv1 -c:a:0 copy -bsf:a:0 noise=amount=3 -filter:a:1 aresample -c:a:1 pcm_s16be -bsf:a:1 noise=amount=-1:dropamount=-4" "-map 0 -c copy" "" "-show_entries stream_side_data_list:stream=index,codec_name"
+fate-matroska-mastering-display-metadata: CMD = transcode mxf $(TARGET_SAMPLES)/mxf/Meridian-Apple_ProResProxy-HDR10.mxf matroska "-map 0 -map 0:0 -c:v:0 copy -c:v:1 ffv1 -c:a:0 copy -bsf:a:0 noise=amount=3 -filter:a:1 aresample -c:a:1 pcm_s16be -bsf:a:1 noise=amount=-1:drop=-4" "-map 0 -c copy" "" "-show_entries stream_side_data_list:stream=index,codec_name"
 
 # This test tests remuxing annex B H.264 into Matroska. It also tests writing
 # the correct interlaced flags and overriding the sample aspect ratio, leading