[FFmpeg-devel] [PATCH 1/2] avcodec/noise: don't force non-zero value for amount

[Gyan Doshi]

Currently, the user is forced to accept some noise in
packet payload, even if not requested.
---
 doc/bitstream_filters.texi | 13 +++++--------
 libavcodec/noise_bsf.c     | 21 +++++++++++++++------
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
index d10842ae47..2b84bda1fc 100644
--- a/doc/bitstream_filters.texi
+++ b/doc/bitstream_filters.texi
@@ -534,20 +534,17 @@ container. Can be used for fuzzing or testing error resilience/concealment.
 Parameters:
 @table @option
 @item amount
-A numeral string, whose value is related to how often output bytes will
-be modified. Therefore, values below or equal to 0 are forbidden, and
-the lower the more frequent bytes will be modified, with 1 meaning
-every byte is modified.
+Accepts a positive integer. Lower the value, more frequently bytes will be modified,
+with @var{1} meaning every byte is modified. Default is @var{0}.
 @item dropamount
-A numeral string, whose value is related to how often packets will be dropped.
-Therefore, values below or equal to 0 are forbidden, and the lower the more
-frequent packets will be dropped, with 1 meaning every packet is dropped.
+Accepts a positive integer. Lower the value, more frequently packets will be dropped,
+with @var{1} meaning every packet is dropped. Default is @var{0}.
 @end table
 
 The following example applies the modification to every byte but does not drop
 any packets.
 @example
-ffmpeg -i INPUT -c copy -bsf noise[=1] output.mkv
+ffmpeg -i INPUT -c copy -bsf noise=amount=1 output.mkv
 @end example
 
 @section null
diff --git a/libavcodec/noise_bsf.c b/libavcodec/noise_bsf.c
index 6ebd369633..c1b0203442 100644
--- a/libavcodec/noise_bsf.c
+++ b/libavcodec/noise_bsf.c
@@ -33,20 +33,28 @@ typedef struct NoiseContext {
     unsigned int state;
 } NoiseContext;
 
-static int noise(AVBSFContext *ctx, AVPacket *pkt)
+static int noise_init(AVBSFContext *ctx)
 {
     NoiseContext *s = ctx->priv_data;
-    int amount = s->amount > 0 ? s->amount : (s->state % 10001 + 1);
-    int i, ret;
 
-    if (amount <= 0)
+    if (!s->amount && !s->dropamount) {
+        av_log(ctx, AV_LOG_ERROR, "At least one of amount and dropamount must be set.\n");
         return AVERROR(EINVAL);
+    }
+
+    return 0;
+}
+
+static int noise(AVBSFContext *ctx, AVPacket *pkt)
+{
+    NoiseContext *s = ctx->priv_data;
+    int i, ret;
 
     ret = ff_bsf_get_packet_ref(ctx, pkt);
     if (ret < 0)
         return ret;
 
-    if (s->dropamount > 0 && s->state % s->dropamount == 0) {
+    if (s->dropamount && s->state % s->dropamount == 0) {
         s->state++;
         av_packet_unref(pkt);
         return AVERROR(EAGAIN);
@@ -60,7 +68,7 @@ static int noise(AVBSFContext *ctx, AVPacket *pkt)
 
     for (i = 0; i < pkt->size; i++) {
         s->state += pkt->data[i] + 1;
-        if (s->state % amount == 0)
+        if (s->amount && s->state % s->amount == 0)
             pkt->data[i] = s->state;
     }
 
@@ -86,5 +94,6 @@ const AVBitStreamFilter ff_noise_bsf = {
     .name           = "noise",
     .priv_data_size = sizeof(NoiseContext),
     .priv_class     = &noise_class,
+    .init           = noise_init,
     .filter         = noise,
 };
-- 
2.32.0