Gyan Doshi:
> ---
> doc/bitstream_filters.texi | 64 ++++++++++++---
> libavcodec/noise_bsf.c | 161 +++++++++++++++++++++++++++++++++----
> tests/fate/matroska.mak | 2 +-
> 3 files changed, 199 insertions(+), 28 deletions(-)
>
> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
> index d10842ae47..46e4869f80 100644
> --- a/doc/bitstream_filters.texi
> +++ b/doc/bitstream_filters.texi
> @@ -534,20 +534,62 @@ 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.
> -@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 an expression whose evaluation per-packet determines how often bytes
> in that
> +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 or
> drop is specified,
> +amount will be set to @var{-1}. See below for accepted variables.
> +@item drop, dropamount
> +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.
Negating the dropamount scale broke all prior usages of it.
> @end table
>
> -The following example applies the modification to every byte but does not
> drop
> -any packets.
> +Both @code{amount} and @code{drop} accept expressions containing the
> following variables:
> +
> +@table @samp
> +@item n
> +The index of the packet, starting from zero.
> +@item tb
> +The timebase for packet timestamps.
> +@item pts
> +Packet presentation timestamp.
> +@item dts
> +Packet decoding timestamp.
> +@item nopts
> +Constant representing AV_NOPTS_VALUE.
> +@item startpts
> +First non-AV_NOPTS_VALUE PTS seen in the stream.
> +@item startdts
> +First non-AV_NOPTS_VALUE DTS seen in the stream.
> +@item duration
> +@itemx d
> +Packet duration, in timebase units.
> +@item pos
> +Packet position in input; may be -1 when unknown or not set.
> +@item size
> +Packet size, in bytes.
> +@item key
> +Whether packet is marked as a keyframe.
> +@item state
> +A pseudo random integer, primarily derived from the content of packet
> payload.
> +@end table
> +
> +@subsection Examples
> +Apply modification to every byte but don't drop any packets.
> +@example
> +ffmpeg -i INPUT -c copy -bsf noise=1 output.mkv
> +@end example
> +
> +Drop every video packet not marked as a keyframe after timestamp 30s but do
> not
> +modify any of the remaining packets.
> +@example
> +ffmpeg -i INPUT -c copy -bsf:v noise=drop='gt(t\,30)*not(key)' output.mkv
> +@end example
> +
> +Drop one second of audio every 10 seconds and add some random noise to the
> rest.
> @example
> -ffmpeg -i INPUT -c copy -bsf noise[=1] output.mkv
> +ffmpeg -i INPUT -c copy -bsf:a
> noise=amount=-1:drop='between(mod(t\,10)\,9\,10)' output.mkv
> @end example
>
> @section null
> diff --git a/libavcodec/noise_bsf.c b/libavcodec/noise_bsf.c
> index 6ebd369633..9d7ef93001 100644
> --- a/libavcodec/noise_bsf.c
> +++ b/libavcodec/noise_bsf.c
> @@ -23,55 +23,182 @@
> #include "bsf.h"
> #include "bsf_internal.h"
>
> +#include "libavutil/avstring.h"
> #include "libavutil/log.h"
> #include "libavutil/opt.h"
> +#include "libavutil/eval.h"
> +
> +static const char *const var_names[] = {
> + "n", /// packet index, starting from zero
> + "tb", /// timebase
> + "pts", /// packet presentation timestamp
> + "dts", /// packet decoding timestamp
> + "nopts", /// AV_NOPTS_VALUE
> + "startpts", /// first seen non-AV_NOPTS_VALUE packet
> timestamp
> + "startdts", /// first seen non-AV_NOPTS_VALUE packet
> timestamp
> + "duration", "d", /// packet duration
> + "pos", /// original position of packet in its
> source
> + "size", /// packet size
> + "key" , /// packet keyframe flag
> + "state", /// random-ish state
> + NULL
> +};
> +
> +enum var_name {
> + VAR_N,
> + VAR_TB,
> + VAR_PTS,
> + VAR_DTS,
> + VAR_NOPTS,
> + VAR_STARTPTS,
> + VAR_STARTDTS,
> + VAR_DURATION, VAR_D,
> + VAR_POS,
> + VAR_SIZE,
> + VAR_KEY,
> + VAR_STATE,
> + VAR_VARS_NB
> +};
>
> typedef struct NoiseContext {
> const AVClass *class;
> - int amount;
> - int dropamount;
> +
> + char *amount_str;
> + char *drop_str;
> +
> + AVExpr *amount_pexpr;
> + AVExpr *drop_pexpr;
> +
> + double var_values[VAR_VARS_NB];
> +
> unsigned int state;
> + unsigned int pkt_idx;
> } 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;
> + int ret;
>
> - if (amount <= 0)
> - return AVERROR(EINVAL);
> + if (!s->amount_str) {
> + s->amount_str = !s->drop_str ? av_strdup("-1") : av_strdup("0");
> + if (!s->amount_str)
> + return AVERROR(ENOMEM);
> + }
> +
> + ret = av_expr_parse(&s->amount_pexpr, s->amount_str,
> + var_names, NULL, NULL, NULL, NULL, 0, ctx);
> + if (ret < 0) {
> + av_log(ctx, AV_LOG_ERROR, "Error in parsing expr for amount: %s\n",
> s->amount_str);
> + return ret;
> + }
> +
> + if (s->drop_str) {
> + ret = av_expr_parse(&s->drop_pexpr, s->drop_str,
> + var_names, NULL, NULL, NULL, NULL, 0, ctx);
> + if (ret < 0) {
> + av_log(ctx, AV_LOG_ERROR, "Error in parsing expr for drop:
> %s\n", s->drop_str);
> + return ret;
> + }
> + }
> +
> + s->var_values[VAR_TB] = ctx->time_base_out.den ?
> av_q2d(ctx->time_base_out) : 0;
> + s->var_values[VAR_NOPTS] = AV_NOPTS_VALUE;
> + s->var_values[VAR_STARTPTS] = AV_NOPTS_VALUE;
> + s->var_values[VAR_STARTDTS] = AV_NOPTS_VALUE;
> + s->var_values[VAR_STATE] = 0;
> +
> + return 0;
> +}
> +
> +static int noise(AVBSFContext *ctx, AVPacket *pkt)
> +{
> + NoiseContext *s = ctx->priv_data;
> + int i, ret, amount, drop;
> + double res;
>
> ret = ff_bsf_get_packet_ref(ctx, pkt);
> if (ret < 0)
> return ret;
>
> - if (s->dropamount > 0 && s->state % s->dropamount == 0) {
> - s->state++;
> + s->var_values[VAR_N] = s->pkt_idx++;
> + s->var_values[VAR_PTS] = pkt->pts;
> + s->var_values[VAR_DTS] = pkt->dts;
> + s->var_values[VAR_DURATION] =
> + s->var_values[VAR_D] = pkt->duration;
> + s->var_values[VAR_SIZE] = pkt->size;
> + s->var_values[VAR_KEY] = !!(pkt->flags & AV_PKT_FLAG_KEY);
> + s->var_values[VAR_POS] = pkt->pos;
> +
> + if (s->var_values[VAR_STARTPTS] == AV_NOPTS_VALUE)
> + s->var_values[VAR_STARTPTS] = pkt->pts;
> +
> + if (s->var_values[VAR_STARTDTS] == AV_NOPTS_VALUE)
> + s->var_values[VAR_STARTDTS] = pkt->dts;
> +
> + res = av_expr_eval(s->amount_pexpr, s->var_values, NULL);
> +
> + if (isnan(res))
> + amount = 0;
> + else if (res < 0)
> + amount = (s->state % 10001 + 1);
> + else
> + amount = (int)res;
> +
> + if (s->drop_str) {
> + res = av_expr_eval(s->drop_pexpr, s->var_values, NULL);
> +
> + if (isnan(res))
> + drop = 0;
> + else if (res < 0)
> + drop = !(s->state % FFABS((int)res));
(int)res is UB if the integral part of res is outside the range of int;
(int)res can be 0 even when res < 0.
> + else
> + drop = !!res;
> + }
> +
> + 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) {
> + s->var_values[VAR_STATE] = ++s->state;
> av_packet_unref(pkt);
> return AVERROR(EAGAIN);
> }
>
> - ret = av_packet_make_writable(pkt);
> - if (ret < 0) {
> - av_packet_unref(pkt);
> - return ret;
> + if (amount) {
> + ret = av_packet_make_writable(pkt);
> + if (ret < 0) {
> + av_packet_unref(pkt);
> + return ret;
> + }
> }
>
> for (i = 0; i < pkt->size; i++) {
> s->state += pkt->data[i] + 1;
> - if (s->state % amount == 0)
> + if (amount && s->state % amount == 0)
> pkt->data[i] = s->state;
> }
>
> + s->var_values[VAR_STATE] = s->state;
> +
> return 0;
> }
>
> +static void noise_close(AVBSFContext *bsf)
> +{
> + NoiseContext *s = bsf->priv_data;
> +
> + av_expr_free(s->amount_pexpr);
> + av_expr_free(s->drop_pexpr);
> + s->amount_pexpr = s->drop_pexpr = NULL;
> +}
> +
> #define OFFSET(x) offsetof(NoiseContext, x)
> #define FLAGS
> (AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_BSF_PARAM)
> static const AVOption options[] = {
> - { "amount", NULL, OFFSET(amount), AV_OPT_TYPE_INT, { .i64 = 0 }, 0,
> INT_MAX, FLAGS },
> - { "dropamount", NULL, OFFSET(dropamount), AV_OPT_TYPE_INT, { .i64 = 0 },
> 0, INT_MAX, FLAGS },
> + { "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 },
> { NULL },
> };
>
> @@ -86,5 +213,7 @@ const AVBitStreamFilter ff_noise_bsf = {
> .name = "noise",
> .priv_data_size = sizeof(NoiseContext),
> .priv_class = &noise_class,
> + .init = noise_init,
> + .close = noise_close,
> .filter = noise,
> };
> diff --git a/tests/fate/matroska.mak b/tests/fate/matroska.mak
> index ca7193a055..b57765280a 100644
> --- a/tests/fate/matroska.mak
> +++ b/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=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:dropamount=-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
>
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