[FFmpeg-devel] [PATCH 1/2] avcodec/bsf: add datamosh bitstream filter

[Marcus B Spencer <marcus@marcusspencer.xyz>]

Has an option called "target".

For a positive target, drop the nth keyframe.
For a nonpositive target, allow the first n keyframe(s) and drop the remainder.

Its primary purpose is for datamoshing, but it can also be used for dropping parts of audio.

Signed-off-by: Marcus B Spencer <marcus@marcusspencer.xyz>
---
 libavcodec/bitstream_filters.c |  1 +
 libavcodec/bsf/Makefile        |  1 +
 libavcodec/bsf/datamosh.c      | 88 ++++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+)
 create mode 100644 libavcodec/bsf/datamosh.c

diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
index 12860c332b..cde6090c77 100644
--- a/libavcodec/bitstream_filters.c
+++ b/libavcodec/bitstream_filters.c
@@ -29,6 +29,7 @@ extern const FFBitStreamFilter ff_av1_frame_merge_bsf;
 extern const FFBitStreamFilter ff_av1_frame_split_bsf;
 extern const FFBitStreamFilter ff_av1_metadata_bsf;
 extern const FFBitStreamFilter ff_chomp_bsf;
+extern const FFBitStreamFilter ff_datamosh_bsf;
 extern const FFBitStreamFilter ff_dump_extradata_bsf;
 extern const FFBitStreamFilter ff_dca_core_bsf;
 extern const FFBitStreamFilter ff_dts2pts_bsf;
diff --git a/libavcodec/bsf/Makefile b/libavcodec/bsf/Makefile
index fb70ad0c21..ad3b870d12 100644
--- a/libavcodec/bsf/Makefile
+++ b/libavcodec/bsf/Makefile
@@ -6,6 +6,7 @@ OBJS-$(CONFIG_AV1_FRAME_MERGE_BSF)        += bsf/av1_frame_merge.o
 OBJS-$(CONFIG_AV1_FRAME_SPLIT_BSF)        += bsf/av1_frame_split.o
 OBJS-$(CONFIG_AV1_METADATA_BSF)           += bsf/av1_metadata.o
 OBJS-$(CONFIG_CHOMP_BSF)                  += bsf/chomp.o
+OBJS-$(CONFIG_DATAMOSH_BSF)               += bsf/datamosh.o
 OBJS-$(CONFIG_DCA_CORE_BSF)               += bsf/dca_core.o
 OBJS-$(CONFIG_DTS2PTS_BSF)                += bsf/dts2pts.o
 OBJS-$(CONFIG_DUMP_EXTRADATA_BSF)         += bsf/dump_extradata.o
diff --git a/libavcodec/bsf/datamosh.c b/libavcodec/bsf/datamosh.c
new file mode 100644
index 0000000000..8314a4efc8
--- /dev/null
+++ b/libavcodec/bsf/datamosh.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2024 Marcus B Spencer <marcus@marcusspencer.xyz>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdbool.h>
+
+#include "bsf.h"
+#include "bsf_internal.h"
+
+#include "libavutil/opt.h"
+
+typedef struct {
+    const AVClass *class;
+
+    int target, i;
+} DatamoshContext;
+
+static int datamosh_init(AVBSFContext *ctx)
+{
+    DatamoshContext *s = ctx->priv_data;
+
+    s->i = 0;
+
+    return 0;
+}
+
+static int datamosh(AVBSFContext *ctx, AVPacket *pkt)
+{
+    DatamoshContext *s = ctx->priv_data;
+    bool key;
+    int ret;
+
+    ret = ff_bsf_get_packet_ref(ctx, pkt);
+    if (ret < 0)
+        return ret;
+
+    key = pkt->flags & AV_PKT_FLAG_KEY;
+    if (key)
+        ++s->i;
+
+    if (s->target < 1) {
+        if (s->i <= -s->target)
+            return 0;
+        else if (key) {
+            av_packet_unref(pkt);
+            return AVERROR(EAGAIN);
+        }
+    }
+
+    if (key && s->i == s->target) {
+        av_packet_unref(pkt);
+        return AVERROR(EAGAIN);
+    }
+
+    return 0;
+}
+
+
+#define OFFSET(x) offsetof(DatamoshContext, x)
+#define FLAGS (AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_BSF_PARAM)
+
+static const AVOption options[] = {
+    { "target", NULL, OFFSET(target), AV_OPT_TYPE_INT, { .i64 = 0 }, -INT_MAX, INT_MAX, FLAGS },
+    { NULL },
+};
+
+static const AVClass datamosh_class = {
+    .class_name = "datamosh",
+    .item_name = av_default_item_name,
+    .option = options,
+    .version = LIBAVUTIL_VERSION_INT,
+};
-- 
2.45.0

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