[FFmpeg-devel] libavcodec: add timer bitstream filter

diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
index 40e8ada..777f4b6 100644
--- a/doc/bitstream_filters.texi
+++ b/doc/bitstream_filters.texi
@@ -629,6 +629,10 @@  codec) with metadata headers.
 
 See also the @ref{mov2textsub} filter.
 
+@section timer
+
+Apply an offset to the PTS/DTS timestamps.
+
 @section trace_headers
 
 Log trace output containing all syntax elements in the coded stream
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index edccd73..0f2770a 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -1096,6 +1096,7 @@  OBJS-$(CONFIG_NULL_BSF)                   += null_bsf.o
 OBJS-$(CONFIG_PRORES_METADATA_BSF)        += prores_metadata_bsf.o
 OBJS-$(CONFIG_REMOVE_EXTRADATA_BSF)       += remove_extradata_bsf.o
 OBJS-$(CONFIG_TEXT2MOVSUB_BSF)            += movsub_bsf.o
+OBJS-$(CONFIG_TIMER_BSF)                  += timer_bsf.o
 OBJS-$(CONFIG_TRACE_HEADERS_BSF)          += trace_headers_bsf.o
 OBJS-$(CONFIG_TRUEHD_CORE_BSF)            += truehd_core_bsf.o mlp_parse.o mlp.o
 OBJS-$(CONFIG_VP9_METADATA_BSF)           += vp9_metadata_bsf.o
diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
index 4630039..be6af05 100644
--- a/libavcodec/bitstream_filters.c
+++ b/libavcodec/bitstream_filters.c
@@ -51,6 +51,7 @@  extern const AVBitStreamFilter ff_null_bsf;
 extern const AVBitStreamFilter ff_prores_metadata_bsf;
 extern const AVBitStreamFilter ff_remove_extradata_bsf;
 extern const AVBitStreamFilter ff_text2movsub_bsf;
+extern const AVBitStreamFilter ff_timer_bsf;
 extern const AVBitStreamFilter ff_trace_headers_bsf;
 extern const AVBitStreamFilter ff_truehd_core_bsf;
 extern const AVBitStreamFilter ff_vp9_metadata_bsf;
diff --git a/libavcodec/timer_bsf.c b/libavcodec/timer_bsf.c
new file mode 100644
index 0000000..3f1c7f6
--- /dev/null
+++ b/libavcodec/timer_bsf.c
@@ -0,0 +1,86 @@ 
+/*
+ * 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
+ */
+
+/**
+ * @file
+ * This bitstream filter applies an offset to the PTS/DTS timestamps.
+ *
+ */
+
+// TODO: Control time wrapping
+// TODO: Instead of using absolute timestamp offsets, use frame numbers
+
+#include "avcodec.h"
+#include "bsf.h"
+
+#include "libavutil/opt.h"
+
+typedef struct TimerContext {
+    const AVClass *class;
+    int offset;
+    int first_debug_done;
+} TimerContext;
+
+static int timer_filter(AVBSFContext *ctx, AVPacket *pkt)
+{
+    int ret;
+    TimerContext *s = ctx->priv_data;
+    int64_t opts,odts;
+
+    ret = ff_bsf_get_packet_ref(ctx, pkt);
+    if (ret < 0)
+        return ret;
+
+    opts = pkt->pts;
+    if (pkt->pts != AV_NOPTS_VALUE) {
+        pkt->pts += s->offset;
+    }
+    odts = pkt->dts;
+    if (pkt->dts != AV_NOPTS_VALUE) {
+        pkt->dts += s->offset;
+    }
+
+    if (!s->first_debug_done) {
+        av_log(ctx, AV_LOG_DEBUG, "Updated PTS/DTS (%"PRId64"/%"PRId64" : %"PRId64"/%"PRId64") with offset:%d\n",
+                pkt->pts, pkt->dts, opts, odts, s->offset );
+    }
+    s->first_debug_done = 1;
+
+    return 0;
+}
+
+#define OFFSET(x) offsetof(TimerContext, x)
+#define FLAGS (AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_SUBTITLE_PARAM|AV_OPT_FLAG_BSF_PARAM)
+static const AVOption options[] = {
+    { "offset", NULL, OFFSET(offset), AV_OPT_TYPE_INT, { .i64 = 0 }, INT_MIN, INT_MAX, FLAGS },
+    { NULL },
+};
+
+static const AVClass timer_class = {
+    .class_name = "timer",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
+const AVBitStreamFilter ff_timer_bsf = {
+    .name           = "timer",
+    .priv_data_size = sizeof(TimerContext),
+    .priv_class     = &timer_class,
+    .filter         = timer_filter,
+};