[FFmpeg-devel] [PATCH] Add new MPEG bitstream filter
David Griffiths
david.griffiths at gmail.com
Tue Aug 1 15:22:33 EEST 2017
Given an MPEG1/2 stream, this bitstream filter can be used to modify
the sequence headers. The most common use would be to change the
aspect ration without the need for re-encoding. Some MOD files have
the aspect ratio incorrectly set to 4:3
(see https://en.wikipedia.org/wiki/MOD_and_TOD).
---
doc/bitstream_filters.texi | 21 ++++++++
libavcodec/Makefile | 1 +
libavcodec/bitstream_filters.c | 1 +
libavcodec/mod_mpeg_seq_header_bsf.c | 102 +++++++++++++++++++++++++++++++++++
4 files changed, 125 insertions(+)
create mode 100644 libavcodec/mod_mpeg_seq_header_bsf.c
diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
index 2dffe021f9..c9801f966c 100644
--- a/doc/bitstream_filters.texi
+++ b/doc/bitstream_filters.texi
@@ -186,6 +186,27 @@ ffmpeg -i frame_%d.jpg -c:v copy rotated.avi
Add an MJPEG A header to the bitstream, to enable decoding by
Quicktime.
+ at section mod_mpeg_seq_header
+
+Given an MPEG1/2 stream, this bitstream filter can be used to modify
+the sequence headers. The most common use would be to change the
+aspect ration without the need for re-encoding. Some MOD files have
+the aspect ratio incorrectly set to 4:3 (see
+ at url{https://en.wikipedia.org/wiki/MOD_and_TOD}).
+
+To set widescreen format in a mod file do this:
+
+ at example
+ffmpeg -i in.mod -bsf:v mod_mpeg_seq_header=aspect_ratio=3 -codec copy out.mpeg
+ at end example
+
+ at table @option
+ at item aspect_ratio
+Common values are 2 for 4:3 format and 3 for 16:9 (widescreen).
+ at item frame_rate
+Use 2 for 24 fps and 3 for 25 fps.
+ at end table
+
@anchor{mov2textsub}
@section mov2textsub
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 357fa1a361..e275eb6062 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -1002,6 +1002,7 @@ OBJS-$(CONFIG_TEXT2MOVSUB_BSF) += movsub_bsf.o
OBJS-$(CONFIG_VP9_RAW_REORDER_BSF) += vp9_raw_reorder_bsf.o
OBJS-$(CONFIG_VP9_SUPERFRAME_BSF) += vp9_superframe_bsf.o
OBJS-$(CONFIG_VP9_SUPERFRAME_SPLIT_BSF) += vp9_superframe_split_bsf.o
+OBJS-$(CONFIG_MOD_MPEG_SEQ_HEADER_BSF) += mod_mpeg_seq_header_bsf.o
# thread libraries
OBJS-$(HAVE_LIBC_MSVCRT) += file_open.o
diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
index ce34de640d..dfe46e3e0c 100644
--- a/libavcodec/bitstream_filters.c
+++ b/libavcodec/bitstream_filters.c
@@ -44,6 +44,7 @@ extern const AVBitStreamFilter ff_text2movsub_bsf;
extern const AVBitStreamFilter ff_vp9_raw_reorder_bsf;
extern const AVBitStreamFilter ff_vp9_superframe_bsf;
extern const AVBitStreamFilter ff_vp9_superframe_split_bsf;
+extern const AVBitStreamFilter ff_mod_mpeg_seq_header_bsf;
#include "libavcodec/bsf_list.c"
diff --git a/libavcodec/mod_mpeg_seq_header_bsf.c b/libavcodec/mod_mpeg_seq_header_bsf.c
new file mode 100644
index 0000000000..824197746b
--- /dev/null
+++ b/libavcodec/mod_mpeg_seq_header_bsf.c
@@ -0,0 +1,102 @@
+/*
+ * Modify MPEG Sequence Headers bitstream filter
+ * Copyright (c) 2017 David Griffiths <david.griffiths at gmail.com>
+ *
+ * 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
+ * Modify MPEG Sequence Headers bitstream filter
+ */
+
+#include "avcodec.h"
+#include "bsf.h"
+#include "internal.h"
+
+#include "libavutil/opt.h"
+
+typedef struct ModifySeqHeaderContext {
+ const AVClass *class;
+ int aspect_ratio;
+ int frame_rate;
+ int done_log;
+} ModifySeqHeaderContext;
+
+/**
+ * This filter can be used to modify the sequence headers for aspect ratio
+ * and/or frame rate without the need for transcoding.
+ */
+static int mod_mpeg_seq_header_filter(AVBSFContext *ctx, AVPacket *out)
+{
+ ModifySeqHeaderContext *s = ctx->priv_data;
+ AVPacket *in;
+ int ret;
+
+ ret = ff_bsf_get_packet(ctx, &in);
+ if (ret < 0)
+ return ret;
+
+ if (in->data[0] == 0 && in->data[1] == 0 && in->data[2] == 1 &&
+ in->data[3] == 0xb3) {
+ if (!s->done_log)
+ av_log(ctx, AV_LOG_INFO, "old aspect byte was %x\n", in->data[7]);
+ if (s->aspect_ratio != 0) {
+ in->data[7] = (s->aspect_ratio << 4) | (in->data[7] & 0xf);
+ }
+ if (s->frame_rate != 0) {
+ in->data[7] = s->frame_rate | (in->data[7] & 0xf0);
+ }
+ if (!s->done_log)
+ av_log(ctx, AV_LOG_INFO, "new aspect byte is %x\n", in->data[7]);
+ s->done_log = 1;
+ }
+
+ av_packet_move_ref(out, in);
+ av_packet_free(&in);
+
+ return 0;
+}
+
+static const enum AVCodecID codec_ids[] = {
+ AV_CODEC_ID_MPEG1VIDEO,
+ AV_CODEC_ID_MPEG2VIDEO,
+ AV_CODEC_ID_NONE,
+};
+
+#define OFFSET(x) offsetof(ModifySeqHeaderContext, x)
+static const AVOption options[] = {
+ { "aspect_ratio", NULL, OFFSET(aspect_ratio), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 14 },
+ { "frame_rate", NULL, OFFSET(frame_rate), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 8 },
+ { NULL },
+};
+
+static const AVClass mod_mpeg_seq_header_class = {
+ .class_name = "mod_mpeg_seq_header",
+ .item_name = av_default_item_name,
+ .option = options,
+ .version = LIBAVUTIL_VERSION_INT,
+};
+
+
+const AVBitStreamFilter ff_mod_mpeg_seq_header_bsf = {
+ .name = "mod_mpeg_seq_header",
+ .priv_data_size = sizeof(ModifySeqHeaderContext),
+ .priv_class = &mod_mpeg_seq_header_class,
+ .filter = mod_mpeg_seq_header_filter,
+ .codec_ids = codec_ids,
+};
--
2.13.3
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