lavc/pgs_frame_merge_bsf: add bsf to merge PGS segments

Required to remux m2ts to mkv
Minor changes and porting to FFBitStreamFilter done by the committer.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

6 files changed, 203 insertions, 1 deletions

diff --git a/Changelog b/Changelog
index 9eca714bbd..4d42a0f681 100644
--- a/Changelog
+++ b/Changelog
@@ -15,6 +15,7 @@ version 5.1:
 - colorchart video source filter
 - blurdetect filter
 - multiply video filter
+- PGS subtitle frame merge bitstream filter
 
 
 version 5.0:
diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
index fc2c71fc12..50c95f035d 100644
--- a/doc/bitstream_filters.texi
+++ b/doc/bitstream_filters.texi
@@ -695,6 +695,14 @@ for NTSC frame rate using the @option{frame_rate} option.
 ffmpeg -f lavfi -i sine=r=48000:d=1 -c pcm_s16le -bsf pcm_rechunk=r=30000/1001 -f framecrc -
 @end example
 
+@section pgs_frame_merge
+
+Merge a sequence of PGS Subtitle segments ending with an "end of display set"
+segment into a single packet.
+
+This is required by some containers that support PGS subtitles
+(muxer @code{matroska}).
+
 @section prores_metadata
 
 Modify color property metadata embedded in prores stream.
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 1b60e0e1d4..38425d2f22 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -1196,6 +1196,7 @@ OBJS-$(CONFIG_NOISE_BSF)                  += noise_bsf.o
 OBJS-$(CONFIG_NULL_BSF)                   += null_bsf.o
 OBJS-$(CONFIG_OPUS_METADATA_BSF)          += opus_metadata_bsf.o
 OBJS-$(CONFIG_PCM_RECHUNK_BSF)            += pcm_rechunk_bsf.o
+OBJS-$(CONFIG_PGS_FRAME_MERGE_BSF)        += pgs_frame_merge_bsf.o
 OBJS-$(CONFIG_PRORES_METADATA_BSF)        += prores_metadata_bsf.o
 OBJS-$(CONFIG_REMOVE_EXTRADATA_BSF)       += remove_extradata_bsf.o av1_parse.o
 OBJS-$(CONFIG_SETTS_BSF)                  += setts_bsf.o
diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
index f117bc0e17..444423ae93 100644
--- a/libavcodec/bitstream_filters.c
+++ b/libavcodec/bitstream_filters.c
@@ -52,6 +52,7 @@ extern const FFBitStreamFilter ff_noise_bsf;
 extern const FFBitStreamFilter ff_null_bsf;
 extern const FFBitStreamFilter ff_opus_metadata_bsf;
 extern const FFBitStreamFilter ff_pcm_rechunk_bsf;
+extern const FFBitStreamFilter ff_pgs_frame_merge_bsf;
 extern const FFBitStreamFilter ff_prores_metadata_bsf;
 extern const FFBitStreamFilter ff_remove_extradata_bsf;
 extern const FFBitStreamFilter ff_setts_bsf;
diff --git a/libavcodec/pgs_frame_merge_bsf.c b/libavcodec/pgs_frame_merge_bsf.c
new file mode 100644
index 0000000000..bcd8945335
--- /dev/null
+++ b/libavcodec/pgs_frame_merge_bsf.c
@@ -0,0 +1,191 @@
+/*
+ * Copyright (c) 2020 John Stebbins <jstebbins.hb@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
+ * This bitstream filter merges PGS subtitle packets containing incomplete
+ * set of segments into a single packet
+ *
+ * Packets already containing a complete set of segments will be passed through
+ * unchanged.
+ */
+
+#include "libavutil/attributes.h"
+#include "libavutil/intreadwrite.h"
+#include "libavutil/log.h"
+#include "bsf.h"
+#include "bsf_internal.h"
+
+enum PGSSegmentType {
+    PALETTE_SEGMENT         = 0x14,
+    OBJECT_SEGMENT          = 0x15,
+    PRESENTATION_SEGMENT    = 0x16,
+    WINDOW_SEGMENT          = 0x17,
+    END_DISPLAY_SET_SEGMENT = 0x80,
+};
+
+typedef struct PGSMergeContext {
+    AVPacket *buffer_pkt, *in;
+    int presentation_found;
+    int pkt_flags;
+} PGSMergeContext;
+
+static av_cold void frame_merge_flush(AVBSFContext *bsf)
+{
+    PGSMergeContext *ctx = bsf->priv_data;
+
+    ctx->presentation_found = ctx->pkt_flags = 0;
+    av_packet_unref(ctx->in);
+    av_packet_unref(ctx->buffer_pkt);
+}
+
+static int frame_merge_output(PGSMergeContext *ctx, AVPacket *dst, AVPacket *src)
+{
+    if (!ctx->presentation_found)
+        ctx->pkt_flags |= AV_PKT_FLAG_CORRUPT;
+    ctx->presentation_found = 0;
+    src->flags    |= ctx->pkt_flags;
+    ctx->pkt_flags = 0;
+    av_packet_move_ref(dst, src);
+    return 0;
+}
+
+static int frame_merge_filter(AVBSFContext *bsf, AVPacket *out)
+{
+    PGSMergeContext *ctx = bsf->priv_data;
+    AVPacket *in = ctx->in, *pkt = ctx->buffer_pkt;
+    int ret, size, pos, display = 0, presentation = 0;
+    unsigned int i;
+
+    if (!in->data) {
+        ret = ff_bsf_get_packet_ref(bsf, in);
+        if (ret == AVERROR_EOF && pkt->data) {
+            // Output remaining data
+            ctx->pkt_flags |= AV_PKT_FLAG_CORRUPT;
+            return frame_merge_output(ctx, out, pkt);
+        }
+        if (ret < 0)
+            return ret;
+    }
+    if (!in->size) {
+        av_packet_unref(in);
+        return AVERROR(EAGAIN);
+    }
+    in->flags &= ~AV_PKT_FLAG_KEY; // Will be detected in the stream
+
+    // Validate packet data and find display_end segment
+    size = in->size;
+    i = 0;
+    while (i + 3 <= in->size) {
+        uint8_t segment_type = in->data[i];
+        int     segment_len  = AV_RB16(in->data + i + 1) + 3;
+
+        if (i + segment_len > in->size)
+            break; // Invalid, segments can't span packets
+        if (segment_type == PRESENTATION_SEGMENT && ctx->presentation_found)
+            break; // Invalid, there can be only one
+        if (segment_type == PRESENTATION_SEGMENT) {
+            uint8_t state;
+            if (segment_len < 11)
+                break; // Invalid presentation segment length
+            ctx->presentation_found = presentation = 1;
+            state = in->data[i + 10] & 0xc0;
+            if (state)
+                ctx->pkt_flags |= AV_PKT_FLAG_KEY;
+            else
+                ctx->pkt_flags &= ~AV_PKT_FLAG_KEY;
+        }
+        i += segment_len;
+        if (segment_type == END_DISPLAY_SET_SEGMENT) {
+            size    = i;
+            display = 1;
+            break;
+        }
+    }
+    if (display && pkt->size == 0 && size == in->size) // passthrough
+        return frame_merge_output(ctx, out, in);
+    if (!display && i != in->size) {
+        av_log(bsf, AV_LOG_WARNING, "Failed to parse PGS segments.\n");
+        // force output what we have
+        size    = in->size;
+        display = 1;
+        ctx->pkt_flags |= AV_PKT_FLAG_CORRUPT;
+    }
+
+    if (presentation) {
+        ret = av_packet_copy_props(pkt, in);
+        if (ret < 0)
+            goto fail;
+    }
+    pos = pkt->size;
+    ret = av_grow_packet(pkt, size);
+    if (ret < 0)
+        goto fail;
+    memcpy(pkt->data + pos, in->data, size);
+
+    if (size == in->size)
+        av_packet_unref(in);
+    else {
+        in->data += size;
+        in->size -= size;
+    }
+
+    if (display)
+        return frame_merge_output(ctx, out, pkt);
+    return AVERROR(EAGAIN);
+
+fail:
+    frame_merge_flush(bsf);
+    return ret;
+}
+
+static av_cold int frame_merge_init(AVBSFContext *bsf)
+{
+    PGSMergeContext *ctx = bsf->priv_data;
+
+    ctx->in  = av_packet_alloc();
+    ctx->buffer_pkt = av_packet_alloc();
+    if (!ctx->in || !ctx->buffer_pkt)
+        return AVERROR(ENOMEM);
+
+    return 0;
+}
+
+static av_cold void frame_merge_close(AVBSFContext *bsf)
+{
+    PGSMergeContext *ctx = bsf->priv_data;
+
+    av_packet_free(&ctx->in);
+    av_packet_free(&ctx->buffer_pkt);
+}
+
+static const enum AVCodecID frame_merge_codec_ids[] = {
+    AV_CODEC_ID_HDMV_PGS_SUBTITLE, AV_CODEC_ID_NONE,
+};
+
+const FFBitStreamFilter ff_pgs_frame_merge_bsf = {
+    .p.name         = "pgs_frame_merge",
+    .p.codec_ids    = frame_merge_codec_ids,
+    .priv_data_size = sizeof(PGSMergeContext),
+    .init           = frame_merge_init,
+    .flush          = frame_merge_flush,
+    .close          = frame_merge_close,
+    .filter         = frame_merge_filter,
+};
diff --git a/libavcodec/version.h b/libavcodec/version.h
index 735c8b813c..87b7284a95 100644
--- a/libavcodec/version.h
+++ b/libavcodec/version.h
@@ -29,7 +29,7 @@
 
 #include "version_major.h"
 
-#define LIBAVCODEC_VERSION_MINOR  27
+#define LIBAVCODEC_VERSION_MINOR  28
 #define LIBAVCODEC_VERSION_MICRO 100
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \