avcodec: add eac3_core bitstream filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Changelog

@@ -50,6 +50,7 @@ version <next>:
 - filter_units bitstream filter
 - AV1 Support through libaom
 - E-AC-3 dependent frames support
+- bitstream filter for extracting E-AC-3 core
 
 
 version 3.4:

doc/bitstream_filters.texi

@@ -75,6 +75,10 @@ the header stored in extradata to the key packets:
 ffmpeg -i INPUT -map 0 -flags:v +global_header -c:v libx264 -bsf:v dump_extra out.ts
 @end example
 
+@section eac3_core
+
+Extract the core from a E-AC-3 stream, dropping extra channels.
+
 @section extract_extradata
 
 Extract the in-band extradata.

libavcodec/Makefile

@@ -1043,6 +1043,7 @@ OBJS-$(CONFIG_AAC_ADTSTOASC_BSF)          += aac_adtstoasc_bsf.o mpeg4audio.o
 OBJS-$(CONFIG_CHOMP_BSF)                  += chomp_bsf.o
 OBJS-$(CONFIG_DUMP_EXTRADATA_BSF)         += dump_extradata_bsf.o
 OBJS-$(CONFIG_DCA_CORE_BSF)               += dca_core_bsf.o
+OBJS-$(CONFIG_EAC3_CORE_BSF)              += eac3_core_bsf.o
 OBJS-$(CONFIG_EXTRACT_EXTRADATA_BSF)      += extract_extradata_bsf.o    \
                                              h2645_parse.o
 OBJS-$(CONFIG_FILTER_UNITS_BSF)           += filter_units_bsf.o

libavcodec/bitstream_filters.c

@@ -28,6 +28,7 @@ extern const AVBitStreamFilter ff_aac_adtstoasc_bsf;
 extern const AVBitStreamFilter ff_chomp_bsf;
 extern const AVBitStreamFilter ff_dump_extradata_bsf;
 extern const AVBitStreamFilter ff_dca_core_bsf;
+extern const AVBitStreamFilter ff_eac3_core_bsf;
 extern const AVBitStreamFilter ff_extract_extradata_bsf;
 extern const AVBitStreamFilter ff_filter_units_bsf;
 extern const AVBitStreamFilter ff_h264_metadata_bsf;

libavcodec/eac3_core_bsf.c

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2018 Paul B Mahol
+ *
+ * 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 "avcodec.h"
+#include "bsf.h"
+#include "get_bits.h"
+#include "ac3_parser_internal.h"
+
+static int eac3_core_filter(AVBSFContext *ctx, AVPacket *pkt)
+{
+    AC3HeaderInfo hdr;
+    GetBitContext gbc;
+    int ret;
+
+    ret = ff_bsf_get_packet_ref(ctx, pkt);
+    if (ret < 0)
+        return ret;
+    ret = init_get_bits8(&gbc, pkt->data, pkt->size);
+    if (ret < 0)
+        goto fail;
+
+    ret = ff_ac3_parse_header(&gbc, &hdr);
+    if (ret < 0) {
+        ret = AVERROR_INVALIDDATA;
+        goto fail;
+    }
+
+    if (hdr.frame_type == EAC3_FRAME_TYPE_INDEPENDENT ||
+        hdr.frame_type == EAC3_FRAME_TYPE_AC3_CONVERT) {
+        pkt->size = FFMIN(hdr.frame_size, pkt->size);
+    } else if (hdr.frame_type == EAC3_FRAME_TYPE_DEPENDENT && pkt->size > hdr.frame_size) {
+        AC3HeaderInfo hdr2;
+
+        ret = init_get_bits8(&gbc, pkt->data + hdr.frame_size, pkt->size - hdr.frame_size);
+        if (ret < 0)
+            goto fail;
+
+        ret = ff_ac3_parse_header(&gbc, &hdr2);
+        if (ret < 0) {
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
+
+        if (hdr2.frame_type == EAC3_FRAME_TYPE_INDEPENDENT ||
+            hdr2.frame_type == EAC3_FRAME_TYPE_AC3_CONVERT) {
+            pkt->size -= hdr.frame_size;
+            pkt->data += hdr.frame_size;
+        } else {
+            pkt->size = 0;
+        }
+    } else {
+        pkt->size = 0;
+    }
+
+    return 0;
+fail:
+    av_packet_unref(pkt);
+    return ret;
+}
+
+static const enum AVCodecID codec_ids[] = {
+    AV_CODEC_ID_EAC3, AV_CODEC_ID_NONE,
+};
+
+const AVBitStreamFilter ff_eac3_core_bsf = {
+    .name      = "eac3_core",
+    .filter    = eac3_core_filter,
+    .codec_ids = codec_ids,
+};