[FFmpeg-devel] [PATCH 2/2] avcodec: add eac3_core bitstream filter

[James Almer]

On 3/28/2018 4:00 PM, Paul B Mahol wrote:
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  doc/bitstream_filters.texi     |  4 +++
>  libavcodec/Makefile            |  1 +
>  libavcodec/bitstream_filters.c |  1 +
>  libavcodec/eac3_core_bsf.c     | 80 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 86 insertions(+)
>  create mode 100644 libavcodec/eac3_core_bsf.c
> 
> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
> index 982e3edac8..7322af6550 100644
> --- a/doc/bitstream_filters.texi
> +++ b/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
>  
> + at section eac3_core
> +
> +Extract the core from a E-AC-3 stream, dropping extra channels.
> +
>  @section extract_extradata
>  
>  Extract the in-band extradata.
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index aaef6c3ab8..8220ad855d 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -1041,6 +1041,7 @@ 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
> diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
> index 12211225bb..18b698a85f 100644
> --- a/libavcodec/bitstream_filters.c
> +++ b/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;
> diff --git a/libavcodec/eac3_core_bsf.c b/libavcodec/eac3_core_bsf.c
> new file mode 100644
> index 0000000000..85feb2583b
> --- /dev/null
> +++ b/libavcodec/eac3_core_bsf.c
> @@ -0,0 +1,80 @@
> +/*
> + * 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 "libavutil/mem.h"

Why?

> +#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)
> +        return ret;

av_packet_unref(pkt);

Same with every other failure below, so maybe doing a goto fail would be
easier.

> +
> +    ret = ff_ac3_parse_header(&gbc, &hdr);
> +    if (ret < 0)
> +        return AVERROR_INVALIDDATA;
> +
> +    if (hdr.frame_type == EAC3_FRAME_TYPE_INDEPENDENT ||
> +        hdr.frame_type == EAC3_FRAME_TYPE_AC3_CONVERT) {
> +        pkt->size = hdr.frame_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)
> +            return ret;
> +
> +        ret = ff_ac3_parse_header(&gbc, &hdr2);
> +        if (ret < 0)
> +            return AVERROR_INVALIDDATA;
> +
> +        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;
> +}
> +
> +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,
> +};
>