[FFmpeg-devel] [PATCH 2/3] avformat: add raw AC-4 demuxer

[James Almer]

On 3/4/2020 7:26 PM, Paul B Mahol wrote:
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  libavformat/Makefile     |   1 +
>  libavformat/ac4dec.c     | 104 +++++++++++++++++++++++++++++++++++++++
>  libavformat/allformats.c |   1 +
>  3 files changed, 106 insertions(+)
>  create mode 100644 libavformat/ac4dec.c
> 
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index e0681058a2..b4e8d20e65 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -70,6 +70,7 @@ OBJS-$(CONFIG_AA_DEMUXER)                += aadec.o
>  OBJS-$(CONFIG_AAC_DEMUXER)               += aacdec.o apetag.o img2.o rawdec.o
>  OBJS-$(CONFIG_AC3_DEMUXER)               += ac3dec.o rawdec.o
>  OBJS-$(CONFIG_AC3_MUXER)                 += rawenc.o
> +OBJS-$(CONFIG_AC4_DEMUXER)               += ac4dec.o
>  OBJS-$(CONFIG_ACM_DEMUXER)               += acm.o rawdec.o
>  OBJS-$(CONFIG_ACT_DEMUXER)               += act.o
>  OBJS-$(CONFIG_ADF_DEMUXER)               += bintext.o sauce.o
> diff --git a/libavformat/ac4dec.c b/libavformat/ac4dec.c
> new file mode 100644
> index 0000000000..8c6e539409
> --- /dev/null
> +++ b/libavformat/ac4dec.c
> @@ -0,0 +1,104 @@
> +/*
> + * RAW AC-4 demuxer
> + * Copyright (c) 2019 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 "libavutil/avassert.h"
> +#include "libavutil/crc.h"
> +#include "avformat.h"
> +#include "rawdec.h"
> +
> +static int ac4_probe(const AVProbeData *p)
> +{
> +    const uint8_t *buf = p->buf;
> +    int left = p->buf_size;
> +    int max_frames = 0;
> +
> +    while (left > 7) {
> +        int size;
> +
> +        if (buf[0] == 0xAC &&
> +            (buf[1] == 0x40 ||
> +             buf[1] == 0x41)) {
> +            size = (buf[2] << 8) | buf[3];
> +            if (size == 0xFFFF)
> +                size = 3 + (buf[4] << 16) | (buf[5] << 8) | buf[6];
> +            size += 4;
> +            if (buf[1] == 0x41)
> +                size += 2;
> +            max_frames++;
> +            left -= size;
> +            buf += size;
> +        } else {
> +            break;
> +        }
> +    }
> +
> +    return FFMIN(AVPROBE_SCORE_MAX, max_frames * 7);
> +}
> +
> +static int ac4_read_header(AVFormatContext *s)
> +{
> +    AVStream *st;
> +
> +    st = avformat_new_stream(s, NULL);
> +    if (!st)
> +        return AVERROR(ENOMEM);
> +
> +    st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
> +    st->codecpar->codec_id   = AV_CODEC_ID_AC4;
> +
> +    return 0;
> +}
> +
> +static int ac4_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    AVIOContext *pb = s->pb;
> +    int64_t pos;
> +    uint16_t sync;
> +    int ret, size;
> +
> +    if (avio_feof(s->pb))
> +        return AVERROR_EOF;
> +
> +    pos   = avio_tell(s->pb);
> +    sync = avio_rb16(pb);

If there are sync codes then it sounds like the proper thing to do is,
much like with AC3, writing a trivial parser to assemble frames and then
use ff_raw_audio_read_header() and ff_raw_read_partial_packet() here
instead of custom functions.

> +    size = avio_rb16(pb);
> +    if (size == 0xffff)
> +        size = avio_rb24(pb);
> +
> +    ret = av_get_packet(pb, pkt, size);
> +    pkt->pos = pos;
> +    pkt->stream_index = 0;
> +
> +    if (sync == 0xAC41)
> +        avio_skip(pb, 2);
> +
> +    return ret;
> +}
> +
> +AVInputFormat ff_ac4_demuxer = {
> +    .name           = "ac4",
> +    .long_name      = NULL_IF_CONFIG_SMALL("raw AC-4"),
> +    .read_probe     = ac4_probe,
> +    .read_header    = ac4_read_header,
> +    .read_packet    = ac4_read_packet,
> +    .flags          = AVFMT_GENERIC_INDEX,
> +    .extensions     = "ac4",
> +};
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index 0209bf0e30..d2afcb2bdd 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -33,6 +33,7 @@ extern AVInputFormat  ff_aa_demuxer;
>  extern AVInputFormat  ff_aac_demuxer;
>  extern AVInputFormat  ff_ac3_demuxer;
>  extern AVOutputFormat ff_ac3_muxer;
> +extern AVInputFormat  ff_ac4_demuxer;
>  extern AVInputFormat  ff_acm_demuxer;
>  extern AVInputFormat  ff_act_demuxer;
>  extern AVInputFormat  ff_adf_demuxer;
>