On 3/4/20, James Almer <jamr...@gmail.com> wrote:
> On 3/4/2020 7:26 PM, Paul B Mahol wrote:
>> Signed-off-by: Paul B Mahol <one...@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.
That is over complication for simple parsing like here.
Every raw packet have exact frame size set in bitstream.
>
>> + 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;
>>
>
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