Re: [FFmpeg-devel] [PATCH 2/2] avformat/lc3: Add file format for LC3/LC3plus transport

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Antoine Soulier via ffmpeg-devel:
> A file format is described in Bluetooth SIG LC3 and ETSI TS 103 634, for
> test purpose. This is the format implemented here.
> 
> Signed-off-by: Antoine Soulier <asoulier@google.com>
> ---
>  Changelog                |   1 +
>  doc/muxers.texi          |   6 ++
>  libavformat/Makefile     |   2 +
>  libavformat/allformats.c |   2 +
>  libavformat/lc3dec.c     | 135 +++++++++++++++++++++++++++++++++++++++
>  libavformat/lc3enc.c     | 102 +++++++++++++++++++++++++++++
>  6 files changed, 248 insertions(+)
>  create mode 100644 libavformat/lc3dec.c
>  create mode 100644 libavformat/lc3enc.c
> 
> diff --git a/Changelog b/Changelog
> index 83a4cf7888..08c200a41d 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -2,6 +2,7 @@ Entries are sorted chronologically from oldest to youngest within each release,
>  releases are sorted from youngest to oldest.
>  
>  version <next>:
> +- LC3/LC3plus demuxer and muxer
>  - LC3/LC3plus decoding/encoding using external library liblc3
>  
>  
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index a10a8e216f..9687746c30 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -2612,6 +2612,12 @@ WebDAV server every second:
>  ffmpeg -f x11grab -framerate 1 -i :0.0 -q:v 6 -update 1 -protocol_opts method=PUT http://example.com/desktop.jpg
>  @end example
>  
> +@section lc3
> +Bluetooth SIG Low Complexity Communication Codec audio (LC3), or
> +ETSI TS 103 634 Low Complexity Communication Codec plus (LC3plus).
> +
> +This muxer accepts a single @code{lc3} audio stream.
> +
>  @section matroska
>  
>  Matroska container muxer.
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 44aa485029..4961c42852 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -332,6 +332,8 @@ OBJS-$(CONFIG_KVAG_DEMUXER)              += kvag.o
>  OBJS-$(CONFIG_KVAG_MUXER)                += kvag.o rawenc.o
>  OBJS-$(CONFIG_LAF_DEMUXER)               += lafdec.o
>  OBJS-$(CONFIG_LATM_MUXER)                += latmenc.o rawenc.o
> +OBJS-$(CONFIG_LC3_DEMUXER)               += lc3dec.o
> +OBJS-$(CONFIG_LC3_MUXER)                 += lc3enc.o
>  OBJS-$(CONFIG_LMLM4_DEMUXER)             += lmlm4.o
>  OBJS-$(CONFIG_LOAS_DEMUXER)              += loasdec.o rawdec.o
>  OBJS-$(CONFIG_LUODAT_DEMUXER)            += luodatdec.o
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index 9df42bb87a..0b36a7c3eb 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -252,6 +252,8 @@ extern const FFInputFormat  ff_kvag_demuxer;
>  extern const FFOutputFormat ff_kvag_muxer;
>  extern const FFInputFormat  ff_laf_demuxer;
>  extern const FFOutputFormat ff_latm_muxer;
> +extern const FFInputFormat  ff_lc3_demuxer;
> +extern const FFOutputFormat ff_lc3_muxer;
>  extern const FFInputFormat  ff_lmlm4_demuxer;
>  extern const FFInputFormat  ff_loas_demuxer;
>  extern const FFInputFormat  ff_luodat_demuxer;
> diff --git a/libavformat/lc3dec.c b/libavformat/lc3dec.c
> new file mode 100644
> index 0000000000..9ca9825f1b
> --- /dev/null
> +++ b/libavformat/lc3dec.c
> @@ -0,0 +1,135 @@
> +/*
> + * LC3 demuxer
> + * Copyright (C) 2024  Antoine Soulier <asoulier@google.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
> + * Based on the file format specified by :
> + *
> + * - Bluetooth SIG - Low Complexity Communication Codec Test Suite
> + *   https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=502301
> + *   3.2.8.2 Reference LC3 Codec Bitstream Format
> + *
> + * - ETSI TI 103 634 V1.4.1 - Low Complexity Communication Codec plus
> + *   https://www.etsi.org/deliver/etsi_ts/103600_103699/103634/01.04.01_60/ts_103634v010401p.pdf
> + *   LC3plus conformance script package
> + */
> +
> +#include "libavcodec/packet.h"
> +#include "libavutil/intreadwrite.h"
> +
> +#include "avformat.h"
> +#include "avio.h"
> +#include "demux.h"
> +#include "internal.h"
> +
> +typedef struct LC3DemuxContext {
> +    int frame_samples;
> +    int64_t position;
> +    int64_t length;
> +} LC3DemuxContext;
> +
> +static int lc3_read_header(AVFormatContext *s)
> +{
> +    LC3DemuxContext *lc3 = s->priv_data;
> +    AVStream *st = NULL;
> +    uint16_t tag, hdr_size;
> +    uint16_t frame_us;
> +    uint32_t length;
> +    int ep_mode, hr_mode;
> +    int srate_hz, channels, bit_rate;
> +    int num_extra_params, ret;
> +
> +    tag = avio_rb16(s->pb);
> +    hdr_size = avio_rl16(s->pb);
> +
> +    if (tag != 0x1ccc || hdr_size < 9 * sizeof(uint16_t))
> +        return AVERROR_INVALIDDATA;
> +
> +    num_extra_params = hdr_size / sizeof(uint16_t) - 9;
> +
> +    srate_hz = avio_rl16(s->pb) * 100;
> +    bit_rate = avio_rl16(s->pb) * 100;
> +    channels = avio_rl16(s->pb);
> +    frame_us = avio_rl16(s->pb) * 10;

There is nothing that guarantees that the RHS will fit into an uint16_t.
Is there a reason why you are using a more precise timebase for the
extradata than the container format?

> +    ep_mode  = avio_rl16(s->pb) != 0;
> +    length   = avio_rl32(s->pb);
> +    hr_mode  = num_extra_params >= 1 && avio_rl16(s->pb);
> +
> +    st = avformat_new_stream(s, NULL);
> +    if (!st)
> +        return AVERROR(ENOMEM);
> +
> +    avpriv_set_pts_info(st, 32, 1, srate_hz);

Why 32? This format provides no timestamps, so it makes no sense for
them to be wrapped.

> +    st->duration = length;
> +
> +    st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
> +    st->codecpar->codec_id = AV_CODEC_ID_LC3;
> +    st->codecpar->sample_rate = srate_hz;
> +    st->codecpar->bit_rate = bit_rate;
> +    st->codecpar->ch_layout.nb_channels = channels;
> +
> +    if ((ret = ff_alloc_extradata(st->codecpar, 6)) < 0) {
> +        av_log(s, AV_LOG_ERROR, "Could not allocate extradata\n");

Pointless logmessage

> +        return ret;
> +    }
> +
> +    AV_WL16(st->codecpar->extradata + 0, frame_us);
> +    AV_WL16(st->codecpar->extradata + 2, ep_mode);
> +    AV_WL16(st->codecpar->extradata + 4, hr_mode);
> +
> +    lc3->frame_samples = av_rescale(frame_us, srate_hz, 1000*1000);
> +
> +    lc3->position = 0;
> +    lc3->length = st->duration +
> +        av_rescale(frame_us == 7500 ? 4000 : 2500, srate_hz, 1000*1000);
> +
> +    return 0;
> +}
> +
> +static int lc3_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    LC3DemuxContext *lc3 = s->priv_data;
> +    AVIOContext *pb = s->pb;
> +    int ret;
> +
> +    ret = av_get_packet(s->pb, pkt, avio_rl16(pb));
> +    if (ret < 0)
> +        return ret;
> +
> +    pkt->duration = lc3->frame_samples;
> +    lc3->position += lc3->frame_samples;
> +    if (lc3->position > lc3->length) {
> +        pkt->duration -= lc3->position - lc3->length;
> +        lc3->position = lc3->length;
> +    }
> +
> +    return 0;
> +}
> +
> +const FFInputFormat ff_lc3_demuxer = {
> +    .p.name         = "lc3",
> +    .p.long_name    = NULL_IF_CONFIG_SMALL("LC3 (Low Complexity Communication Codec)"),
> +    .p.extensions   = "lc3",
> +    .p.flags        = AVFMT_NOBINSEARCH | AVFMT_NOGENSEARCH | AVFMT_NO_BYTE_SEEK | AVFMT_NOTIMESTAMPS,
> +    .priv_data_size = sizeof(LC3DemuxContext),
> +    .read_header    = lc3_read_header,
> +    .read_packet    = lc3_read_packet,
> +};
> diff --git a/libavformat/lc3enc.c b/libavformat/lc3enc.c
> new file mode 100644
> index 0000000000..a7e3e3f4f7
> --- /dev/null
> +++ b/libavformat/lc3enc.c
> @@ -0,0 +1,102 @@
> +/*
> + * LC3 muxer
> + * Copyright (C) 2024  Antoine Soulier <asoulier@google.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
> + * Based on the file format specified by :
> + *
> + * - Bluetooth SIG - Low Complexity Communication Codec Test Suite
> + *   https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=502301
> + *   3.2.8.2 Reference LC3 Codec Bitstream Format
> + *
> + * - ETSI TI 103 634 V1.4.1 - Low Complexity Communication Codec plus
> + *   https://www.etsi.org/deliver/etsi_ts/103600_103699/103634/01.04.01_60/ts_103634v010401p.pdf
> + *   LC3plus conformance script package
> + */
> +
> +#include "libavutil/intreadwrite.h"
> +
> +#include "avformat.h"
> +#include "avio.h"
> +#include "mux.h"
> +#include "internal.h"
> +
> +static av_cold int lc3_init(AVFormatContext *s)
> +{
> +    if (s->nb_streams != 1) {
> +        av_log(s, AV_LOG_ERROR, "This muxer only supports a single stream.\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    return 0;
> +}
> +
> +static int lc3_write_header(AVFormatContext *s)
> +{
> +    AVStream *st = s->streams[0];
> +    int channels = st->codecpar->ch_layout.nb_channels;
> +    int srate_hz = st->codecpar->sample_rate;
> +    int bit_rate = st->codecpar->bit_rate;
> +    uint16_t frame_us = 10000;
> +    int ep_mode = 0, hr_mode = 0;
> +    uint32_t nb_samples = av_rescale_q(
> +        st->duration, st->time_base, (AVRational){ 1, srate_hz });
> +
> +    if (st->codecpar->extradata_size >= 2)
> +        frame_us = AV_RL16(st->codecpar->extradata + 0);
> +
> +    if (st->codecpar->extradata_size >= 6) {
> +        ep_mode = AV_RL16(st->codecpar->extradata + 2);
> +        hr_mode = AV_RL16(st->codecpar->extradata + 4);
> +    }

Given that this is not an established format, we can simply demand that
extradata_size has to be >= 6.

> +
> +    avio_wb16(s->pb, 0x1ccc);
> +    avio_wl16(s->pb, (9 + hr_mode) * sizeof(uint16_t));
> +    avio_wl16(s->pb, srate_hz / 100);
> +    avio_wl16(s->pb, bit_rate / 100);
> +    avio_wl16(s->pb, channels);
> +    avio_wl16(s->pb, frame_us / 10);
> +    avio_wl16(s->pb, ep_mode);
> +    avio_wl32(s->pb, nb_samples);
> +    if (hr_mode)
> +        avio_wl16(s->pb, hr_mode);
> +
> +    return 0;
> +}
> +
> +static int lc3_write_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    avio_wl16(s->pb, pkt->size);
> +    avio_write(s->pb, pkt->data, pkt->size);
> +    return 0;
> +}
> +
> +const FFOutputFormat ff_lc3_muxer = {
> +    .p.name        = "lc3",
> +    .p.long_name   = NULL_IF_CONFIG_SMALL("LC3 (Low Complexity Communication Codec)"),
> +    .p.extensions  = "lc3",
> +    .p.audio_codec = AV_CODEC_ID_LC3,
> +    .p.video_codec = AV_CODEC_ID_NONE,
> +    .p.flags       = AVFMT_NOTIMESTAMPS,
> +    .init          = lc3_init,
> +    .write_header  = lc3_write_header,
> +    .write_packet  = lc3_write_packet,
> +};

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