[FFmpeg-devel] [PATCH] avformat/lc3: Add file format for LC3/LC3plus transport
Stefano Sabatini
stefasab at gmail.com
Mon Apr 8 17:30:51 EEST 2024
On date Saturday 2024-04-06 21:08:19 +0000, ffmpeg-devel Mailing List wrote:
> From: Antoine SOULIER <asoulier at google.com>
>
> A file format is described in Bluetooth SIG LC3 and ETSI TS 103 634, for
> test purpose. This is the format implemented here.
> ---
> Changelog | 1 +
> doc/muxers.texi | 6 ++
> libavformat/Makefile | 2 +
> libavformat/allformats.c | 2 +
> libavformat/lc3dec.c | 173 +++++++++++++++++++++++++++++++++++++++
> libavformat/lc3enc.c | 114 ++++++++++++++++++++++++++
> 6 files changed, 298 insertions(+)
> create mode 100644 libavformat/lc3dec.c
> create mode 100644 libavformat/lc3enc.c
>
> diff --git a/Changelog b/Changelog
> index 18e83b99a1..02ed7831ec 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -4,6 +4,7 @@ releases are sorted from youngest to oldest.
> version <next>:
> - Raw Captions with Time (RCWT) closed caption demuxer
> - LC3/LC3plus decoding/encoding using external library liblc3
> +- LC3/LC3plus demuxer and muxer
>
>
> version 7.0:
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index d8a1f83309..ed4144f6d1 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -2700,6 +2700,12 @@ computer-generated compositions.
>
> This muxer accepts a single audio stream containing PCM data.
>
> + at 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 9981799cc9..027d0cdae5 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 ae925dcf60..305fa46532 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..371e9242d5
> --- /dev/null
> +++ b/libavformat/lc3dec.c
> @@ -0,0 +1,173 @@
> +/*
> + * LC3 demuxer
> + * Copyright (C) 2024 Antoine Soulier <asoulier at 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 end_dts;
> +} LC3DemuxContext;
> +
> +static int lc3_read_probe(const AVProbeData *p)
> +{
> + int frame_us, srate_hz;
> +
> + if (p->buf_size < 12)
> + return 0;
> +
> + if (AV_RB16(p->buf + 0) != 0x1ccc ||
> + AV_RL16(p->buf + 2) < 9 * sizeof(uint16_t))
> + return 0;
> +
> + srate_hz = AV_RL16(p->buf + 4) * 100;
> + if (srate_hz != 8000 && srate_hz != 16000 && srate_hz != 24000 &&
> + srate_hz != 32000 && srate_hz != 48000 && srate_hz != 96000)
> + return 0;
> +
> + frame_us = AV_RL16(p->buf + 10) * 10;
> + if (frame_us != 2500 && frame_us != 5000 &&
> + frame_us != 7500 && frame_us != 10000)
> + return 0;
> +
> + return AVPROBE_SCORE_MAX;
> +}
> +
> +static int lc3_read_header(AVFormatContext *s)
> +{
> + LC3DemuxContext *lc3 = s->priv_data;
> + AVStream *st = NULL;
> + uint16_t tag, hdr_size;
> + uint32_t length;
> + int srate_hz, frame_us, channels, bit_rate;
> + int ep_mode, hr_mode;
> + int num_extra_params;
> + int delay, 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;
> + ep_mode = avio_rl16(s->pb) != 0;
> + length = avio_rl32(s->pb);
> + hr_mode = num_extra_params >= 1 && avio_rl16(s->pb);
> +
> + if (srate_hz != 8000 && srate_hz != 16000 && srate_hz != 24000 &&
> + srate_hz != 32000 && srate_hz != 48000 && srate_hz != 96000) {
> + av_log(s, AV_LOG_ERROR, "Incompatible LC3 sample rate: %d Hz.\n",
> + srate_hz);
> + return AVERROR_INVALIDDATA;
> + }
> +
> + if (frame_us != 2500 && frame_us != 5000 &&
> + frame_us != 7500 && frame_us != 10000) {
> + av_log(s, AV_LOG_ERROR, "Incompatible LC3 frame duration: %.1f ms.\n",
> + frame_us / 1000.f);
> + return AVERROR_INVALIDDATA;
> + }
This data and logic is repeated three times in the code.
To avoid the code duplication I suggest two possible solutions:
1. store an ff_lc3_check_sample_rate() and ff_lc3_check_frame_size()
function in a common lc3.[hc] file and header (see for example caf.*)
2. put the shared utils, muxer, and demuxer in the same module (see
for example codec2.c) with conditional compilation guards
Possibly solution #2 should be simpler.
[...]
Thanks.
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