avformat/lc3: add file format for LC3/LC3plus transport

A file format is described in Bluetooth SIG LC3 and ETSI TS 103 634, for test purpose.
neoxpert · Apr 15, 2024 · 257bc2a · 257bc2a
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diff --git a/Changelog b/Changelog
@@ -5,6 +5,7 @@ version <next>:
 - Raw Captions with Time (RCWT) closed caption demuxer
 - LC3/LC3plus decoding/encoding using external library liblc3
 - ffmpeg CLI filtergraph chaining
+- LC3/LC3plus demuxer and muxer
 
 
 version 7.0:

diff --git a/doc/muxers.texi b/doc/muxers.texi
@@ -2725,6 +2725,12 @@ games such as "Real War", and "Real War: Rogue States".
 
 This muxer accepts a single @samp{adpcm_ima_ssi} audio stream.
 
+@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 @samp{lc3} audio stream.
+
 @section lrc
 LRC lyrics file format muxer.
 

diff --git 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-$(CONFIG_LC3_DEMUXER)               += lc3.o
+OBJS-$(CONFIG_LC3_MUXER)                 += lc3.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
@@ -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/lc3.c b/libavformat/lc3.c
@@ -0,0 +1,252 @@
+/*
+ * LC3 muxer and 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 "config_components.h"
+
+#include "libavcodec/packet.h"
+#include "libavutil/intreadwrite.h"
+
+#include "avformat.h"
+#include "avio.h"
+#include "demux.h"
+#include "internal.h"
+#include "mux.h"
+
+static int check_frame_length(void *avcl, int srate_hz, int frame_us)
+{
+    if (srate_hz !=  8000 && srate_hz != 16000 && srate_hz != 24000 &&
+        srate_hz != 32000 && srate_hz != 48000 && srate_hz != 96000) {
+        if (avcl)
+            av_log(avcl, AV_LOG_ERROR,
+                   "Invalid LC3 sample rate: %d Hz.\n", srate_hz);
+        return -1;
+    }
+
+    if (frame_us != 2500 && frame_us !=  5000 &&
+        frame_us != 7500 && frame_us != 10000) {
+        if (avcl)
+            av_log(avcl, AV_LOG_ERROR,
+                   "Invalid LC3 frame duration: %.1f ms.\n", frame_us / 1000.f);
+        return -1;
+    }
+
+    return 0;
+}
+
+#if CONFIG_LC3_DEMUXER
+
+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;
+    frame_us = AV_RL16(p->buf + 10) * 10;
+    if (check_frame_length(NULL, srate_hz, frame_us) < 0)
+        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 (check_frame_length(s, srate_hz, frame_us) < 0)
+        return AVERROR_INVALIDDATA;
+
+    st = avformat_new_stream(s, NULL);
+    if (!st)
+        return AVERROR(ENOMEM);
+
+    avpriv_set_pts_info(st, 64, 1, srate_hz);
+    avpriv_update_cur_dts(s, st, 0);
+    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)
+        return ret;
+
+    AV_WL16(st->codecpar->extradata + 0, frame_us / 10);
+    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);
+
+    delay = av_rescale(frame_us == 7500 ? 4000 : 2500, srate_hz, 1000*1000);
+    lc3->end_dts = length ? length + delay : -1;
+
+    return 0;
+}
+
+static int lc3_read_packet(AVFormatContext *s, AVPacket *pkt)
+{
+    LC3DemuxContext *lc3 = s->priv_data;
+    AVStream *st = s->streams[0];
+    AVIOContext *pb = s->pb;
+    int64_t pos = avio_tell(pb);
+    int64_t remaining_samples;
+    int ret;
+
+    ret = av_get_packet(s->pb, pkt, avio_rl16(pb));
+    if (ret < 0)
+        return ret;
+
+    pkt->pos = pos;
+
+    remaining_samples = lc3->end_dts < 0 ? lc3->frame_samples :
+                        FFMAX(lc3->end_dts - ffstream(st)->cur_dts, 0);
+    pkt->duration = FFMIN(lc3->frame_samples, remaining_samples);
+
+    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_GENERIC_INDEX,
+    .priv_data_size = sizeof(LC3DemuxContext),
+    .read_probe     = lc3_read_probe,
+    .read_header    = lc3_read_header,
+    .read_packet    = lc3_read_packet,
+};
+
+#endif /* CONFIG_LC3_DEMUXER */
+
+#if CONFIG_LC3_MUXER
+
+static av_cold int lc3_muxer_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;
+    int frame_us, ep_mode, hr_mode;
+    uint32_t nb_samples = av_rescale_q(
+        st->duration, st->time_base, (AVRational){ 1, srate_hz });
+
+    if (st->codecpar->extradata_size < 6)
+        return AVERROR_INVALIDDATA;
+
+    frame_us = AV_RL16(st->codecpar->extradata + 0) * 10;
+    ep_mode = AV_RL16(st->codecpar->extradata + 2) != 0;
+    hr_mode = AV_RL16(st->codecpar->extradata + 4) != 0;
+
+    if (check_frame_length(s, srate_hz, frame_us) < 0)
+        return AVERROR_INVALIDDATA;
+
+    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_muxer_init,
+    .write_header  = lc3_write_header,
+    .write_packet  = lc3_write_packet,
+};
+
+#endif /* CONFIG_LC3_MUXER */