Re: [FFmpeg-devel] [PATCH 1/2] avcodec/liblc3: Add encoding/decoding support of LC3 audio codec

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

Antoine Soulier via ffmpeg-devel:
> The LC3 audio codec is the default codec of Bluetooth LE audio.
> This is a wrapper over the liblc3 library (https://github.com/google/liblc3).
> 
> Signed-off-by: Antoine Soulier <asoulier@google.com>
> ---
>  Changelog                 |   4 +
>  configure                 |   6 ++
>  doc/encoders.texi         |  57 ++++++++++++
>  doc/general_contents.texi |  11 ++-
>  libavcodec/Makefile       |   2 +
>  libavcodec/allcodecs.c    |   2 +
>  libavcodec/codec_desc.c   |   7 ++
>  libavcodec/codec_id.h     |   1 +
>  libavcodec/liblc3dec.c    | 141 ++++++++++++++++++++++++++++
>  libavcodec/liblc3enc.c    | 190 ++++++++++++++++++++++++++++++++++++++
>  10 files changed, 420 insertions(+), 1 deletion(-)
>  create mode 100644 libavcodec/liblc3dec.c
>  create mode 100644 libavcodec/liblc3enc.c
> 
> diff --git a/Changelog b/Changelog
> index e83a00e35c..83a4cf7888 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -1,6 +1,10 @@
>  Entries are sorted chronologically from oldest to youngest within each release,
>  releases are sorted from youngest to oldest.
>  
> +version <next>:
> +- LC3/LC3plus decoding/encoding using external library liblc3
> +
> +
>  version 7.0:
>  - DXV DXT1 encoder
>  - LEAD MCMP decoder
> diff --git a/configure b/configure
> index 2d46ef0b9c..e5d9ba9f53 100755
> --- a/configure
> +++ b/configure
> @@ -244,6 +244,7 @@ External library support:
>    --enable-libjxl          enable JPEG XL de/encoding via libjxl [no]
>    --enable-libklvanc       enable Kernel Labs VANC processing [no]
>    --enable-libkvazaar      enable HEVC encoding via libkvazaar [no]
> +  --enable-liblc3          enable LC3 de/encoding via liblc3 [no]
>    --enable-liblensfun      enable lensfun lens correction [no]
>    --enable-libmodplug      enable ModPlug via libmodplug [no]
>    --enable-libmp3lame      enable MP3 encoding via libmp3lame [no]
> @@ -1926,6 +1927,7 @@ EXTERNAL_LIBRARY_LIST="
>      libjxl
>      libklvanc
>      libkvazaar
> +    liblc3
>      libmodplug
>      libmp3lame
>      libmysofa
> @@ -3499,6 +3501,9 @@ libilbc_encoder_deps="libilbc"
>  libjxl_decoder_deps="libjxl libjxl_threads"
>  libjxl_encoder_deps="libjxl libjxl_threads"
>  libkvazaar_encoder_deps="libkvazaar"
> +liblc3_decoder_deps="liblc3"
> +liblc3_encoder_deps="liblc3"
> +liblc3_encoder_select="audio_frame_queue"
>  libmodplug_demuxer_deps="libmodplug"
>  libmp3lame_encoder_deps="libmp3lame"
>  libmp3lame_encoder_select="audio_frame_queue mpegaudioheader"
> @@ -6869,6 +6874,7 @@ enabled libjxl            && require_pkg_config libjxl "libjxl >= 0.7.0" jxl/dec
>                               require_pkg_config libjxl_threads "libjxl_threads >= 0.7.0" jxl/thread_parallel_runner.h JxlThreadParallelRunner
>  enabled libklvanc         && require libklvanc libklvanc/vanc.h klvanc_context_create -lklvanc
>  enabled libkvazaar        && require_pkg_config libkvazaar "kvazaar >= 2.0.0" kvazaar.h kvz_api_get
> +enabled liblc3            && require_pkg_config liblc3 "lc3 >= 1.1.0" lc3.h lc3_hr_setup_encoder
>  enabled liblensfun        && require_pkg_config liblensfun lensfun lensfun.h lf_db_create
>  
>  if enabled libmfx && enabled libvpl; then
> diff --git a/doc/encoders.texi b/doc/encoders.texi
> index 7c223ed74c..66847191e1 100644
> --- a/doc/encoders.texi
> +++ b/doc/encoders.texi
> @@ -814,6 +814,63 @@ ffmpeg -i input.wav -c:a libfdk_aac -profile:a aac_he -b:a 64k output.m4a
>  @end example
>  @end itemize
>  
> +@anchor{liblc3-enc}
> +@section liblc3
> +
> +liblc3 LC3 (Low Complexity Communication Codec) encoder wrapper.
> +
> +Requires the presence of the liblc3 headers and library during configuration.
> +You need to explicitly configure the build with @code{--enable-liblc3}.
> +
> +This encoder has support for the Bluetooth SIG LC3 codec for the LE Audio
> +protocol, and the following features of LC3plus:
> +@itemize
> +@item
> +Frame duration of 2.5 and 5ms.
> +@item
> +High-Resolution mode, 48 KHz, and 96 kHz sampling rates.
> +@end itemize
> +
> +For more information see the liblc3 project at
> +@url{https://github.com/google/liblc3}.
> +
> +@subsection Options
> +
> +The following options are mapped on the shared FFmpeg codec options.
> +
> +@table @option
> +@item b @var{bitrate}
> +Set the bit rate in bits/s. This will determine the fixed size of the encoded
> +frames, for a selected frame duration.
> +
> +@item ar @var{frequency}
> +Set the audio sampling rate (in Hz).
> +
> +@item channels
> +Set the number of audio channels.
> +
> +@item frame_duration
> +Set the audio frame duration in milliseconds. Default value is 10ms.
> +Allowed frame durations are 2.5ms, 5ms, 7.5ms and 10ms.
> +LC3 (Bluetooth LE Audio), allows 7.5ms and 10ms; and LC3plus 2.5ms, 5ms
> +and 10ms.
> +
> +The 10ms frame duration is available in LC3 and LC3 plus standard.
> +In this mode, the produced bitstream can be referenced either as LC3 or LC3plus.
> +
> +@item high_resolution @var{boolean}
> +Enable the high-resolution mode if set to 1. The high-resolution mode is
> +available with all LC3plus frame durations and for a sampling rate of 48 KHz,
> +and 96 KHz.
> +
> +The encoder automatically turns off this mode at lower sampling rates and
> +activates it at 96 KHz.
> +
> +This mode should be preferred at high bitrates. In this mode, the audio
> +bandwidth is always up to the Nyquist frequency, compared to LC3 at 48 KHz,
> +which limits the bandwidth to 20 KHz.
> +@end table
> +
>  @anchor{libmp3lame}
>  @section libmp3lame
>  
> diff --git a/doc/general_contents.texi b/doc/general_contents.texi
> index f269cbd1a9..e7cf4f8239 100644
> --- a/doc/general_contents.texi
> +++ b/doc/general_contents.texi
> @@ -237,6 +237,14 @@ Go to @url{http://sourceforge.net/projects/opencore-amr/} and follow the
>  instructions for installing the library.
>  Then pass @code{--enable-libfdk-aac} to configure to enable it.
>  
> +@subsection LC3 library
> +
> +FFmpeg can make use of the Google LC3 library for LC3 decoding & encoding.
> +
> +Go to @url{https://github.com/google/liblc3/} and follow the instructions for
> +installing the library.
> +Then pass @code{--enable-liblc3} to configure to enable it.
> +
>  @section OpenH264
>  
>  FFmpeg can make use of the OpenH264 library for H.264 decoding and encoding.
> @@ -1300,7 +1308,8 @@ following image formats are supported:
>      @tab encoding and decoding supported through external library libilbc
>  @item IMC (Intel Music Coder)  @tab     @tab  X
>  @item Interplay ACM            @tab     @tab  X
> -@item MACE (Macintosh Audio Compression/Expansion) 3:1  @tab     @tab  X
> +@item LC3                    @tab E  @tab  E
> +    @tab supported through external library liblc3
>  @item MACE (Macintosh Audio Compression/Expansion) 6:1  @tab     @tab  X
>  @item Marian's A-pac audio     @tab     @tab  X
>  @item MI-SC4 (Micronas SC-4 Audio)  @tab     @tab  X
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index 9ce6d445c1..e70811dbd6 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -1123,6 +1123,8 @@ OBJS-$(CONFIG_LIBILBC_ENCODER)            += libilbc.o
>  OBJS-$(CONFIG_LIBJXL_DECODER)             += libjxldec.o libjxl.o
>  OBJS-$(CONFIG_LIBJXL_ENCODER)             += libjxlenc.o libjxl.o
>  OBJS-$(CONFIG_LIBKVAZAAR_ENCODER)         += libkvazaar.o
> +OBJS-$(CONFIG_LIBLC3_ENCODER)             += liblc3enc.o
> +OBJS-$(CONFIG_LIBLC3_DECODER)             += liblc3dec.o
>  OBJS-$(CONFIG_LIBMP3LAME_ENCODER)         += libmp3lame.o
>  OBJS-$(CONFIG_LIBOPENCORE_AMRNB_DECODER)  += libopencore-amr.o
>  OBJS-$(CONFIG_LIBOPENCORE_AMRNB_ENCODER)  += libopencore-amr.o
> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> index 2386b450a6..f4705651fb 100644
> --- a/libavcodec/allcodecs.c
> +++ b/libavcodec/allcodecs.c
> @@ -776,6 +776,8 @@ extern const FFCodec ff_libilbc_encoder;
>  extern const FFCodec ff_libilbc_decoder;
>  extern const FFCodec ff_libjxl_decoder;
>  extern const FFCodec ff_libjxl_encoder;
> +extern const FFCodec ff_liblc3_encoder;
> +extern const FFCodec ff_liblc3_decoder;
>  extern const FFCodec ff_libmp3lame_encoder;
>  extern const FFCodec ff_libopencore_amrnb_encoder;
>  extern const FFCodec ff_libopencore_amrnb_decoder;
> diff --git a/libavcodec/codec_desc.c b/libavcodec/codec_desc.c
> index 3bab86db62..7dba61dc8b 100644
> --- a/libavcodec/codec_desc.c
> +++ b/libavcodec/codec_desc.c
> @@ -3425,6 +3425,13 @@ static const AVCodecDescriptor codec_descriptors[] = {
>          .long_name = NULL_IF_CONFIG_SMALL("QOA (Quite OK Audio)"),
>          .props     = AV_CODEC_PROP_INTRA_ONLY | AV_CODEC_PROP_LOSSY,
>      },
> +    {
> +        .id        = AV_CODEC_ID_LC3,
> +        .type      = AVMEDIA_TYPE_AUDIO,
> +        .name      = "lc3",
> +        .long_name = NULL_IF_CONFIG_SMALL("LC3 (Low Complexity Communication Codec)"),
> +        .props     = AV_CODEC_PROP_INTRA_ONLY | AV_CODEC_PROP_LOSSY,
> +    },
>  
>      /* subtitle codecs */
>      {
> diff --git a/libavcodec/codec_id.h b/libavcodec/codec_id.h
> index c8dc21da74..0ab1e34a61 100644
> --- a/libavcodec/codec_id.h
> +++ b/libavcodec/codec_id.h
> @@ -543,6 +543,7 @@ enum AVCodecID {
>      AV_CODEC_ID_AC4,
>      AV_CODEC_ID_OSQ,
>      AV_CODEC_ID_QOA,
> +    AV_CODEC_ID_LC3,
>  
>      /* subtitle codecs */
>      AV_CODEC_ID_FIRST_SUBTITLE = 0x17000,          ///< A dummy ID pointing at the start of subtitle codecs.
> diff --git a/libavcodec/liblc3dec.c b/libavcodec/liblc3dec.c
> new file mode 100644
> index 0000000000..32d8fade91
> --- /dev/null
> +++ b/libavcodec/liblc3dec.c
> @@ -0,0 +1,141 @@
> +/*
> + * LC3 decoder wrapper
> + * Copyright (C) 2024  Antoine Soulier <asoulier@google.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * Permission to use, copy, modify, and/or distribute this software for any
> + * purpose with or without fee is hereby granted, provided that the above
> + * copyright notice and this permission notice appear in all copies.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
> + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
> + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
> + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
> + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
> + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
> + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
> + */
> +
> +#include <lc3.h>
> +
> +#include "libavutil/intreadwrite.h"
> +
> +#include "avcodec.h"
> +#include "codec.h"
> +#include "codec_internal.h"
> +#include "decode.h"
> +#include "internal.h"
> +
> +#define DECODER_MAX_CHANNELS  2
> +
> +typedef struct LibLC3DecContext {
> +    int frame_us, srate_hz;
> +    bool hr_mode;
> +    void *decoder_mem;
> +    lc3_decoder_t decoder[DECODER_MAX_CHANNELS];
> +} LibLC3DecContext;
> +
> +static av_cold int liblc3_decode_init(AVCodecContext *avctx)
> +{
> +    LibLC3DecContext *liblc3 = avctx->priv_data;
> +    int channels = avctx->ch_layout.nb_channels;
> +    int ep_mode;
> +    unsigned decoder_size;
> +
> +    if (avctx->extradata_size < 6)
> +        return AVERROR_INVALIDDATA;
> +
> +    liblc3->frame_us = AV_RL16(avctx->extradata + 0) * 10;
> +    liblc3->srate_hz = avctx->sample_rate;
> +    ep_mode          = AV_RL16(avctx->extradata + 2);
> +    liblc3->hr_mode  = AV_RL16(avctx->extradata + 4);
> +    if (ep_mode != 0) {
> +        av_log(avctx, AV_LOG_ERROR,
> +               "Error protection mode is not supported.\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    av_log(avctx, AV_LOG_INFO,
> +           "Decoding %.1f ms frames.\n", liblc3->frame_us / 1000.f);
> +    if (liblc3->hr_mode)
> +        av_log(avctx, AV_LOG_INFO, "High-resolution mode enabled.\n");
> +
> +    decoder_size = lc3_hr_decoder_size(
> +        liblc3->hr_mode, liblc3->frame_us, liblc3->srate_hz);
> +    if (!decoder_size)
> +        return AVERROR_INVALIDDATA;
> +
> +    liblc3->decoder_mem = av_malloc_array(channels, decoder_size);
> +    if (!liblc3->decoder_mem)
> +        return AVERROR(ENOMEM);
> +
> +    for (int ch = 0; ch < channels; ch++) {
> +        liblc3->decoder[ch] = lc3_hr_setup_decoder(
> +            liblc3->hr_mode, liblc3->frame_us, liblc3->srate_hz, 0,
> +            (char *)liblc3->decoder_mem + ch * decoder_size);
> +    }
> +
> +    avctx->sample_fmt = AV_SAMPLE_FMT_FLTP;
> +    avctx->delay = lc3_hr_delay_samples(
> +        liblc3->hr_mode, liblc3->frame_us, liblc3->srate_hz);
> +    avctx->internal->skip_samples = avctx->delay;
> +
> +    return 0;
> +}
> +
> +static av_cold int liblc3_decode_close(AVCodecContext *avctx)
> +{
> +    LibLC3DecContext *liblc3 = avctx->priv_data;
> +
> +    av_freep(&liblc3->decoder_mem);
> +
> +    return 0;
> +}
> +
> +static int liblc3_decode(AVCodecContext *avctx, AVFrame *frame,
> +                         int *got_frame_ptr, AVPacket *avpkt)
> +{
> +    LibLC3DecContext *liblc3 = avctx->priv_data;
> +    int channels = avctx->ch_layout.nb_channels;
> +    uint8_t *in = avpkt->data;
> +    int block_bytes, ret;
> +
> +    frame->nb_samples = av_rescale(
> +        liblc3->frame_us, liblc3->srate_hz, 1000*1000);
> +    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
> +        return ret;
> +
> +    block_bytes = avpkt->size;
> +    for (int ch = 0; ch < channels; ch++) {
> +        int frame_bytes = block_bytes / channels
> +            + (ch < block_bytes % channels);
> +
> +        ret = lc3_decode(liblc3->decoder[ch], in, frame_bytes,
> +                         LC3_PCM_FORMAT_FLOAT, frame->data[ch], 1);
> +        if (ret < 0)
> +            return AVERROR_INVALIDDATA;
> +
> +        in += frame_bytes;
> +    }
> +
> +    frame->nb_samples = FFMIN(frame->nb_samples, avpkt->duration);
> +
> +    *got_frame_ptr = 1;
> +
> +    return avpkt->size;
> +}
> +
> +const FFCodec ff_liblc3_decoder = {
> +    .p.name         = "liblc3",
> +    CODEC_LONG_NAME("LC3 (Low Complexity Communication Codec)"),
> +    .p.type         = AVMEDIA_TYPE_AUDIO,
> +    .p.id           = AV_CODEC_ID_LC3,
> +    .p.capabilities = AV_CODEC_CAP_DR1,
> +    .p.wrapper_name = "liblc3",
> +    .priv_data_size = sizeof(LibLC3DecContext),
> +    .caps_internal  = FF_CODEC_CAP_INIT_CLEANUP,
> +    .init           = liblc3_decode_init,
> +    .close          = liblc3_decode_close,
> +    FF_CODEC_DECODE_CB(liblc3_decode),
> +};
> diff --git a/libavcodec/liblc3enc.c b/libavcodec/liblc3enc.c
> new file mode 100644
> index 0000000000..7d5d92303c
> --- /dev/null
> +++ b/libavcodec/liblc3enc.c
> @@ -0,0 +1,190 @@
> +/*
> + * LC3 encoder wrapper
> + * Copyright (C) 2024  Antoine Soulier <asoulier@google.com>
> + *
> + * This file is part of FFmpeg.
> + *
> + * Permission to use, copy, modify, and/or distribute this software for any
> + * purpose with or without fee is hereby granted, provided that the above
> + * copyright notice and this permission notice appear in all copies.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
> + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
> + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
> + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
> + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
> + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
> + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
> + */
> +
> +#include <lc3.h>
> +
> +#include "libavutil/intreadwrite.h"
> +#include "libavutil/opt.h"
> +
> +#include "avcodec.h"
> +#include "codec.h"
> +#include "codec_internal.h"
> +#include "encode.h"
> +
> +#define ENCODER_MAX_CHANNELS  2
> +
> +typedef struct LibLC3EncOpts {
> +    float frame_duration;
> +    int hr_mode;
> +} LibLC3EncOpts;
> +
> +typedef struct LibLC3EncContext {
> +    const AVClass *av_class;
> +    LibLC3EncOpts opts;
> +    int block_bytes;
> +    void *encoder_mem;
> +    lc3_encoder_t encoder[ENCODER_MAX_CHANNELS];
> +} LibLC3EncContext;
> +
> +static av_cold int liblc3_encode_init(AVCodecContext *avctx)
> +{
> +    LibLC3EncContext *liblc3 = avctx->priv_data;
> +    bool hr_mode = liblc3->opts.hr_mode;
> +    int frame_us = liblc3->opts.frame_duration * 1000;
> +    int srate_hz = avctx->sample_rate;
> +    int channels = avctx->ch_layout.nb_channels;
> +    int effective_bit_rate;
> +    unsigned encoder_size;
> +
> +    if (frame_us != 2500 && frame_us !=  5000 &&
> +        frame_us != 7500 && frame_us != 10000   ) {
> +        av_log(avctx, AV_LOG_ERROR,
> +               "Unsupported frame duration %.1f ms.\n", frame_us / 1000.f);
> +        return AVERROR(EINVAL);
> +    }
> +
> +    hr_mode |= srate_hz > 48000;
> +    hr_mode &= srate_hz >= 48000;
> +
> +    if (frame_us == 7500 && hr_mode) {
> +        av_log(avctx, AV_LOG_ERROR,
> +               "High-resolution mode is not supported with 7.5 ms frames.\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    av_log(avctx, AV_LOG_INFO, "Encoding %.1f ms frames.\n", frame_us / 1000.f);
> +    if (hr_mode)
> +        av_log(avctx, AV_LOG_INFO, "High-resolution mode is enabled.\n");
> +
> +    liblc3->block_bytes = lc3_hr_frame_block_bytes(
> +        hr_mode, frame_us, srate_hz, channels, avctx->bit_rate);
> +
> +    effective_bit_rate = lc3_hr_resolve_bitrate(
> +        hr_mode, frame_us, srate_hz, liblc3->block_bytes);
> +
> +    if (avctx->bit_rate != effective_bit_rate)
> +        av_log(avctx, AV_LOG_WARNING,
> +               "Bitrate changed to %d bps.\n", effective_bit_rate);
> +    avctx->bit_rate = effective_bit_rate;
> +
> +    encoder_size = lc3_hr_encoder_size(hr_mode, frame_us, srate_hz);
> +    if (!encoder_size)
> +        return AVERROR(EINVAL);
> +
> +    liblc3->encoder_mem = av_malloc_array(channels, encoder_size);
> +    if (!liblc3->encoder_mem)
> +        return AVERROR(ENOMEM);
> +
> +    for (int ch = 0; ch < channels; ch++) {
> +        liblc3->encoder[ch] = lc3_hr_setup_encoder(
> +            hr_mode, frame_us, srate_hz, 0,
> +            (char *)liblc3->encoder_mem + ch * encoder_size);
> +    }
> +
> +    avctx->extradata = av_mallocz(6 + AV_INPUT_BUFFER_PADDING_SIZE);
> +    if (!avctx->extradata)
> +        return AVERROR(ENOMEM);
> +
> +    AV_WL16(avctx->extradata + 0, frame_us / 10);
> +    AV_WL16(avctx->extradata + 2, 0);
> +    AV_WL16(avctx->extradata + 4, hr_mode);
> +    avctx->extradata_size = 6;
> +
> +    avctx->frame_size = av_rescale(frame_us, srate_hz, 1000*1000);
> +
> +    return 0;
> +}
> +
> +static av_cold int liblc3_encode_close(AVCodecContext *avctx)
> +{
> +    LibLC3EncContext *liblc3 = avctx->priv_data;
> +
> +    av_freep(&liblc3->encoder_mem);
> +
> +    return 0;
> +}
> +
> +static int liblc3_encode(AVCodecContext *avctx, AVPacket *avpkt,
> +                         const AVFrame *av_frame, int *got_packet_ptr)
> +{
> +    LibLC3EncContext *liblc3 = avctx->priv_data;
> +    int block_bytes = liblc3->block_bytes;
> +    int channels = avctx->ch_layout.nb_channels;
> +    uint8_t *data_ptr;
> +    int ret;
> +
> +    if ((ret = ff_get_encode_buffer(avctx, avpkt, block_bytes, 0)) < 0)
> +        return ret;
> +
> +    data_ptr = avpkt->data;
> +    for (int ch = 0; ch < channels; ch++) {
> +        int frame_bytes = block_bytes / channels
> +                + (ch < block_bytes % channels);
> +
> +        lc3_encode(liblc3->encoder[ch],
> +                   LC3_PCM_FORMAT_FLOAT, av_frame->data[ch], 1,
> +                   frame_bytes, data_ptr);
> +
> +        data_ptr += frame_bytes;
> +    }
> +
> +    *got_packet_ptr = 1;
> +
> +    return 0;
> +}
> +
> +#define OFFSET(x) offsetof(LibLC3EncContext, opts.x)
> +#define FLAGS AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
> +static const AVOption options[] = {
> +    { "frame_duration", "Duration of a frame in milliseconds",
> +        OFFSET(frame_duration), AV_OPT_TYPE_FLOAT,
> +        { .dbl = 10.0 }, 2.5, 10.0, FLAGS },
> +    { "high_resolution", "Enable High-Resolution mode (48 KHz or 96 KHz)",
> +        OFFSET(hr_mode), AV_OPT_TYPE_BOOL,
> +        { .i64 = 0 }, 0, 1, FLAGS },
> +    { NULL }
> +};
> +
> +static const AVClass class = {
> +    .class_name = "liblc3 encoder",
> +    .item_name  = av_default_item_name,
> +    .option     = options,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
> +const FFCodec ff_liblc3_encoder = {
> +    .p.name         = "liblc3",
> +    CODEC_LONG_NAME("LC3 (Low Complexity Communication Codec)"),
> +    .p.type         = AVMEDIA_TYPE_AUDIO,
> +    .p.id           = AV_CODEC_ID_LC3,
> +    .p.capabilities = AV_CODEC_CAP_DR1,
> +    .p.ch_layouts = (const AVChannelLayout[])
> +        { { AV_CHANNEL_ORDER_UNSPEC, 1 },
> +          { AV_CHANNEL_ORDER_UNSPEC, 2 }, { 0 } },
> +    .p.supported_samplerates = (const int [])
> +        { 96000, 48000, 32000, 24000, 16000, 8000, 0 },
> +    .p.sample_fmts = (const enum AVSampleFormat[])
> +        { AV_SAMPLE_FMT_FLTP, AV_SAMPLE_FMT_NONE },
> +    .p.priv_class   = &class,
> +    .p.wrapper_name = "liblc3",
> +    .priv_data_size = sizeof(LibLC3EncContext),
> +    .init           = liblc3_encode_init,
> +    .close          = liblc3_encode_close,
> +    FF_CODEC_ENCODE_CB(liblc3_encode),
> +};

How likely is it actually that a future decoder/encoder will only handle
LC3 or only LC3plus? (Yes, I know that I have suggested using only one
codec id, but if it is possible/likely for the answer to the preceding
question to be "yes", then using two codec ids might be better indeed.)

- Andreas

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