Re: [FFmpeg-devel] [PATCH 2/5] 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>
> ---
>  libavcodec/Makefile     |   2 +
>  libavcodec/allcodecs.c  |   2 +
>  libavcodec/codec_desc.c |   7 ++
>  libavcodec/codec_id.h   |   1 +
>  libavcodec/liblc3dec.c  | 138 +++++++++++++++++++++++++++++
>  libavcodec/liblc3enc.c  | 192 ++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 342 insertions(+)
>  create mode 100644 libavcodec/liblc3dec.c
>  create mode 100644 libavcodec/liblc3enc.c
> 
> 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..bed014652e
> --- /dev/null
> +++ b/libavcodec/liblc3dec.c
> @@ -0,0 +1,138 @@
> +/*
> + * 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;
> +    unsigned decoder_size;
> +
> +    if (avctx->extradata_size < 2)
> +        return AVERROR_INVALIDDATA;
> +
> +    liblc3->frame_us = AV_RL16(avctx->extradata + 0);
> +    liblc3->srate_hz = avctx->sample_rate;
> +    liblc3->hr_mode  = avctx->extradata_size >= 6 &&
> +                       AV_RL16(avctx->extradata + 4);
> +
> +    av_log(avctx, AV_LOG_INFO,
> +        "Decoding %.1f ms frames\n", liblc3->frame_us * 1e-3f);
> +    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);
> +        if (!liblc3->decoder[ch])
> +            return AVERROR_INVALIDDATA;
> +    }
> +
> +    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_free(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 = lc3_hr_frame_samples(
> +        liblc3->hr_mode, liblc3->frame_us, liblc3->srate_hz);
> +    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..f9c72293e3
> --- /dev/null
> +++ b/libavcodec/liblc3enc.c
> @@ -0,0 +1,192 @@
> +/*
> + * 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;
> +    bool hr_mode;

The target of a AV_OPT_TYPE_BOOL option must be of type int.

> +} LibLC3EncOpts;
> +
> +typedef struct LibLC3EncContext {
> +    AVClass *av_class;

const AVClass *

> +    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 / 1e3f);
> +        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 not supported with 7.5 ms frames\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    av_log(avctx, AV_LOG_INFO, "Encoding %.1f ms frames\n", frame_us / 1e3f);
> +    if (hr_mode)
> +        av_log(avctx, AV_LOG_INFO, "High-resolution mode 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);
> +        if (!liblc3->encoder[ch])
> +            return AVERROR(EINVAL);
> +    }
> +
> +    avctx->extradata = av_mallocz(6 + AV_INPUT_BUFFER_PADDING_SIZE);
> +    if (!avctx->extradata)
> +        return AVERROR(ENOMEM);
> +
> +    AV_WL16(avctx->extradata + 0, frame_us);
> +    AV_WL16(avctx->extradata + 2, 0);
> +    AV_WL16(avctx->extradata + 4, hr_mode);
> +    avctx->extradata_size = 6;
> +
> +    avctx->frame_size = lc3_hr_frame_samples(hr_mode, frame_us, srate_hz);

Does this function do anything else than frame_us * srate_hz / 1000?

> +
> +    return 0;
> +}
> +
> +static av_cold int liblc3_encode_close(AVCodecContext *avctx)
> +{
> +    LibLC3EncContext *liblc3 = avctx->priv_data;
> +
> +    av_free(liblc3->encoder_mem);

av_freep is preferred so as not to leave dangling pointers behind.

> +
> +    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_alloc_packet(avctx, avpkt, block_bytes)) < 0)

It seems that lc3 has a fixed blocksize. If so, you should use
ff_get_encode_buffer().

> +        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),
> +};

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