Re: [FFmpeg-devel] [PATCH 2/5] avcodec/liblc3: Add encoding/decoding support of LC3 audio codec

[Antoine Soulier via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

1. Thanks, I will add the caps.
2. Yes, the `lc3_hr_setup_decoder()` returns the given memory address (And
do not write anything when 'NULL').
But bad parameters also return `NULL`, even if parameters are already
validated elsewhere, I will change this call to be more clean.
> "What makes you believe that this is the only error that can happen?"
The "lc3_hr_encoder_size()" validates the other parameters.
3. Yes, I will.

For the change of the codec ID, I did not know how to implement it.
There are 2 codecs covered:
- LC3, standardized by the Bluetooth SIG, free to use over Bluetooth, and
should only be used over Bluetooth.
- LC3plus, a sibling of LC3, defined by another standard, (ETSI TS 103
634), that can be used anywhere. The chosen parameters conform to one or
other.
Should I declare a second FFCodec and add an option "lc3plus" ?

Thanks.

On Tue, Mar 26, 2024 at 11:28 AM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> 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>
> > Signed-off-by: Antoine SOULIER <asoulier@google.com>
> > ---
> >  libavcodec/Makefile     |   3 +
> >  libavcodec/allcodecs.c  |   3 +
> >  libavcodec/codec_desc.c |  14 +++
> >  libavcodec/codec_id.h   |   2 +
> >  libavcodec/liblc3dec.c  | 146 ++++++++++++++++++++++++++++++
> >  libavcodec/liblc3enc.c  | 191 ++++++++++++++++++++++++++++++++++++++++
> >  6 files changed, 359 insertions(+)
> >  create mode 100644 libavcodec/liblc3dec.c
> >  create mode 100644 libavcodec/liblc3enc.c
> >
> > diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> > index 708434ac76..7d2cf3076d 100644
> > --- a/libavcodec/Makefile
> > +++ b/libavcodec/Makefile
> > @@ -1123,6 +1123,9 @@ 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_LC3_DECODER)         += liblc3dec.o
> > +OBJS-$(CONFIG_LIBLC3_LC3PLUS_DECODER)     += liblc3dec.o
> >  OBJS-$(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..29aedaeac6 100644
> > --- a/libavcodec/allcodecs.c
> > +++ b/libavcodec/allcodecs.c
> > @@ -776,6 +776,9 @@ 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_lc3_decoder;
> > +extern const FFCodec ff_liblc3_lc3plus_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..230bba2a09 100644
> > --- a/libavcodec/codec_desc.c
> > +++ b/libavcodec/codec_desc.c
> > @@ -3425,6 +3425,20 @@ 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,
> > +    },
> > +    {
> > +        .id        = AV_CODEC_ID_LC3_PLUS,
> > +        .type      = AVMEDIA_TYPE_AUDIO,
> > +        .name      = "lc3_plus",
> > +        .long_name = NULL_IF_CONFIG_SMALL("LC3plus (Low Complexity
> Communication Codec plus)"),
> > +        .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..7e4cb39049 100644
> > --- a/libavcodec/codec_id.h
> > +++ b/libavcodec/codec_id.h
> > @@ -543,6 +543,8 @@ enum AVCodecID {
> >      AV_CODEC_ID_AC4,
> >      AV_CODEC_ID_OSQ,
> >      AV_CODEC_ID_QOA,
> > +    AV_CODEC_ID_LC3,
> > +    AV_CODEC_ID_LC3_PLUS,
> >
> >      /* 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..e97cecc68f
> > --- /dev/null
> > +++ b/libavcodec/liblc3dec.c
> > @@ -0,0 +1,146 @@
> > +/*
> > + * 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;
> > +    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 / 1e3f);
> > +    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;
> > +
> > +    for (int ch = 0; ch < channels; ch++) {
> > +        liblc3->decoder[ch] = lc3_hr_setup_decoder(liblc3->hr_mode,
> > +            liblc3->frame_us, liblc3->srate_hz, 0,
> av_malloc(decoder_size));
>
> 1. Leak on error (if this fails for the second channel, then the first
> channel's buffer will not be freed). Use FF_CODEC_CAP_INIT_CLEANUP for
> that.
> 2. Shouldn't there be a check for that av_malloc or is the idea that
> lc3_hr_setup_decoder() checks for us?
> 3. You can allocate the decoders jointly: ptr =
> av_malloc_array(decoder_size, channels) and then use (char*)ptr + ch *
> decoder_size as context for the decoder for channel ch.
> liblc3->decoder[0] would be the actually allocated pointer for freeing.
>
> > +        if (!liblc3->decoder[ch])
> > +            return AVERROR(ENOMEM);
>
> What makes you believe that this is the only error that can happen?
>
> > +    }
> > +
> > +    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;
> > +    int channels = avctx->ch_layout.nb_channels;
> > +
> > +    for (int ch = 0; ch < channels; ch++)
> > +        av_free(liblc3->decoder[ch]);
> > +
> > +    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_lc3_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),
> > +    .init           = liblc3_decode_init,
> > +    .close          = liblc3_decode_close,
> > +    FF_CODEC_DECODE_CB(liblc3_decode),
> > +};
> > +
> > +const FFCodec ff_liblc3_lc3plus_decoder = {
> > +    .p.name         = "liblc3",
> > +    CODEC_LONG_NAME("LC3plus (Low Complexity Communication Codec
> plus)"),
> > +    .p.type         = AVMEDIA_TYPE_AUDIO,
> > +    .p.id           = AV_CODEC_ID_LC3_PLUS,
> > +    .p.capabilities = AV_CODEC_CAP_DR1,
> > +    .p.wrapper_name = "liblc3",
> > +    .priv_data_size = sizeof(LibLC3DecContext),
> > +    .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..6495742c04
> > --- /dev/null
> > +++ b/libavcodec/liblc3enc.c
> > @@ -0,0 +1,191 @@
> > +/*
> > + * 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;
> > +} LibLC3EncOpts;
> > +
> > +typedef struct LibLC3EncContext {
> > +    AVClass *av_class;
> > +    LibLC3EncOpts opts;
> > +    int block_bytes;
> > +    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 <= 5000 || hr_mode)
> > +        avctx->codec_id = AV_CODEC_ID_LC3_PLUS;
>
> The encoder has to encode the format it advertises (via AVCodec.id); it
> must not change it.
> (What is actually the point of this using two different codec ids? You
> do not even need to tell the libraries whether you are decoding/encoding
> the +-version or not.)
>
> > +
> > +    if (frame_us == 7500 && hr_mode) {
> > +        av_log(avctx, AV_LOG_ERROR,
> > +            "High-reolution 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(frame_us, frame_us, srate_hz);
> > +    if (!encoder_size)
> > +        return AVERROR(EINVAL);
> > +
> > +    for (int ch = 0; ch < channels; ch++) {
> > +        liblc3->encoder[ch] = lc3_hr_setup_encoder(
> > +            hr_mode, frame_us, srate_hz, 0, av_malloc(encoder_size));
> > +        if (!liblc3->encoder[ch])
> > +            return AVERROR(ENOMEM);
> > +    }
> > +
> > +    avctx->extradata = av_mallocz(6);
>
> Padding
>
> > +    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);
> > +
> > +    return 0;
> > +}
> > +
> > +static av_cold int liblc3_encode_close(AVCodecContext *avctx)
> > +{
> > +    LibLC3EncContext *liblc3 = avctx->priv_data;
> > +    int channels = avctx->ch_layout.nb_channels;
> > +
> > +    for (int ch = 0; ch < channels; ch++)
> > +        av_free(liblc3->encoder[ch]);
> > +
> > +    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)
> > +        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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