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

[Stefano Sabatini]

On date Tuesday 2024-03-26 23:07:54 +0000, ffmpeg-devel Mailing List wrote:
> 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 at 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
[...] 
> +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);

readability: use 1000f since it's more explicit

> +    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);

do you need to reset/free the encoder in case of failure? If this is
the case you need to unset/free here or in the close function

[...]

> +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);

can this fail?

[...]