[FFmpeg-devel] [PATCH 2/2] libavcodec/ac3_parser: add avpriv function to parse EC3SpecificBox (dec3)

[James Almer]

On 10/2/2020 10:10 AM, Nachiket Tarate wrote:
> This will be used by HLS demuxer for SAMPLE-AES decryption.
> 
> Signed-off-by: Nachiket Tarate <nachiket.tarate at outlook.com>
> ---
>  libavcodec/ac3_parser.c          | 47 ++++++++++++++++++++++++++++++++
>  libavcodec/ac3_parser_internal.h |  4 +++
>  2 files changed, 51 insertions(+)
> 
> diff --git a/libavcodec/ac3_parser.c b/libavcodec/ac3_parser.c
> index ba171653ef..a8fdde0ff9 100644
> --- a/libavcodec/ac3_parser.c
> +++ b/libavcodec/ac3_parser.c
> @@ -2,6 +2,7 @@
>   * AC-3 parser
>   * Copyright (c) 2003 Fabrice Bellard
>   * Copyright (c) 2003 Michael Niedermayer
> + * Copyright (c) 2020 Nachiket Tarate
>   *
>   * This file is part of FFmpeg.
>   *
> @@ -172,6 +173,47 @@ int avpriv_ac3_parse_header(AC3HeaderInfo **phdr, const uint8_t *buf,
>      return get_bits_count(&gb);
>  }
>  
> +/*
> + * Parse 'dec3' EC3SpecificBox
> + */
> +int avpriv_eac3_parse_dec3(AC3HeaderInfo **phdr, const uint8_t *buf, size_t size)
> +{
> +    GetBitContext gb;
> +    AC3HeaderInfo *hdr;
> +    int err;
> +
> +    int data_rate, fscod, acmod, lfeon;
> +
> +    if (!*phdr)
> +        *phdr = av_mallocz(sizeof(AC3HeaderInfo));
> +    if (!*phdr)
> +        return AVERROR(ENOMEM);
> +    hdr = *phdr;
> +
> +    err = init_get_bits8(&gb, buf, size);
> +    if (err < 0)
> +        return AVERROR_INVALIDDATA;
> +
> +    data_rate = get_bits(&gb, 13);
> +    skip_bits(&gb, 3);
> +    fscod = get_bits(&gb, 2);
> +    skip_bits(&gb, 10);
> +    acmod = get_bits(&gb, 3);
> +    lfeon = get_bits(&gb, 1);
> +
> +    hdr->sample_rate = ff_ac3_sample_rate_tab[fscod];

Why not instead just make this array avpriv_? Everything else can be
done within libavformat. See mov_read_dec3() in mov.c

> +
> +    hdr->channels = ff_ac3_channels_tab[acmod] + lfeon;
> +
> +    hdr->channel_layout = avpriv_ac3_channel_layout_tab[acmod];
> +    if (lfeon)
> +        hdr->channel_layout |= AV_CH_LOW_FREQUENCY;
> + 
> +    hdr->bit_rate = data_rate*1000;
> +
> +    return 0;
> +}
> +
>  int av_ac3_parse_header(const uint8_t *buf, size_t size,
>                          uint8_t *bitstream_id, uint16_t *frame_size)
>  {
> @@ -256,6 +298,11 @@ int avpriv_ac3_parse_header(AC3HeaderInfo **phdr, const uint8_t *buf,
>      return AVERROR(ENOSYS);
>  }
>  
> +int avpriv_eac3_parse_dec3(AC3HeaderInfo **phdr, const uint8_t *buf, size_t size)
> +{
> +    return AVERROR(ENOSYS);
> +}
> +
>  int av_ac3_parse_header(const uint8_t *buf, size_t size,
>                          uint8_t *bitstream_id, uint16_t *frame_size)
>  {
> diff --git a/libavcodec/ac3_parser_internal.h b/libavcodec/ac3_parser_internal.h
> index 3648802a73..0388a5bb5e 100644
> --- a/libavcodec/ac3_parser_internal.h
> +++ b/libavcodec/ac3_parser_internal.h
> @@ -38,5 +38,9 @@ int ff_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr);
>  
>  int avpriv_ac3_parse_header(AC3HeaderInfo **hdr, const uint8_t *buf,
>                              size_t size);
> +/*
> + * Parse 'dec3' EC3SpecificBox
> + */
> +int avpriv_eac3_parse_dec3(AC3HeaderInfo **phdr, const uint8_t *buf, size_t size);
>  
>  #endif /* AVCODEC_AC3_PARSER_INTERNAL_H */
>