[FFmpeg-devel] [PATCH 1/4] aac_latm: Allow unaligned AudioSpecificConfig

[James Almer]

On 2/9/2017 2:40 PM, Alex Converse wrote:
> diff --git a/libavcodec/mpeg4audio.c b/libavcodec/mpeg4audio.c
> index 5f85b64cb8..9fe257838c 100644
> --- a/libavcodec/mpeg4audio.c
> +++ b/libavcodec/mpeg4audio.c
> @@ -83,70 +83,62 @@ static inline int get_sample_rate(GetBitContext *gb, int *index)
>          avpriv_mpeg4audio_sample_rates[*index];
>  }
>  
> -int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf,
> -                                 int bit_size, int sync_extension)
> +int avpriv_mpeg4audio_get_config_gb(MPEG4AudioConfig *c, GetBitContext *gb,
> +                                    int sync_extension)

Please, keep this new function internal (ff_ prefix) until it's actually
needed by libavformat.

>  {
> -    GetBitContext gb;
>      int specific_config_bitindex, ret;
> -
> -    if (bit_size <= 0)
> -        return AVERROR_INVALIDDATA;
> -
> -    ret = init_get_bits(&gb, buf, bit_size);
> -    if (ret < 0)
> -        return ret;
> -
> -    c->object_type = get_object_type(&gb);
> -    c->sample_rate = get_sample_rate(&gb, &c->sampling_index);
> -    c->chan_config = get_bits(&gb, 4);
> +    int start_bit_index = get_bits_count(gb);
> +    c->object_type = get_object_type(gb);
> +    c->sample_rate = get_sample_rate(gb, &c->sampling_index);
> +    c->chan_config = get_bits(gb, 4);
>      if (c->chan_config < FF_ARRAY_ELEMS(ff_mpeg4audio_channels))
>          c->channels = ff_mpeg4audio_channels[c->chan_config];
>      c->sbr = -1;
>      c->ps  = -1;
>      if (c->object_type == AOT_SBR || (c->object_type == AOT_PS &&
>          // check for W6132 Annex YYYY draft MP3onMP4
> -        !(show_bits(&gb, 3) & 0x03 && !(show_bits(&gb, 9) & 0x3F)))) {
> +        !(show_bits(gb, 3) & 0x03 && !(show_bits(gb, 9) & 0x3F)))) {
>          if (c->object_type == AOT_PS)
>              c->ps = 1;
>          c->ext_object_type = AOT_SBR;
>          c->sbr = 1;
> -        c->ext_sample_rate = get_sample_rate(&gb, &c->ext_sampling_index);
> -        c->object_type = get_object_type(&gb);
> +        c->ext_sample_rate = get_sample_rate(gb, &c->ext_sampling_index);
> +        c->object_type = get_object_type(gb);
>          if (c->object_type == AOT_ER_BSAC)
> -            c->ext_chan_config = get_bits(&gb, 4);
> +            c->ext_chan_config = get_bits(gb, 4);
>      } else {
>          c->ext_object_type = AOT_NULL;
>          c->ext_sample_rate = 0;
>      }
> -    specific_config_bitindex = get_bits_count(&gb);
> +    specific_config_bitindex = get_bits_count(gb);
>  
>      if (c->object_type == AOT_ALS) {
> -        skip_bits(&gb, 5);
> -        if (show_bits_long(&gb, 24) != MKBETAG('\0','A','L','S'))
> -            skip_bits_long(&gb, 24);
> +        skip_bits(gb, 5);
> +        if (show_bits_long(gb, 24) != MKBETAG('\0','A','L','S'))
> +            skip_bits_long(gb, 24);
>  
> -        specific_config_bitindex = get_bits_count(&gb);
> +        specific_config_bitindex = get_bits_count(gb);
>  
> -        ret = parse_config_ALS(&gb, c);
> +        ret = parse_config_ALS(gb, c);
>          if (ret < 0)
>              return ret;
>      }
>  
>      if (c->ext_object_type != AOT_SBR && sync_extension) {
> -        while (get_bits_left(&gb) > 15) {
> -            if (show_bits(&gb, 11) == 0x2b7) { // sync extension
> -                get_bits(&gb, 11);
> -                c->ext_object_type = get_object_type(&gb);
> -                if (c->ext_object_type == AOT_SBR && (c->sbr = get_bits1(&gb)) == 1) {
> -                    c->ext_sample_rate = get_sample_rate(&gb, &c->ext_sampling_index);
> +        while (get_bits_left(gb) > 15) {
> +            if (show_bits(gb, 11) == 0x2b7) { // sync extension
> +                get_bits(gb, 11);
> +                c->ext_object_type = get_object_type(gb);
> +                if (c->ext_object_type == AOT_SBR && (c->sbr = get_bits1(gb)) == 1) {
> +                    c->ext_sample_rate = get_sample_rate(gb, &c->ext_sampling_index);
>                      if (c->ext_sample_rate == c->sample_rate)
>                          c->sbr = -1;
>                  }
> -                if (get_bits_left(&gb) > 11 && get_bits(&gb, 11) == 0x548)
> -                    c->ps = get_bits1(&gb);
> +                if (get_bits_left(gb) > 11 && get_bits(gb, 11) == 0x548)
> +                    c->ps = get_bits1(gb);
>                  break;
>              } else
> -                get_bits1(&gb); // skip 1 bit
> +                get_bits1(gb); // skip 1 bit
>          }
>      }
>  
> @@ -157,7 +149,23 @@ int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf,
>      if ((c->ps == -1 && c->object_type != AOT_AAC_LC) || c->channels & ~0x01)
>          c->ps = 0;
>  
> -    return specific_config_bitindex;
> +    return specific_config_bitindex - start_bit_index;
> +}
> +
> +int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf,
> +                                 int bit_size, int sync_extension)
> +{
> +    GetBitContext gb;
> +    int ret;
> +
> +    if (bit_size <= 0)
> +        return AVERROR_INVALIDDATA;
> +
> +    ret = init_get_bits(&gb, buf, bit_size);
> +    if (ret < 0)
> +        return ret;
> +
> +    return avpriv_mpeg4audio_get_config_gb(c, &gb, sync_extension);
>  }
>  
>  static av_always_inline unsigned int copy_bits(PutBitContext *pb,
> diff --git a/libavcodec/mpeg4audio.h b/libavcodec/mpeg4audio.h
> index 8239081747..5f362e87e3 100644
> --- a/libavcodec/mpeg4audio.h
> +++ b/libavcodec/mpeg4audio.h
> @@ -45,7 +45,17 @@ extern av_export const int avpriv_mpeg4audio_sample_rates[16];
>  extern const uint8_t ff_mpeg4audio_channels[8];
>  
>  /**
> - * Parse MPEG-4 systems extradata to retrieve audio configuration.
> + * Parse MPEG-4 systems extradata from a potentially unaligned GetBitContext to retrieve audio configuration.
> + * @param[in] c        MPEG4AudioConfig structure to fill.
> + * @param[in] gb       Extradata from container.
> + * @param[in] sync_extension look for a sync extension after config if true.
> + * @return On error -1 is returned, on success AudioSpecificConfig bit index in extradata.
> + */
> +int avpriv_mpeg4audio_get_config_gb(MPEG4AudioConfig *c, GetBitContext *gb,
> +                                    int sync_extension);
> +
> +/**
> + * Parse MPEG-4 systems extradata from a raw buffer to retrieve audio configuration.
>   * @param[in] c        MPEG4AudioConfig structure to fill.
>   * @param[in] buf      Extradata from container.
>   * @param[in] bit_size Extradata size in bits.
> -- 2.11.0.483.g087da7b7c-goog