[FFmpeg-soc] extension of ac3 parser

[Michael Niedermayer]

On Sun, Apr 20, 2008 at 05:55:17PM +0200, Bartlomiej Wolowiec wrote:
> On niedziela, 20 kwietnia 2008, Michael Niedermayer wrote:
> > Please send seperate patches for seperate things.
> >
> > * adding ff_ac3_parse_channels_info()
> > * adding read_channel_map to ff_ac3_parse_header()
> > * adding parse_header()
> >
> > PS: yes i will not review them unless they are split. Ive tried this
> > with your previous patch as you refused to properly split it but it
> > didnt work out it just got more buggy in each iteration.
> >
> > [...]
> 
> Ok, I will split patch. This is the first part:
> adding read_channel_map to ff_ac3_parse_header()

[...]
> Index: libavcodec/ac3tab.c
> ===================================================================
> --- libavcodec/ac3tab.c	(wersja 12910)
> +++ libavcodec/ac3tab.c	(kopia robocza)
> @@ -247,3 +247,20 @@
>      1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 3, 3,
>      3, 6, 6, 6, 6, 6, 6, 12, 12, 12, 12, 24, 24, 24, 24, 24
>  };
> +

> +/**
> + * Default channel map for a dependent substream defined by acmod
> + */
> +const uint16_t ff_eac3_default_chmap[8] = {
> +    AC3_CHMAP_LEFT | AC3_CHMAP_RIGHT, // FIXME Ch1+Ch2
> +    AC3_CHMAP_CENTER,
> +    AC3_CHMAP_LEFT | AC3_CHMAP_RIGHT,
> +    AC3_CHMAP_LEFT | AC3_CHMAP_CENTER | AC3_CHMAP_RIGHT,

vertical align (yes ignore 80chars per line)

AC3_CHMAP_LEFT                    | AC3_CHMAP_RIGHT, // FIXME Ch1+Ch2
                 AC3_CHMAP_CENTER,
AC3_CHMAP_LEFT                    | AC3_CHMAP_RIGHT,
AC3_CHMAP_LEFT | AC3_CHMAP_CENTER | AC3_CHMAP_RIGHT,



[...]
> +/** Custom channel map locations bitmask
> + *  Other channels described in documentation:
> + *      Lc/Rc pair, Lrs/Rrs pair, Ts, Lsd/Rsd pair,
> + *      Lw/Rw pair, Lvh/Rvh pair, Cvh, Reserved, LFE2
> + */
> +enum CustomChannelMapLocation{
> +    AC3_CHMAP_LEFT =            1<<(15-0),
> +    AC3_CHMAP_CENTER =          1<<(15-1),
> +    AC3_CHMAP_RIGHT =           1<<(15-2),
> +    AC3_CHMAP_LEFT_SURROUND =   1<<(15-3),
> +    AC3_CHMAP_RIGHT_SURROUND =  1<<(15-4),
> +    AC3_CHMAP_CENTER_SURROUND = 1<<(15-7),
> +    AC3_CHMAP_LFE =             1<<(15-15)
> +};

abbreviate these a little please
..._L
..._R
..._C
..._L_SUR
..._R_SUR
..._LFE

are clear IMHO


[...]
> @@ -118,6 +123,30 @@
>          hdr->bit_rate = (uint32_t)(8.0 * hdr->frame_size * hdr->sample_rate /
>                          (num_blocks * 256.0));
>          hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
> +
> +        if(read_channel_map){
> +            int i;
> +            skip_bits(&gbc, 5); // skip bitstream id
> +
> +            /* skip dialog normalization and compression gain */
> +            for (i = 0; i < (hdr->channel_mode ? 1 : 2); i++) {
> +                skip_bits(&gbc, 5); // skip dialog normalization
> +                if (get_bits1(&gbc)) {
> +                    skip_bits(&gbc, 8); //skip Compression gain word
> +                }
> +            }
> +            /* dependent stream channel map */
> +            if (hdr->frame_type == EAC3_FRAME_TYPE_DEPENDENT && get_bits1(&gbc)) {

> +                    uint16_t tmp;

useless variable

> +                    tmp = get_bits(&gbc, 16); //custom channel map
> +                    hdr->channel_map = tmp;

[...]
> Index: libavcodec/ac3_parser.h
> ===================================================================
> --- libavcodec/ac3_parser.h	(wersja 12910)
> +++ libavcodec/ac3_parser.h	(kopia robocza)
> @@ -35,14 +35,15 @@
>  
>  /**
>   * Parses AC-3 frame header.
> - * Parses the header up to the lfeon element, which is the first 52 or 54 bits
> - * depending on the audio coding mode.
> + * Parses the header up to the lfeon element, which is the first 52, 54, or 104 bits
> + * depending on the audio coding mode and read_channel_map.
>   * @param buf[in] Array containing the first 7 bytes of the frame.
                                                ^^^^^^^

7 bytes and 104 bits ?


>   * @param hdr[out] Pointer to struct where header info is written.

> + * @param read_channel_map[in] Determines whether channel_map is to be set

why is this conditional and not always done?

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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