[FFmpeg-devel] [PATCH] Musepack SV8 demuxer and decoder

[Michael Niedermayer]

Hi

On Fri, Nov 02, 2007 at 09:58:59AM +0200, Kostya wrote:
> Here is $subj. I will try to provide samples soon.

[...]

> +	code = get_bits(gb, mpc8_cnk_len[k-1][n-1] - 1);
> +
> +	if (code >= mpc8_cnk_lost[k-1][n-1])
> +		code = ((code << 1) | get_bits1(gb)) - mpc8_cnk_lost[k-1][n-1];

duplicate


> +
> +	do {
> +		n--;
> +		if (code >= C[n]) {
> +			bits |= 1 << n;
> +			code -= C[n];
> +			C -= 32;
> +			k--;
> +		}
> +	} while(k > 0);

interresting way to store bits


[...]
> +        bands[maxband - 1].res[0] = get_vlc2(gb, res_vlc[0].table, MPC8_RES_BITS, 2);
> +        bands[maxband - 1].res[1] = get_vlc2(gb, res_vlc[0].table, MPC8_RES_BITS, 2);
> +        if(bands[maxband - 1].res[0] > 15) bands[maxband - 1].res[0] -= 17;
> +        if(bands[maxband - 1].res[1] > 15) bands[maxband - 1].res[1] -= 17;
> +        for(i = maxband - 2; i >= 0; i--){
> +            bands[i].res[0] = get_vlc2(gb, res_vlc[bands[i+1].res[0] > 2].table, MPC8_RES_BITS, 2) + bands[i + 1].res[0];
> +            bands[i].res[1] = get_vlc2(gb, res_vlc[bands[i+1].res[1] > 2].table, MPC8_RES_BITS, 2) + bands[i + 1].res[1];
> +            if(bands[i].res[0] > 15) bands[i].res[0] -= 17;
> +            if(bands[i].res[1] > 15) bands[i].res[1] -= 17;
> +        }

for(i = maxband - 1; i >= 0; i--){
    for(j=0; j<2; j++){
        last[j] = get_vlc2(gb, res_vlc[last[j] > 2].table, MPC8_RES_BITS, 2) + last[j];
        if(last[j] > 15) last[j] -= 17;
        bands[i].res[j]= last[j];
    }
}


[...]
> +const static uint8_t mpc8_cnk_len[16][32] =
> +{
> +	{0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5},
[...]
> +const static uint32_t mpc8_cnk_lost[16][32] =
> +{
> +	{0, 0, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0},
[...]
> +static const uint8_t mpc8_log2[32] =
> +{ 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5};
> +
> +static const uint8_t mpc8_log2_lost[32] =
> +{ 0, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 31};

these are nearly duplicate maybe you could change the code a little so
only 1 would be needed


[...]
> +static const uint16_t mpc8_q6_codes[2][MPC8_Q6_SIZE] = {
> +{
> + 0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0005, 0x0004, 0x0003,
> + 0x0004, 0x0005, 0x0005, 0x0006, 0x0004, 0x0005, 0x0004, 0x0003,
> + 0x0005, 0x0006, 0x0007, 0x0007, 0x0006, 0x0007, 0x0008, 0x0009,
> + 0x0005, 0x0006, 0x0007, 0x0004, 0x0005, 0x0006, 0x0007,
> +},
> +{
> + 0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0004, 0x0005, 0x0004,
> + 0x0005, 0x0006, 0x0005, 0x0006, 0x0007, 0x0008, 0x0009, 0x000A,
> + 0x000B, 0x000C, 0x000D, 0x000E, 0x000F, 0x0007, 0x0008, 0x0009,
> + 0x0006, 0x0007, 0x0005, 0x0006, 0x0007, 0x0002, 0x0003,
> +}
> +};

this and several other tabels fit in 8bit


[...]
> +/* shamelessly stolen from nutdec.c */
> +static uint64_t get_v(ByteIOContext *bc){

code duplication

[...]
> +static void mpc8_parse_seektable(AVFormatContext *s, int64_t off)
> +{
> +    MPCContext *c = s->priv_data;
> +    int tag;
> +    int64_t size, pos, ppos[2];
> +    uint8_t *buf;
> +    int i, t, seekd;
> +    GetBitContext gb;
> +
> +    url_fseek(&s->pb, off, SEEK_SET);
> +    mpc8_get_chunk_header(&s->pb, &tag, &size);
> +    if(tag != TAG_SEEKTABLE){
> +        av_log(s, AV_LOG_ERROR, "No seek table at given position\n");
> +        return;
> +    }
> +    if(!(buf = av_malloc(size)))
> +        return;
> +    get_buffer(&s->pb, buf, size);
> +    init_get_bits(&gb, buf, size * 8);
> +    size = gb_get_v(&gb);

check size please

[...]
> +    s->start_time = 0;
> +    s->duration = c->samples * AV_TIME_BASE / st->codec->sample_rate;

    /** decoding: position of the first frame of the component, in
       AV_TIME_BASE fractional seconds. NEVER set this value directly:
                                        ^^^^^ 
       it is deduced from the AVStream values.  */
    int64_t start_time;
    /** decoding: duration of the stream, in AV_TIME_BASE fractional
       seconds. NEVER set this value directly: it is deduced from the
                ^^^^^
       AVStream values.  */
    int64_t duration;


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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