vp3.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

    int decode_partial_blocks = 0;
    int first_c_fragment_seen;

    int i, j;
    int current_fragment;

    debug_vp3("  vp3: unpacking superblock coding\n");

    if (s->keyframe) {

        debug_vp3("    keyframe-- all superblocks are fully coded\n");
        memset(s->superblock_coding, SB_FULLY_CODED, s->superblock_count);

    } else {

        /* unpack the list of partially-coded superblocks */
        bit = get_bits1(gb);
        /* toggle the bit because as soon as the first run length is
         * fetched the bit will be toggled again */
        bit ^= 1;
        while (current_superblock < s->superblock_count) {
            if (current_run-- == 0) {
                bit ^= 1;
                current_run = get_vlc2(gb,
                    s->superblock_run_length_vlc.table, 6, 2);
                if (current_run == 33)
                    current_run += get_bits(gb, 12);
                debug_block_coding("      setting superblocks %d..%d to %s\n",
                    current_superblock,
                    current_superblock + current_run - 1,
                    (bit) ? "partially coded" : "not coded");

                /* if any of the superblocks are not partially coded, flag
                 * a boolean to decode the list of fully-coded superblocks */
                if (bit == 0) {
                    decode_fully_flags = 1;
                } else {

                    /* make a note of the fact that there are partially coded
                     * superblocks */
                    decode_partial_blocks = 1;
                }
            }
            s->superblock_coding[current_superblock++] = bit;
        }

        /* unpack the list of fully coded superblocks if any of the blocks were
         * not marked as partially coded in the previous step */
        if (decode_fully_flags) {

            current_superblock = 0;
            current_run = 0;
            bit = get_bits1(gb);
            /* toggle the bit because as soon as the first run length is
             * fetched the bit will be toggled again */
            bit ^= 1;
            while (current_superblock < s->superblock_count) {

                /* skip any superblocks already marked as partially coded */
                if (s->superblock_coding[current_superblock] == SB_NOT_CODED) {

                    if (current_run-- == 0) {
                        bit ^= 1;
                        current_run = get_vlc2(gb,
                            s->superblock_run_length_vlc.table, 6, 2);
                        if (current_run == 33)
                            current_run += get_bits(gb, 12);
                    }

                    debug_block_coding("      setting superblock %d to %s\n",
                        current_superblock,
                        (bit) ? "fully coded" : "not coded");
                    s->superblock_coding[current_superblock] = 2*bit;
                }
                current_superblock++;
            }
        }

        /* if there were partial blocks, initialize bitstream for
         * unpacking fragment codings */
        if (decode_partial_blocks) {

            current_run = 0;
            bit = get_bits1(gb);
            /* toggle the bit because as soon as the first run length is
             * fetched the bit will be toggled again */
            bit ^= 1;
        }
    }

    /* figure out which fragments are coded; iterate through each
     * superblock (all planes) */
    s->coded_fragment_list_index = 0;
    s->next_coeff= s->coeffs + s->fragment_count;
    s->first_coded_y_fragment = s->first_coded_c_fragment = 0;
    s->last_coded_y_fragment = s->last_coded_c_fragment = -1;
    first_c_fragment_seen = 0;
    memset(s->macroblock_coding, MODE_COPY, s->macroblock_count);
    for (i = 0; i < s->superblock_count; i++) {

        /* iterate through all 16 fragments in a superblock */
        for (j = 0; j < 16; j++) {

            /* if the fragment is in bounds, check its coding status */
            current_fragment = s->superblock_fragments[i * 16 + j];
            if (current_fragment >= s->fragment_count) {
                av_log(s->avctx, AV_LOG_ERROR, "  vp3:unpack_superblocks(): bad fragment number (%d >= %d)\n",
                    current_fragment, s->fragment_count);
                return 1;
            }
            if (current_fragment != -1) {
                if (s->superblock_coding[i] == SB_NOT_CODED) {

                    /* copy all the fragments from the prior frame */
                    s->all_fragments[current_fragment].coding_method =
                        MODE_COPY;

                } else if (s->superblock_coding[i] == SB_PARTIALLY_CODED) {

                    /* fragment may or may not be coded; this is the case
                     * that cares about the fragment coding runs */
                    if (current_run-- == 0) {
                        bit ^= 1;
                        current_run = get_vlc2(gb,
                            s->fragment_run_length_vlc.table, 5, 2);
                    }

                    if (bit) {
                        /* default mode; actual mode will be decoded in
                         * the next phase */
                        s->all_fragments[current_fragment].coding_method =
                            MODE_INTER_NO_MV;
                        s->all_fragments[current_fragment].next_coeff= s->coeffs + current_fragment;
                        s->coded_fragment_list[s->coded_fragment_list_index] =
                            current_fragment;
                        if ((current_fragment >= s->fragment_start[1]) &&
                            (s->last_coded_y_fragment == -1) &&
                            (!first_c_fragment_seen)) {
                            s->first_coded_c_fragment = s->coded_fragment_list_index;
                            s->last_coded_y_fragment = s->first_coded_c_fragment - 1;
                            first_c_fragment_seen = 1;
                        }
                        s->coded_fragment_list_index++;
                        s->macroblock_coding[s->all_fragments[current_fragment].macroblock] = MODE_INTER_NO_MV;
                        debug_block_coding("      superblock %d is partially coded, fragment %d is coded\n",
                            i, current_fragment);
                    } else {
                        /* not coded; copy this fragment from the prior frame */
                        s->all_fragments[current_fragment].coding_method =
                            MODE_COPY;
                        debug_block_coding("      superblock %d is partially coded, fragment %d is not coded\n",
                            i, current_fragment);
                    }

                } else {

                    /* fragments are fully coded in this superblock; actual
                     * coding will be determined in next step */
                    s->all_fragments[current_fragment].coding_method =
                        MODE_INTER_NO_MV;
                    s->all_fragments[current_fragment].next_coeff= s->coeffs + current_fragment;
                    s->coded_fragment_list[s->coded_fragment_list_index] =
                        current_fragment;
                    if ((current_fragment >= s->fragment_start[1]) &&
                        (s->last_coded_y_fragment == -1) &&
                        (!first_c_fragment_seen)) {
                        s->first_coded_c_fragment = s->coded_fragment_list_index;
                        s->last_coded_y_fragment = s->first_coded_c_fragment - 1;
                        first_c_fragment_seen = 1;
                    }
                    s->coded_fragment_list_index++;
                    s->macroblock_coding[s->all_fragments[current_fragment].macroblock] = MODE_INTER_NO_MV;
                    debug_block_coding("      superblock %d is fully coded, fragment %d is coded\n",
                        i, current_fragment);
                }
            }
        }
    }

    if (!first_c_fragment_seen)
        /* only Y fragments coded in this frame */
        s->last_coded_y_fragment = s->coded_fragment_list_index - 1;
    else
        /* end the list of coded C fragments */
        s->last_coded_c_fragment = s->coded_fragment_list_index - 1;

    debug_block_coding("    %d total coded fragments, y: %d -> %d, c: %d -> %d\n",
        s->coded_fragment_list_index,
        s->first_coded_y_fragment,
        s->last_coded_y_fragment,
        s->first_coded_c_fragment,
        s->last_coded_c_fragment);

    return 0;
}

/*
 * This function unpacks all the coding mode data for individual macroblocks
 * from the bitstream.
 */
static int unpack_modes(Vp3DecodeContext *s, GetBitContext *gb)
{
    int i, j, k;
    int scheme;
    int current_macroblock;
    int current_fragment;
    int coding_mode;

    debug_vp3("  vp3: unpacking encoding modes\n");

    if (s->keyframe) {
        debug_vp3("    keyframe-- all blocks are coded as INTRA\n");

        for (i = 0; i < s->fragment_count; i++)
            s->all_fragments[i].coding_method = MODE_INTRA;

    } else {

        /* fetch the mode coding scheme for this frame */
        scheme = get_bits(gb, 3);
        debug_modes("    using mode alphabet %d\n", scheme);

        /* is it a custom coding scheme? */
        if (scheme == 0) {
            debug_modes("    custom mode alphabet ahead:\n");
            for (i = 0; i < 8; i++)
                ModeAlphabet[scheme][get_bits(gb, 3)] = i;
        }

        for (i = 0; i < 8; i++)
            debug_modes("      mode[%d][%d] = %d\n", scheme, i,
                ModeAlphabet[scheme][i]);

        /* iterate through all of the macroblocks that contain 1 or more
         * coded fragments */
        for (i = 0; i < s->u_superblock_start; i++) {

            for (j = 0; j < 4; j++) {
                current_macroblock = s->superblock_macroblocks[i * 4 + j];
                if ((current_macroblock == -1) ||
                    (s->macroblock_coding[current_macroblock] == MODE_COPY))
                    continue;
                if (current_macroblock >= s->macroblock_count) {
                    av_log(s->avctx, AV_LOG_ERROR, "  vp3:unpack_modes(): bad macroblock number (%d >= %d)\n",
                        current_macroblock, s->macroblock_count);
                    return 1;
                }

                /* mode 7 means get 3 bits for each coding mode */
                if (scheme == 7)
                    coding_mode = get_bits(gb, 3);
                else
                    coding_mode = ModeAlphabet[scheme]
                        [get_vlc2(gb, s->mode_code_vlc.table, 3, 3)];

                s->macroblock_coding[current_macroblock] = coding_mode;
                for (k = 0; k < 6; k++) {
                    current_fragment =
                        s->macroblock_fragments[current_macroblock * 6 + k];
                    if (current_fragment == -1)
                        continue;
                    if (current_fragment >= s->fragment_count) {
                        av_log(s->avctx, AV_LOG_ERROR, "  vp3:unpack_modes(): bad fragment number (%d >= %d)\n",
                            current_fragment, s->fragment_count);
                        return 1;
                    }
                    if (s->all_fragments[current_fragment].coding_method !=
                        MODE_COPY)
                        s->all_fragments[current_fragment].coding_method =
                            coding_mode;
                }

                debug_modes("    coding method for macroblock starting @ fragment %d = %d\n",
                    s->macroblock_fragments[current_macroblock * 6], coding_mode);
            }
        }
    }

    return 0;
}

/*
 * This function unpacks all the motion vectors for the individual
 * macroblocks from the bitstream.
 */
static int unpack_vectors(Vp3DecodeContext *s, GetBitContext *gb)
{
    int i, j, k;
    int coding_mode;
    int motion_x[6];
    int motion_y[6];
    int last_motion_x = 0;
    int last_motion_y = 0;
    int prior_last_motion_x = 0;
    int prior_last_motion_y = 0;
    int current_macroblock;
    int current_fragment;

    debug_vp3("  vp3: unpacking motion vectors\n");
    if (s->keyframe) {

        debug_vp3("    keyframe-- there are no motion vectors\n");

    } else {

        memset(motion_x, 0, 6 * sizeof(int));
        memset(motion_y, 0, 6 * sizeof(int));

        /* coding mode 0 is the VLC scheme; 1 is the fixed code scheme */
        coding_mode = get_bits1(gb);
        debug_vectors("    using %s scheme for unpacking motion vectors\n",
            (coding_mode == 0) ? "VLC" : "fixed-length");

        /* iterate through all of the macroblocks that contain 1 or more
         * coded fragments */
        for (i = 0; i < s->u_superblock_start; i++) {

            for (j = 0; j < 4; j++) {
                current_macroblock = s->superblock_macroblocks[i * 4 + j];
                if ((current_macroblock == -1) ||
                    (s->macroblock_coding[current_macroblock] == MODE_COPY))
                    continue;
                if (current_macroblock >= s->macroblock_count) {
                    av_log(s->avctx, AV_LOG_ERROR, "  vp3:unpack_vectors(): bad macroblock number (%d >= %d)\n",
                        current_macroblock, s->macroblock_count);
                    return 1;
                }

                current_fragment = s->macroblock_fragments[current_macroblock * 6];
                if (current_fragment >= s->fragment_count) {
                    av_log(s->avctx, AV_LOG_ERROR, "  vp3:unpack_vectors(): bad fragment number (%d >= %d\n",
                        current_fragment, s->fragment_count);
                    return 1;
                }
                switch (s->macroblock_coding[current_macroblock]) {