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/*

 * H261 decoder

 * Copyright (c) 2002-2004 Michael Niedermayer 

 * Copyright (c) 2004 Maarten Daniels

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * FFmpeg is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file

 * H.261 decoder.

 */

#include "libavutil/avassert.h"

#include "avcodec.h"

#include "mpegvideo.h"

#include "h263.h"

#include "h261.h"

#define H261_MBA_VLC_BITS 9

#define H261_MTYPE_VLC_BITS 6

#define H261_MV_VLC_BITS 7

#define H261_CBP_VLC_BITS 9

#define TCOEFF_VLC_BITS 9

#define MBA_STUFFING 33

#define MBA_STARTCODE 34

static VLC h261_mba_vlc;

static VLC h261_mtype_vlc;

static VLC h261_mv_vlc;

static VLC h261_cbp_vlc;

static av_cold void h261_decode_init_vlc(H261Context *h)

{

    static int done = 0;

    if (!done) {

        done = 1;

        INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,

                        ff_h261_mba_bits, 1, 1,

                        ff_h261_mba_code, 1, 1, 662);

        INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,

                        ff_h261_mtype_bits, 1, 1,

                        ff_h261_mtype_code, 1, 1, 80);

        INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,

                        &ff_h261_mv_tab[0][1], 2, 1,

                        &ff_h261_mv_tab[0][0], 2, 1, 144);

        INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,

                        &ff_h261_cbp_tab[0][1], 2, 1,

                        &ff_h261_cbp_tab[0][0], 2, 1, 512);

        INIT_VLC_RL(ff_h261_rl_tcoeff, 552);

    }

}

static av_cold int h261_decode_init(AVCodecContext *avctx)

{

    H261Context *h          = avctx->priv_data;

    MpegEncContext *const s = &h->s;

    // set defaults

    ff_MPV_decode_defaults(s);

    s->avctx       = avctx;

    s->width       = s->avctx->coded_width;

    s->height      = s->avctx->coded_height;

    s->codec_id    = s->avctx->codec->id;

    s->out_format  = FMT_H261;

    s->low_delay   = 1;

    avctx->pix_fmt = AV_PIX_FMT_YUV420P;

    s->codec_id    = avctx->codec->id;

    ff_h261_common_init();

    h261_decode_init_vlc(h);

    h->gob_start_code_skipped = 0;

    return 0;

}

/**

 * Decode the group of blocks header or slice header.

 * @return <0 if an error occurred

 */

static int h261_decode_gob_header(H261Context *h)

{

    unsigned int val;

    MpegEncContext *const s = &h->s;

    if (!h->gob_start_code_skipped) {

        /* Check for GOB Start Code */

        val = show_bits(&s->gb, 15);

        if (val)

            return -1;

        /* We have a GBSC */

        skip_bits(&s->gb, 16);

    }

    h->gob_start_code_skipped = 0;

    h->gob_number = get_bits(&s->gb, 4); /* GN */

    s->qscale     = get_bits(&s->gb, 5); /* GQUANT */

    /* Check if gob_number is valid */

    if (s->mb_height == 18) { // CIF

        if ((h->gob_number <= 0) || (h->gob_number > 12))

            return -1;

    } else { // QCIF

        if ((h->gob_number != 1) && (h->gob_number != 3) &&

            (h->gob_number != 5))

            return -1;

    }

    /* GEI */

    while (get_bits1(&s->gb) != 0)

        skip_bits(&s->gb, 8);

    if (s->qscale == 0) {

        av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");

        if (s->avctx->err_recognition & (AV_EF_BITSTREAM | AV_EF_COMPLIANT))

            return -1;

    }

    /* For the first transmitted macroblock in a GOB, MBA is the absolute

     * address. For subsequent macroblocks, MBA is the difference between

     * the absolute addresses of the macroblock and the last transmitted

     * macroblock. */

    h->current_mba = 0;

    h->mba_diff    = 0;

    return 0;

}

/**

 * Decode the group of blocks / video packet header.

 * @return <0 if no resync found

 */

static int h261_resync(H261Context *h)

{

    MpegEncContext *const s = &h->s;

    int left, ret;

    if (h->gob_start_code_skipped) {

        ret = h261_decode_gob_header(h);

        if (ret >= 0)

            return 0;

    } else {

        if (show_bits(&s->gb, 15) == 0) {

            ret = h261_decode_gob_header(h);

            if (ret >= 0)

                return 0;

        }

        // OK, it is not where it is supposed to be ...

        s->gb = s->last_resync_gb;

        align_get_bits(&s->gb);

        left = get_bits_left(&s->gb);

        for (; left > 15 + 1 + 4 + 5; left -= 8) {

            if (show_bits(&s->gb, 15) == 0) {

                GetBitContext bak = s->gb;

                ret = h261_decode_gob_header(h);

                if (ret >= 0)

                    return 0;

                s->gb = bak;

            }

            skip_bits(&s->gb, 8);

        }

    }

    return -1;

}

/**

 * Decode skipped macroblocks.

 * @return 0

 */

static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2)

{

    MpegEncContext *const s = &h->s;

    int i;

    s->mb_intra = 0;

    for (i = mba1; i < mba2; i++) {

        int j, xy;

        s->mb_x = ((h->gob_number - 1) % 2) * 11 + i % 11;

        s->mb_y = ((h->gob_number - 1) / 2) * 3 + i / 11;

        xy      = s->mb_x + s->mb_y * s->mb_stride;

        ff_init_block_index(s);

        ff_update_block_index(s);

        for (j = 0; j < 6; j++)

            s->block_last_index[j] = -1;

        s->mv_dir                      = MV_DIR_FORWARD;

        s->mv_type                     = MV_TYPE_16X16;

        s->current_picture.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;

        s->mv[0][0][0]                 = 0;

        s->mv[0][0][1]                 = 0;

        s->mb_skipped                  = 1;

        h->mtype                      &= ~MB_TYPE_H261_FIL;

        ff_MPV_decode_mb(s, s->block);

    }

    return 0;

}

static const int mvmap[17] = {

    0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16

};

static int decode_mv_component(GetBitContext *gb, int v)

{

    int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);

    /* check if mv_diff is valid */

    if (mv_diff < 0)

        return v;

    mv_diff = mvmap[mv_diff];

    if (mv_diff && !get_bits1(gb))

        mv_diff = -mv_diff;

    v += mv_diff;

    if (v <= -16)

        v += 32;

    else if (v >= 16)

        v -= 32;

    return v;

}

/**

 * Decode a macroblock.

 * @return <0 if an error occurred

 */

static int h261_decode_block(H261Context *h, int16_t *block, int n, int coded)

{

    MpegEncContext *const s = &h->s;

    int code, level, i, j, run;

    RLTable *rl = &ff_h261_rl_tcoeff;

    const uint8_t *scan_table;

    /* For the variable length encoding there are two code tables, one being

     * used for the first transmitted LEVEL in INTER, INTER + MC and

     * INTER + MC + FIL blocks, the second for all other LEVELs except the

     * first one in INTRA blocks which is fixed length coded with 8 bits.

     * NOTE: The two code tables only differ in one VLC so we handle that

     * manually. */

    scan_table = s->intra_scantable.permutated;

    if (s->mb_intra) {

        /* DC coef */

        level = get_bits(&s->gb, 8);

        // 0 (00000000b) and -128 (10000000b) are FORBIDDEN

        if ((level & 0x7F) == 0) {

            av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n",

                   level, s->mb_x, s->mb_y);

            return -1;

        }

        /* The code 1000 0000 is not used, the reconstruction level of 1024

         * being coded as 1111 1111. */

        if (level == 255)

            level = 128;

        block[0] = level;

        i        = 1;

    } else if (coded) {

        // Run  Level   Code

        // EOB          Not possible for first level when cbp is available (that's why the table is different)

        // 0    1       1s

        // *    *       0*

        int check = show_bits(&s->gb, 2);

        i = 0;

        if (check & 0x2) {

            skip_bits(&s->gb, 2);

            block[0] = (check & 0x1) ? -1 : 1;

            i        = 1;

        }

    } else {

        i = 0;

    }

    if (!coded) {

        s->block_last_index[n] = i - 1;

        return 0;

    }

    for (;;) {

        code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);

        if (code < 0) {

            av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",

                   s->mb_x, s->mb_y);

            return -1;

        }

        if (code == rl->n) {

            /* escape */

            /* The remaining combinations of (run, level) are encoded with a

             * 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits

             * level. */

            run   = get_bits(&s->gb, 6);

            level = get_sbits(&s->gb, 8);

        } else if (code == 0) {

            break;

        } else {

            run   = rl->table_run[code];

            level = rl->table_level[code];

            if (get_bits1(&s->gb))

                level = -level;

        }

        i += run;

        if (i >= 64) {

            av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",

                   s->mb_x, s->mb_y);

            return -1;

        }

        j        = scan_table[i];

        block[j] = level;

        i++;

    }

    s->block_last_index[n] = i - 1;

    return 0;

}

static int h261_decode_mb(H261Context *h)

{

    MpegEncContext *const s = &h->s;

    int i, cbp, xy;

    cbp = 63;

    // Read mba

    do {

        h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,

                               H261_MBA_VLC_BITS, 2);

        /* Check for slice end */

        /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */

        if (h->mba_diff == MBA_STARTCODE) { // start code

            h->gob_start_code_skipped = 1;

            return SLICE_END;

        }

    } while (h->mba_diff == MBA_STUFFING); // stuffing

    if (h->mba_diff < 0) {

        if (get_bits_left(&s->gb) <= 7)

            return SLICE_END;

        av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);

        return SLICE_ERROR;

    }

    h->mba_diff    += 1;

    h->current_mba += h->mba_diff;

    if (h->current_mba > MBA_STUFFING)

        return SLICE_ERROR;

    s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);

    s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);

    xy      = s->mb_x + s->mb_y * s->mb_stride;

    ff_init_block_index(s);

    ff_update_block_index(s);

    // Read mtype

    h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);

    if (h->mtype < 0) {

        av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index %d\n",

               h->mtype);

        return SLICE_ERROR;

    }

    av_assert0(h->mtype < FF_ARRAY_ELEMS(ff_h261_mtype_map));

    h->mtype = ff_h261_mtype_map[h->mtype];

    // Read mquant

    if (IS_QUANT(h->mtype))

        ff_set_qscale(s, get_bits(&s->gb, 5));

    s->mb_intra = IS_INTRA4x4(h->mtype);

    // Read mv

    if (IS_16X16(h->mtype)) {

        /* Motion vector data is included for all MC macroblocks. MVD is

         * obtained from the macroblock vector by subtracting the vector

         * of the preceding macroblock. For this calculation the vector

         * of the preceding macroblock is regarded as zero in the

         * following three situations:

         * 1) evaluating MVD for macroblocks 1, 12 and 23;

         * 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;

         * 3) MTYPE of the previous macroblock was not MC. */

        if ((h->current_mba ==  1) || (h->current_mba == 12) ||

            (h->current_mba == 23) || (h->mba_diff != 1)) {

            h->current_mv_x = 0;

            h->current_mv_y = 0;

        }

        h->current_mv_x = decode_mv_component(&s->gb, h->current_mv_x);

        h->current_mv_y = decode_mv_component(&s->gb, h->current_mv_y);

    } else {

        h->current_mv_x = 0;

        h->current_mv_y = 0;

    }

    // Read cbp

    if (HAS_CBP(h->mtype))

        cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;

    if (s->mb_intra) {

        s->current_picture.mb_type[xy] = MB_TYPE_INTRA;

        goto intra;

    }

    //set motion vectors

    s->mv_dir                      = MV_DIR_FORWARD;

    s->mv_type                     = MV_TYPE_16X16;

    s->current_picture.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;

    s->mv[0][0][0]                 = h->current_mv_x * 2; // gets divided by 2 in motion compensation

    s->mv[0][0][1]                 = h->current_mv_y * 2;

intra:

    /* decode each block */

    if (s->mb_intra || HAS_CBP(h->mtype)) {

        s->dsp.clear_blocks(s->block[0]);

        for (i = 0; i < 6; i++) {

            if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)

                return SLICE_ERROR;

            cbp += cbp;

        }

    } else {

        for (i = 0; i < 6; i++)

            s->block_last_index[i] = -1;

    }

    ff_MPV_decode_mb(s, s->block);

    return SLICE_OK;

}

/**

 * Decode the H.261 picture header.

 * @return <0 if no startcode found

 */

static int h261_decode_picture_header(H261Context *h)

{

    MpegEncContext *const s = &h->s;

    int format, i;

    uint32_t startcode = 0;

    for (i = get_bits_left(&s->gb); i > 24; i -= 1) {

        startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;

        if (startcode == 0x10)

            break;

    }

    if (startcode != 0x10) {

        av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");

        return -1;

    }

    /* temporal reference */

    i = get_bits(&s->gb, 5); /* picture timestamp */

    if (i < (s->picture_number & 31))

        i += 32;

    s->picture_number = (s->picture_number & ~31) + i;

    s->avctx->time_base      = (AVRational) { 1001, 30000 };

    s->current_picture.f.pts = s->picture_number;

    /* PTYPE starts here */

    skip_bits1(&s->gb); /* split screen off */

    skip_bits1(&s->gb); /* camera  off */

    skip_bits1(&s->gb); /* freeze picture release off */

    format = get_bits1(&s->gb);

    // only 2 formats possible

    if (format == 0) { // QCIF

        s->width     = 176;

        s->height    = 144;

        s->mb_width  = 11;

        s->mb_height = 9;

    } else { // CIF

        s->width     = 352;

        s->height    = 288;

        s->mb_width  = 22;

        s->mb_height = 18;

    }

    s->mb_num = s->mb_width * s->mb_height;

    skip_bits1(&s->gb); /* still image mode off */

    skip_bits1(&s->gb); /* Reserved */

    /* PEI */

    while (get_bits1(&s->gb) != 0)

        skip_bits(&s->gb, 8);

    /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first

     * frame, the codec crashes if it does not contain all I-blocks

     * (e.g. when a packet is lost). */

    s->pict_type = AV_PICTURE_TYPE_P;

    h->gob_number = 0;

    return 0;

}

static int h261_decode_gob(H261Context *h)

{

    MpegEncContext *const s = &h->s;

    ff_set_qscale(s, s->qscale);

    /* decode mb's */

    while (h->current_mba <= MBA_STUFFING) {

        int ret;

        /* DCT & quantize */

        ret = h261_decode_mb(h);

        if (ret < 0) {

            if (ret == SLICE_END) {

                h261_decode_mb_skipped(h, h->current_mba, 33);

                return 0;

            }

            av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",

                   s->mb_x + s->mb_y * s->mb_stride);

            return -1;

        }

        h261_decode_mb_skipped(h,

                               h->current_mba - h->mba_diff,

                               h->current_mba - 1);

    }

    return -1;

}

/**

 * returns the number of bytes consumed for building the current frame

 */

static int get_consumed_bytes(MpegEncContext *s, int buf_size)

{

    int pos = get_bits_count(&s->gb) >> 3;

    if (pos == 0)

        pos = 1;      // avoid infinite loops (i doubt that is needed but ...)

    if (pos + 10 > buf_size)

        pos = buf_size;               // oops ;)

    return pos;

}

static int h261_decode_frame(AVCodecContext *avctx, void *data,

                             int *got_frame, AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size       = avpkt->size;

    H261Context *h     = avctx->priv_data;

    MpegEncContext *s  = &h->s;

    int ret;

    AVFrame *pict = data;

    av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);

    av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);

    s->flags  = avctx->flags;

    s->flags2 = avctx->flags2;

    h->gob_start_code_skipped = 0;

retry:

    init_get_bits(&s->gb, buf, buf_size * 8);

    if (!s->context_initialized)

        // we need the IDCT permutaton for reading a custom matrix

        if (ff_MPV_common_init(s) < 0)

            return -1;

    /* We need to set current_picture_ptr before reading the header,

     * otherwise we cannot store anything in there. */

    if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {

        int i = ff_find_unused_picture(s, 0);

        if (i < 0)

            return i;

        s->current_picture_ptr = &s->picture[i];

    }

    ret = h261_decode_picture_header(h);

    /* skip if the header was thrashed */

    if (ret < 0) {

        av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");

        return -1;

    }

    if (s->width != avctx->coded_width || s->height != avctx->coded_height) {

        ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat

        s->parse_context.buffer = 0;

        ff_MPV_common_end(s);

        s->parse_context = pc;

    }

    if (!s->context_initialized) {

        avcodec_set_dimensions(avctx, s->width, s->height);

        goto retry;

    }

    // for skipping the frame

    s->current_picture.f.pict_type = s->pict_type;

    s->current_picture.f.key_frame = s->pict_type == AV_PICTURE_TYPE_I;

    if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||

        (avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type != AV_PICTURE_TYPE_I) ||

         avctx->skip_frame >= AVDISCARD_ALL)

        return get_consumed_bytes(s, buf_size);

    if (ff_MPV_frame_start(s, avctx) < 0)

        return -1;

    ff_mpeg_er_frame_start(s);

    /* decode each macroblock */

    s->mb_x = 0;

    s->mb_y = 0;

    while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {

        if (h261_resync(h) < 0)

            break;

        h261_decode_gob(h);

    }

    ff_MPV_frame_end(s);

    av_assert0(s->current_picture.f.pict_type == s->current_picture_ptr->f.pict_type);

    av_assert0(s->current_picture.f.pict_type == s->pict_type);

    if ((ret = av_frame_ref(pict, &s->current_picture_ptr->f)) < 0)

        return ret;

    ff_print_debug_info(s, s->current_picture_ptr, pict);

    *got_frame = 1;

    return get_consumed_bytes(s, buf_size);

}

static av_cold int h261_decode_end(AVCodecContext *avctx)

{

    H261Context *h    = avctx->priv_data;

    MpegEncContext *s = &h->s;

    ff_MPV_common_end(s);

    return 0;

}

AVCodec ff_h261_decoder = {

    .name           = "h261",

    .long_name      = NULL_IF_CONFIG_SMALL("H.261"),

    .type           = AVMEDIA_TYPE_VIDEO,

    .id             = AV_CODEC_ID_H261,

    .priv_data_size = sizeof(H261Context),

    .init           = h261_decode_init,

    .close          = h261_decode_end,

    .decode         = h261_decode_frame,

    .capabilities   = CODEC_CAP_DR1,

    .max_lowres     = 3,

};