yading@10: /*
yading@10:  * H261 decoder
yading@10:  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
yading@10:  * Copyright (c) 2004 Maarten Daniels
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * H.261 decoder.
yading@10:  */
yading@10: 
yading@10: #include "libavutil/avassert.h"
yading@10: #include "avcodec.h"
yading@10: #include "mpegvideo.h"
yading@10: #include "h263.h"
yading@10: #include "h261.h"
yading@10: 
yading@10: #define H261_MBA_VLC_BITS 9
yading@10: #define H261_MTYPE_VLC_BITS 6
yading@10: #define H261_MV_VLC_BITS 7
yading@10: #define H261_CBP_VLC_BITS 9
yading@10: #define TCOEFF_VLC_BITS 9
yading@10: #define MBA_STUFFING 33
yading@10: #define MBA_STARTCODE 34
yading@10: 
yading@10: static VLC h261_mba_vlc;
yading@10: static VLC h261_mtype_vlc;
yading@10: static VLC h261_mv_vlc;
yading@10: static VLC h261_cbp_vlc;
yading@10: 
yading@10: static av_cold void h261_decode_init_vlc(H261Context *h)
yading@10: {
yading@10:     static int done = 0;
yading@10: 
yading@10:     if (!done) {
yading@10:         done = 1;
yading@10:         INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
yading@10:                         ff_h261_mba_bits, 1, 1,
yading@10:                         ff_h261_mba_code, 1, 1, 662);
yading@10:         INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
yading@10:                         ff_h261_mtype_bits, 1, 1,
yading@10:                         ff_h261_mtype_code, 1, 1, 80);
yading@10:         INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
yading@10:                         &ff_h261_mv_tab[0][1], 2, 1,
yading@10:                         &ff_h261_mv_tab[0][0], 2, 1, 144);
yading@10:         INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
yading@10:                         &ff_h261_cbp_tab[0][1], 2, 1,
yading@10:                         &ff_h261_cbp_tab[0][0], 2, 1, 512);
yading@10:         INIT_VLC_RL(ff_h261_rl_tcoeff, 552);
yading@10:     }
yading@10: }
yading@10: 
yading@10: static av_cold int h261_decode_init(AVCodecContext *avctx)
yading@10: {
yading@10:     H261Context *h          = avctx->priv_data;
yading@10:     MpegEncContext *const s = &h->s;
yading@10: 
yading@10:     // set defaults
yading@10:     ff_MPV_decode_defaults(s);
yading@10:     s->avctx       = avctx;
yading@10:     s->width       = s->avctx->coded_width;
yading@10:     s->height      = s->avctx->coded_height;
yading@10:     s->codec_id    = s->avctx->codec->id;
yading@10:     s->out_format  = FMT_H261;
yading@10:     s->low_delay   = 1;
yading@10:     avctx->pix_fmt = AV_PIX_FMT_YUV420P;
yading@10:     s->codec_id    = avctx->codec->id;
yading@10: 
yading@10:     ff_h261_common_init();
yading@10:     h261_decode_init_vlc(h);
yading@10: 
yading@10:     h->gob_start_code_skipped = 0;
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Decode the group of blocks header or slice header.
yading@10:  * @return <0 if an error occurred
yading@10:  */
yading@10: static int h261_decode_gob_header(H261Context *h)
yading@10: {
yading@10:     unsigned int val;
yading@10:     MpegEncContext *const s = &h->s;
yading@10: 
yading@10:     if (!h->gob_start_code_skipped) {
yading@10:         /* Check for GOB Start Code */
yading@10:         val = show_bits(&s->gb, 15);
yading@10:         if (val)
yading@10:             return -1;
yading@10: 
yading@10:         /* We have a GBSC */
yading@10:         skip_bits(&s->gb, 16);
yading@10:     }
yading@10: 
yading@10:     h->gob_start_code_skipped = 0;
yading@10: 
yading@10:     h->gob_number = get_bits(&s->gb, 4); /* GN */
yading@10:     s->qscale     = get_bits(&s->gb, 5); /* GQUANT */
yading@10: 
yading@10:     /* Check if gob_number is valid */
yading@10:     if (s->mb_height == 18) { // CIF
yading@10:         if ((h->gob_number <= 0) || (h->gob_number > 12))
yading@10:             return -1;
yading@10:     } else { // QCIF
yading@10:         if ((h->gob_number != 1) && (h->gob_number != 3) &&
yading@10:             (h->gob_number != 5))
yading@10:             return -1;
yading@10:     }
yading@10: 
yading@10:     /* GEI */
yading@10:     while (get_bits1(&s->gb) != 0)
yading@10:         skip_bits(&s->gb, 8);
yading@10: 
yading@10:     if (s->qscale == 0) {
yading@10:         av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
yading@10:         if (s->avctx->err_recognition & (AV_EF_BITSTREAM | AV_EF_COMPLIANT))
yading@10:             return -1;
yading@10:     }
yading@10: 
yading@10:     /* For the first transmitted macroblock in a GOB, MBA is the absolute
yading@10:      * address. For subsequent macroblocks, MBA is the difference between
yading@10:      * the absolute addresses of the macroblock and the last transmitted
yading@10:      * macroblock. */
yading@10:     h->current_mba = 0;
yading@10:     h->mba_diff    = 0;
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Decode the group of blocks / video packet header.
yading@10:  * @return <0 if no resync found
yading@10:  */
yading@10: static int ff_h261_resync(H261Context *h)
yading@10: {
yading@10:     MpegEncContext *const s = &h->s;
yading@10:     int left, ret;
yading@10: 
yading@10:     if (h->gob_start_code_skipped) {
yading@10:         ret = h261_decode_gob_header(h);
yading@10:         if (ret >= 0)
yading@10:             return 0;
yading@10:     } else {
yading@10:         if (show_bits(&s->gb, 15) == 0) {
yading@10:             ret = h261_decode_gob_header(h);
yading@10:             if (ret >= 0)
yading@10:                 return 0;
yading@10:         }
yading@10:         // OK, it is not where it is supposed to be ...
yading@10:         s->gb = s->last_resync_gb;
yading@10:         align_get_bits(&s->gb);
yading@10:         left = get_bits_left(&s->gb);
yading@10: 
yading@10:         for (; left > 15 + 1 + 4 + 5; left -= 8) {
yading@10:             if (show_bits(&s->gb, 15) == 0) {
yading@10:                 GetBitContext bak = s->gb;
yading@10: 
yading@10:                 ret = h261_decode_gob_header(h);
yading@10:                 if (ret >= 0)
yading@10:                     return 0;
yading@10: 
yading@10:                 s->gb = bak;
yading@10:             }
yading@10:             skip_bits(&s->gb, 8);
yading@10:         }
yading@10:     }
yading@10: 
yading@10:     return -1;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Decode skipped macroblocks.
yading@10:  * @return 0
yading@10:  */
yading@10: static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2)
yading@10: {
yading@10:     MpegEncContext *const s = &h->s;
yading@10:     int i;
yading@10: 
yading@10:     s->mb_intra = 0;
yading@10: 
yading@10:     for (i = mba1; i < mba2; i++) {
yading@10:         int j, xy;
yading@10: 
yading@10:         s->mb_x = ((h->gob_number - 1) % 2) * 11 + i % 11;
yading@10:         s->mb_y = ((h->gob_number - 1) / 2) * 3 + i / 11;
yading@10:         xy      = s->mb_x + s->mb_y * s->mb_stride;
yading@10:         ff_init_block_index(s);
yading@10:         ff_update_block_index(s);
yading@10: 
yading@10:         for (j = 0; j < 6; j++)
yading@10:             s->block_last_index[j] = -1;
yading@10: 
yading@10:         s->mv_dir                      = MV_DIR_FORWARD;
yading@10:         s->mv_type                     = MV_TYPE_16X16;
yading@10:         s->current_picture.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
yading@10:         s->mv[0][0][0]                 = 0;
yading@10:         s->mv[0][0][1]                 = 0;
yading@10:         s->mb_skipped                  = 1;
yading@10:         h->mtype                      &= ~MB_TYPE_H261_FIL;
yading@10: 
yading@10:         ff_MPV_decode_mb(s, s->block);
yading@10:     }
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static const int mvmap[17] = {
yading@10:     0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16
yading@10: };
yading@10: 
yading@10: static int decode_mv_component(GetBitContext *gb, int v)
yading@10: {
yading@10:     int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
yading@10: 
yading@10:     /* check if mv_diff is valid */
yading@10:     if (mv_diff < 0)
yading@10:         return v;
yading@10: 
yading@10:     mv_diff = mvmap[mv_diff];
yading@10: 
yading@10:     if (mv_diff && !get_bits1(gb))
yading@10:         mv_diff = -mv_diff;
yading@10: 
yading@10:     v += mv_diff;
yading@10:     if (v <= -16)
yading@10:         v += 32;
yading@10:     else if (v >= 16)
yading@10:         v -= 32;
yading@10: 
yading@10:     return v;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Decode a macroblock.
yading@10:  * @return <0 if an error occurred
yading@10:  */
yading@10: static int h261_decode_block(H261Context *h, int16_t *block, int n, int coded)
yading@10: {
yading@10:     MpegEncContext *const s = &h->s;
yading@10:     int code, level, i, j, run;
yading@10:     RLTable *rl = &ff_h261_rl_tcoeff;
yading@10:     const uint8_t *scan_table;
yading@10: 
yading@10:     /* For the variable length encoding there are two code tables, one being
yading@10:      * used for the first transmitted LEVEL in INTER, INTER + MC and
yading@10:      * INTER + MC + FIL blocks, the second for all other LEVELs except the
yading@10:      * first one in INTRA blocks which is fixed length coded with 8 bits.
yading@10:      * NOTE: The two code tables only differ in one VLC so we handle that
yading@10:      * manually. */
yading@10:     scan_table = s->intra_scantable.permutated;
yading@10:     if (s->mb_intra) {
yading@10:         /* DC coef */
yading@10:         level = get_bits(&s->gb, 8);
yading@10:         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
yading@10:         if ((level & 0x7F) == 0) {
yading@10:             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n",
yading@10:                    level, s->mb_x, s->mb_y);
yading@10:             return -1;
yading@10:         }
yading@10:         /* The code 1000 0000 is not used, the reconstruction level of 1024
yading@10:          * being coded as 1111 1111. */
yading@10:         if (level == 255)
yading@10:             level = 128;
yading@10:         block[0] = level;
yading@10:         i        = 1;
yading@10:     } else if (coded) {
yading@10:         // Run  Level   Code
yading@10:         // EOB          Not possible for first level when cbp is available (that's why the table is different)
yading@10:         // 0    1       1s
yading@10:         // *    *       0*
yading@10:         int check = show_bits(&s->gb, 2);
yading@10:         i = 0;
yading@10:         if (check & 0x2) {
yading@10:             skip_bits(&s->gb, 2);
yading@10:             block[0] = (check & 0x1) ? -1 : 1;
yading@10:             i        = 1;
yading@10:         }
yading@10:     } else {
yading@10:         i = 0;
yading@10:     }
yading@10:     if (!coded) {
yading@10:         s->block_last_index[n] = i - 1;
yading@10:         return 0;
yading@10:     }
yading@10:     for (;;) {
yading@10:         code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
yading@10:         if (code < 0) {
yading@10:             av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",
yading@10:                    s->mb_x, s->mb_y);
yading@10:             return -1;
yading@10:         }
yading@10:         if (code == rl->n) {
yading@10:             /* escape */
yading@10:             /* The remaining combinations of (run, level) are encoded with a
yading@10:              * 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits
yading@10:              * level. */
yading@10:             run   = get_bits(&s->gb, 6);
yading@10:             level = get_sbits(&s->gb, 8);
yading@10:         } else if (code == 0) {
yading@10:             break;
yading@10:         } else {
yading@10:             run   = rl->table_run[code];
yading@10:             level = rl->table_level[code];
yading@10:             if (get_bits1(&s->gb))
yading@10:                 level = -level;
yading@10:         }
yading@10:         i += run;
yading@10:         if (i >= 64) {
yading@10:             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",
yading@10:                    s->mb_x, s->mb_y);
yading@10:             return -1;
yading@10:         }
yading@10:         j        = scan_table[i];
yading@10:         block[j] = level;
yading@10:         i++;
yading@10:     }
yading@10:     s->block_last_index[n] = i - 1;
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static int h261_decode_mb(H261Context *h)
yading@10: {
yading@10:     MpegEncContext *const s = &h->s;
yading@10:     int i, cbp, xy;
yading@10: 
yading@10:     cbp = 63;
yading@10:     // Read mba
yading@10:     do {
yading@10:         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,
yading@10:                                H261_MBA_VLC_BITS, 2);
yading@10: 
yading@10:         /* Check for slice end */
yading@10:         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
yading@10:         if (h->mba_diff == MBA_STARTCODE) { // start code
yading@10:             h->gob_start_code_skipped = 1;
yading@10:             return SLICE_END;
yading@10:         }
yading@10:     } while (h->mba_diff == MBA_STUFFING); // stuffing
yading@10: 
yading@10:     if (h->mba_diff < 0) {
yading@10:         if (get_bits_left(&s->gb) <= 7)
yading@10:             return SLICE_END;
yading@10: 
yading@10:         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
yading@10:         return SLICE_ERROR;
yading@10:     }
yading@10: 
yading@10:     h->mba_diff    += 1;
yading@10:     h->current_mba += h->mba_diff;
yading@10: 
yading@10:     if (h->current_mba > MBA_STUFFING)
yading@10:         return SLICE_ERROR;
yading@10: 
yading@10:     s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);
yading@10:     s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);
yading@10:     xy      = s->mb_x + s->mb_y * s->mb_stride;
yading@10:     ff_init_block_index(s);
yading@10:     ff_update_block_index(s);
yading@10: 
yading@10:     // Read mtype
yading@10:     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
yading@10:     if (h->mtype < 0) {
yading@10:         av_log(s->avctx, AV_LOG_ERROR, "illegal mtype %d\n", h->mtype);
yading@10:         return SLICE_ERROR;
yading@10:     }
yading@10:     h->mtype = ff_h261_mtype_map[h->mtype];
yading@10: 
yading@10:     // Read mquant
yading@10:     if (IS_QUANT(h->mtype))
yading@10:         ff_set_qscale(s, get_bits(&s->gb, 5));
yading@10: 
yading@10:     s->mb_intra = IS_INTRA4x4(h->mtype);
yading@10: 
yading@10:     // Read mv
yading@10:     if (IS_16X16(h->mtype)) {
yading@10:         /* Motion vector data is included for all MC macroblocks. MVD is
yading@10:          * obtained from the macroblock vector by subtracting the vector
yading@10:          * of the preceding macroblock. For this calculation the vector
yading@10:          * of the preceding macroblock is regarded as zero in the
yading@10:          * following three situations:
yading@10:          * 1) evaluating MVD for macroblocks 1, 12 and 23;
yading@10:          * 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
yading@10:          * 3) MTYPE of the previous macroblock was not MC. */
yading@10:         if ((h->current_mba ==  1) || (h->current_mba == 12) ||
yading@10:             (h->current_mba == 23) || (h->mba_diff != 1)) {
yading@10:             h->current_mv_x = 0;
yading@10:             h->current_mv_y = 0;
yading@10:         }
yading@10: 
yading@10:         h->current_mv_x = decode_mv_component(&s->gb, h->current_mv_x);
yading@10:         h->current_mv_y = decode_mv_component(&s->gb, h->current_mv_y);
yading@10:     } else {
yading@10:         h->current_mv_x = 0;
yading@10:         h->current_mv_y = 0;
yading@10:     }
yading@10: 
yading@10:     // Read cbp
yading@10:     if (HAS_CBP(h->mtype))
yading@10:         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
yading@10: 
yading@10:     if (s->mb_intra) {
yading@10:         s->current_picture.mb_type[xy] = MB_TYPE_INTRA;
yading@10:         goto intra;
yading@10:     }
yading@10: 
yading@10:     //set motion vectors
yading@10:     s->mv_dir                      = MV_DIR_FORWARD;
yading@10:     s->mv_type                     = MV_TYPE_16X16;
yading@10:     s->current_picture.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;
yading@10:     s->mv[0][0][0]                 = h->current_mv_x * 2; // gets divided by 2 in motion compensation
yading@10:     s->mv[0][0][1]                 = h->current_mv_y * 2;
yading@10: 
yading@10: intra:
yading@10:     /* decode each block */
yading@10:     if (s->mb_intra || HAS_CBP(h->mtype)) {
yading@10:         s->dsp.clear_blocks(s->block[0]);
yading@10:         for (i = 0; i < 6; i++) {
yading@10:             if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)
yading@10:                 return SLICE_ERROR;
yading@10:             cbp += cbp;
yading@10:         }
yading@10:     } else {
yading@10:         for (i = 0; i < 6; i++)
yading@10:             s->block_last_index[i] = -1;
yading@10:     }
yading@10: 
yading@10:     ff_MPV_decode_mb(s, s->block);
yading@10: 
yading@10:     return SLICE_OK;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Decode the H.261 picture header.
yading@10:  * @return <0 if no startcode found
yading@10:  */
yading@10: static int h261_decode_picture_header(H261Context *h)
yading@10: {
yading@10:     MpegEncContext *const s = &h->s;
yading@10:     int format, i;
yading@10:     uint32_t startcode = 0;
yading@10: 
yading@10:     for (i = get_bits_left(&s->gb); i > 24; i -= 1) {
yading@10:         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
yading@10: 
yading@10:         if (startcode == 0x10)
yading@10:             break;
yading@10:     }
yading@10: 
yading@10:     if (startcode != 0x10) {
yading@10:         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
yading@10:         return -1;
yading@10:     }
yading@10: 
yading@10:     /* temporal reference */
yading@10:     i = get_bits(&s->gb, 5); /* picture timestamp */
yading@10:     if (i < (s->picture_number & 31))
yading@10:         i += 32;
yading@10:     s->picture_number = (s->picture_number & ~31) + i;
yading@10: 
yading@10:     s->avctx->time_base      = (AVRational) { 1001, 30000 };
yading@10:     s->current_picture.f.pts = s->picture_number;
yading@10: 
yading@10:     /* PTYPE starts here */
yading@10:     skip_bits1(&s->gb); /* split screen off */
yading@10:     skip_bits1(&s->gb); /* camera  off */
yading@10:     skip_bits1(&s->gb); /* freeze picture release off */
yading@10: 
yading@10:     format = get_bits1(&s->gb);
yading@10: 
yading@10:     // only 2 formats possible
yading@10:     if (format == 0) { // QCIF
yading@10:         s->width     = 176;
yading@10:         s->height    = 144;
yading@10:         s->mb_width  = 11;
yading@10:         s->mb_height = 9;
yading@10:     } else { // CIF
yading@10:         s->width     = 352;
yading@10:         s->height    = 288;
yading@10:         s->mb_width  = 22;
yading@10:         s->mb_height = 18;
yading@10:     }
yading@10: 
yading@10:     s->mb_num = s->mb_width * s->mb_height;
yading@10: 
yading@10:     skip_bits1(&s->gb); /* still image mode off */
yading@10:     skip_bits1(&s->gb); /* Reserved */
yading@10: 
yading@10:     /* PEI */
yading@10:     while (get_bits1(&s->gb) != 0)
yading@10:         skip_bits(&s->gb, 8);
yading@10: 
yading@10:     /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
yading@10:      * frame, the codec crashes if it does not contain all I-blocks
yading@10:      * (e.g. when a packet is lost). */
yading@10:     s->pict_type = AV_PICTURE_TYPE_P;
yading@10: 
yading@10:     h->gob_number = 0;
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static int h261_decode_gob(H261Context *h)
yading@10: {
yading@10:     MpegEncContext *const s = &h->s;
yading@10: 
yading@10:     ff_set_qscale(s, s->qscale);
yading@10: 
yading@10:     /* decode mb's */
yading@10:     while (h->current_mba <= MBA_STUFFING) {
yading@10:         int ret;
yading@10:         /* DCT & quantize */
yading@10:         ret = h261_decode_mb(h);
yading@10:         if (ret < 0) {
yading@10:             if (ret == SLICE_END) {
yading@10:                 h261_decode_mb_skipped(h, h->current_mba, 33);
yading@10:                 return 0;
yading@10:             }
yading@10:             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",
yading@10:                    s->mb_x + s->mb_y * s->mb_stride);
yading@10:             return -1;
yading@10:         }
yading@10: 
yading@10:         h261_decode_mb_skipped(h,
yading@10:                                h->current_mba - h->mba_diff,
yading@10:                                h->current_mba - 1);
yading@10:     }
yading@10: 
yading@10:     return -1;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * returns the number of bytes consumed for building the current frame
yading@10:  */
yading@10: static int get_consumed_bytes(MpegEncContext *s, int buf_size)
yading@10: {
yading@10:     int pos = get_bits_count(&s->gb) >> 3;
yading@10:     if (pos == 0)
yading@10:         pos = 1;      // avoid infinite loops (i doubt that is needed but ...)
yading@10:     if (pos + 10 > buf_size)
yading@10:         pos = buf_size;               // oops ;)
yading@10: 
yading@10:     return pos;
yading@10: }
yading@10: 
yading@10: static int h261_decode_frame(AVCodecContext *avctx, void *data,
yading@10:                              int *got_frame, AVPacket *avpkt)
yading@10: {
yading@10:     const uint8_t *buf = avpkt->data;
yading@10:     int buf_size       = avpkt->size;
yading@10:     H261Context *h     = avctx->priv_data;
yading@10:     MpegEncContext *s  = &h->s;
yading@10:     int ret;
yading@10:     AVFrame *pict = data;
yading@10: 
yading@10:     av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
yading@10:     av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
yading@10:     s->flags  = avctx->flags;
yading@10:     s->flags2 = avctx->flags2;
yading@10: 
yading@10:     h->gob_start_code_skipped = 0;
yading@10: 
yading@10: retry:
yading@10:     init_get_bits(&s->gb, buf, buf_size * 8);
yading@10: 
yading@10:     if (!s->context_initialized)
yading@10:         // we need the IDCT permutaton for reading a custom matrix
yading@10:         if (ff_MPV_common_init(s) < 0)
yading@10:             return -1;
yading@10: 
yading@10:     /* We need to set current_picture_ptr before reading the header,
yading@10:      * otherwise we cannot store anything in there. */
yading@10:     if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {
yading@10:         int i = ff_find_unused_picture(s, 0);
yading@10:         if (i < 0)
yading@10:             return i;
yading@10:         s->current_picture_ptr = &s->picture[i];
yading@10:     }
yading@10: 
yading@10:     ret = h261_decode_picture_header(h);
yading@10: 
yading@10:     /* skip if the header was thrashed */
yading@10:     if (ret < 0) {
yading@10:         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
yading@10:         return -1;
yading@10:     }
yading@10: 
yading@10:     if (s->width != avctx->coded_width || s->height != avctx->coded_height) {
yading@10:         ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat
yading@10:         s->parse_context.buffer = 0;
yading@10:         ff_MPV_common_end(s);
yading@10:         s->parse_context = pc;
yading@10:     }
yading@10:     if (!s->context_initialized) {
yading@10:         avcodec_set_dimensions(avctx, s->width, s->height);
yading@10: 
yading@10:         goto retry;
yading@10:     }
yading@10: 
yading@10:     // for skipping the frame
yading@10:     s->current_picture.f.pict_type = s->pict_type;
yading@10:     s->current_picture.f.key_frame = s->pict_type == AV_PICTURE_TYPE_I;
yading@10: 
yading@10:     if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||
yading@10:         (avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type != AV_PICTURE_TYPE_I) ||
yading@10:          avctx->skip_frame >= AVDISCARD_ALL)
yading@10:         return get_consumed_bytes(s, buf_size);
yading@10: 
yading@10:     if (ff_MPV_frame_start(s, avctx) < 0)
yading@10:         return -1;
yading@10: 
yading@10:     ff_mpeg_er_frame_start(s);
yading@10: 
yading@10:     /* decode each macroblock */
yading@10:     s->mb_x = 0;
yading@10:     s->mb_y = 0;
yading@10: 
yading@10:     while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {
yading@10:         if (ff_h261_resync(h) < 0)
yading@10:             break;
yading@10:         h261_decode_gob(h);
yading@10:     }
yading@10:     ff_MPV_frame_end(s);
yading@10: 
yading@10:     av_assert0(s->current_picture.f.pict_type == s->current_picture_ptr->f.pict_type);
yading@10:     av_assert0(s->current_picture.f.pict_type == s->pict_type);
yading@10: 
yading@10:     if ((ret = av_frame_ref(pict, &s->current_picture_ptr->f)) < 0)
yading@10:         return ret;
yading@10:     ff_print_debug_info(s, s->current_picture_ptr, pict);
yading@10: 
yading@10:     *got_frame = 1;
yading@10: 
yading@10:     return get_consumed_bytes(s, buf_size);
yading@10: }
yading@10: 
yading@10: static av_cold int h261_decode_end(AVCodecContext *avctx)
yading@10: {
yading@10:     H261Context *h    = avctx->priv_data;
yading@10:     MpegEncContext *s = &h->s;
yading@10: 
yading@10:     ff_MPV_common_end(s);
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: AVCodec ff_h261_decoder = {
yading@10:     .name           = "h261",
yading@10:     .type           = AVMEDIA_TYPE_VIDEO,
yading@10:     .id             = AV_CODEC_ID_H261,
yading@10:     .priv_data_size = sizeof(H261Context),
yading@10:     .init           = h261_decode_init,
yading@10:     .close          = h261_decode_end,
yading@10:     .decode         = h261_decode_frame,
yading@10:     .capabilities   = CODEC_CAP_DR1,
yading@10:     .max_lowres     = 3,
yading@10:     .long_name      = NULL_IF_CONFIG_SMALL("H.261"),
yading@10: };