h261 decoder by (Maarten Daniels <maarten.daniels at student dot luc dot ac dot be>)

Originally committed as revision 3176 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 875 insertions, 0 deletions

diff --git a/libavcodec/h261.c b/libavcodec/h261.c
new file mode 100644
index 0000000000..236fd8a3ca
--- /dev/null
+++ b/libavcodec/h261.c
@@ -0,0 +1,875 @@
+/*
+ * H261 decoder
+ * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
+ * Copyright (c) 2004 Maarten Daniels
+ *
+ * This library 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 of the License, or (at your option) any later version.
+ *
+ * This library 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 this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+/**
+ * @file h261.c
+ * h261codec.
+ */
+
+#include "common.h"
+#include "dsputil.h"
+#include "avcodec.h"
+#include "mpegvideo.h"
+#include "h261data.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 MAX_MBA 33
+#define IS_FIL(a)    ((a)&MB_TYPE_H261_FIL)
+
+/**
+ * H261Context
+ */
+typedef struct H261Context{
+    MpegEncContext s;
+
+    int current_mba;
+    int mba_diff;
+    int mtype;
+    int current_mv_x;
+    int current_mv_y;
+    int gob_number;
+    int loop_filter;
+    int bits_left; //8 - nr of bits left of the following frame in the last byte in this frame
+    int last_bits; //bits left of the following frame in the last byte in this frame
+}H261Context;
+
+void ff_h261_loop_filter(H261Context * h){
+    MpegEncContext * const s = &h->s;
+    int i;
+    const int linesize  = s->linesize;
+    const int uvlinesize= s->uvlinesize;
+    uint8_t *dest_y = s->dest[0];
+    uint8_t *dest_cb= s->dest[1];
+    uint8_t *dest_cr= s->dest[2];
+    uint8_t *src;
+
+    CHECKED_ALLOCZ((src),sizeof(uint8_t) * 64 );
+
+    for(i=0; i<8;i++)
+        memcpy(src+i*8,dest_y+i*linesize,sizeof(uint8_t) * 8 );
+    s->dsp.h261_v_loop_filter(dest_y, src, linesize);
+    s->dsp.h261_h_loop_filter(dest_y, src, linesize);
+
+    for(i=0; i<8;i++)
+        memcpy(src+i*8,dest_y+i*linesize + 8,sizeof(uint8_t) * 8 );
+    s->dsp.h261_v_loop_filter(dest_y + 8, src, linesize);
+    s->dsp.h261_h_loop_filter(dest_y + 8, src, linesize);
+
+    for(i=0; i<8;i++)
+        memcpy(src+i*8,dest_y+(i+8)*linesize,sizeof(uint8_t) * 8 );
+    s->dsp.h261_v_loop_filter(dest_y + 8 * linesize, src, linesize);
+    s->dsp.h261_h_loop_filter(dest_y + 8 * linesize, src, linesize);
+
+    for(i=0; i<8;i++)
+        memcpy(src+i*8,dest_y+(i+8)*linesize + 8,sizeof(uint8_t) * 8 );
+    s->dsp.h261_v_loop_filter(dest_y + 8 * linesize + 8, src, linesize);
+    s->dsp.h261_h_loop_filter(dest_y + 8 * linesize + 8, src, linesize);
+
+    for(i=0; i<8;i++)
+        memcpy(src+i*8,dest_cb+i*uvlinesize,sizeof(uint8_t) * 8 );
+    s->dsp.h261_v_loop_filter(dest_cb, src, uvlinesize);
+    s->dsp.h261_h_loop_filter(dest_cb, src, uvlinesize);
+
+    for(i=0; i<8;i++)
+        memcpy(src+i*8,dest_cr+i*uvlinesize,sizeof(uint8_t) * 8 );
+    s->dsp.h261_v_loop_filter(dest_cr, src, uvlinesize);
+    s->dsp.h261_h_loop_filter(dest_cr, src, uvlinesize);
+
+fail:
+    av_free(src);
+
+    return;
+}
+
+static int h261_decode_block(H261Context *h, DCTELEM *block,
+                             int n, int coded);
+static int h261_decode_mb(H261Context *h,
+                      DCTELEM block[6][64]);
+void ff_set_qscale(MpegEncContext * s, int qscale);
+
+/***********************************************/
+/* decoding */
+
+static VLC h261_mba_vlc;
+static VLC h261_mtype_vlc;
+static VLC h261_mv_vlc;
+static VLC h261_cbp_vlc;
+
+void init_vlc_rl(RLTable *rl);
+
+static void h261_decode_init_vlc(H261Context *h){
+    static int done = 0;
+
+    if(!done){
+        done = 1;
+        init_vlc(&h261_mba_vlc, H261_MBA_VLC_BITS, 34,
+                 h261_mba_bits, 1, 1,
+                 h261_mba_code, 1, 1);
+        init_vlc(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
+                 h261_mtype_bits, 1, 1,
+                 h261_mtype_code, 1, 1);
+        init_vlc(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
+                 &h261_mv_tab[0][1], 2, 1,
+                 &h261_mv_tab[0][0], 2, 1);
+        init_vlc(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
+                 &h261_cbp_tab[0][1], 2, 1,
+                 &h261_cbp_tab[0][0], 2, 1);
+        init_rl(&h261_rl_tcoeff);
+        init_vlc_rl(&h261_rl_tcoeff);
+    }
+}
+
+static int h261_decode_init(AVCodecContext *avctx){
+    H261Context *h= avctx->priv_data;
+    MpegEncContext * const s = &h->s;
+
+    // set defaults
+    MPV_decode_defaults(s);
+    s->avctx = avctx;
+
+    s->width = s->avctx->width;
+    s->height = s->avctx->height;
+    s->codec_id = s->avctx->codec->id;
+
+    s->out_format = FMT_H261;
+    s->low_delay= 1;
+    avctx->pix_fmt= PIX_FMT_YUV420P;
+
+    s->codec_id= avctx->codec->id;
+
+    h261_decode_init_vlc(h);
+
+    h->bits_left = 0;
+    h->last_bits = 0;
+    
+    return 0;
+}
+
+/**
+ * decodes the group of blocks header or slice header.
+ * @return <0 if an error occured
+ */
+static int h261_decode_gob_header(H261Context *h){
+    unsigned int val;
+    MpegEncContext * const s = &h->s;
+    
+    /* 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_number = get_bits(&s->gb, 4); /* GN */
+    s->qscale = get_bits(&s->gb, 5); /* GQUANT */
+
+    /* GEI */
+    while (get_bits1(&s->gb) != 0) {
+        skip_bits(&s->gb, 8);
+    }
+
+    if(s->qscale==0)
+        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;
+}
+
+/**
+ * decodes the group of blocks / video packet header.
+ * @return <0 if no resync found
+ */
+static int ff_h261_resync(H261Context *h){
+    MpegEncContext * const s = &h->s;
+    int left, ret;
+
+    if(show_bits(&s->gb, 15)==0){
+        ret= h261_decode_gob_header(h);
+        if(ret>=0)
+            return 0;
+    }
+    //ok, its not where its supposed to be ...
+    s->gb= s->last_resync_gb;
+    align_get_bits(&s->gb);
+    left= s->gb.size_in_bits - get_bits_count(&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;
+}
+
+/**
+ * decodes a skipped macroblock, called when when mba_diff > 1.
+ * @return 0
+ */
+static int h261_decode_mb_skipped(H261Context *h,
+                                  DCTELEM block[6][64])
+{
+    MpegEncContext * const s = &h->s;
+    int i;
+    const int xy = s->mb_x + s->mb_y * s->mb_stride;
+    s->mb_intra = 0;
+    for(i=0;i<6;i++)
+        s->block_last_index[i] = -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_skiped = 1;
+    return 0;
+}
+
+static int h261_decode_mb(H261Context *h,
+                          DCTELEM block[6][64])
+{
+    MpegEncContext * const s = &h->s;
+    int i, cbp, mv_x_diff, mv_y_diff, sign, xy;
+
+    cbp = 63;
+    // Read mba
+    do{
+        h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2)+1;
+    }
+    while( h->mba_diff == MAX_MBA + 1 ); // stuffing
+
+    if ( h->mba_diff < 0 )
+        return -1;
+
+    h->current_mba += h->mba_diff;
+
+    if ( h->current_mba > MAX_MBA )
+        return -1;
+    
+    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
+    int old_mtype = h->mtype;
+    h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
+    h->mtype = h261_mtype_map[h->mtype];
+
+    if (IS_FIL (h->mtype))
+        h->loop_filter = 1;
+
+    // Read mquant
+    if ( IS_QUANT ( h->mtype ) ){
+        s->qscale = 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) || ( !IS_16X16 ( old_mtype ) ))
+        {
+            h->current_mv_x = 0;
+            h->current_mv_y = 0;
+        }
+
+        mv_x_diff = get_vlc2(&s->gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
+        mv_x_diff = mvmap[mv_x_diff];
+
+        if(mv_x_diff != 0){
+            sign = get_bits1(&s->gb);
+
+            if(!sign)
+                mv_x_diff= -mv_x_diff;
+        }
+
+        mv_y_diff = get_vlc2(&s->gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
+        mv_y_diff = mvmap[mv_y_diff];
+
+        if(mv_y_diff != 0){
+            sign = get_bits1(&s->gb);
+
+            if(!sign)
+                mv_y_diff= -mv_y_diff;
+        }
+
+        //mv's are in the range -15...15
+        if((h->current_mv_x + mv_x_diff > -16) && (h->current_mv_x + mv_x_diff < 16) )
+            h->current_mv_x += mv_x_diff;
+        else
+            h->current_mv_x += (mv_x_diff + (mv_x_diff > 0 ? -32 : 32));
+
+        if((h->current_mv_y + mv_y_diff > -16) && (h->current_mv_y + mv_y_diff < 16) )
+            h->current_mv_y += mv_y_diff;
+        else
+            h->current_mv_y += (mv_y_diff + (mv_y_diff>0 ? -32 : 32));
+    }
+
+    // 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;
+    if(IS_16X16 ( h->mtype )){
+        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;
+    }
+    else{
+        h->current_mv_x = s->mv[0][0][0] = 0;
+        h->current_mv_x = s->mv[0][0][1] = 0;
+    }
+
+intra:
+    /* decode each block */
+    if(s->mb_intra || HAS_CBP(h->mtype)){
+        for (i = 0; i < 6; i++) {
+            if (h261_decode_block(h, block[i], i, cbp&32) < 0){
+                return -1;
+            }
+            cbp+=cbp;
+        }
+    }
+
+    /* per-MB end of slice check */
+    {
+        int v= show_bits(&s->gb, 15);
+
+        if(get_bits_count(&s->gb) + 15 > s->gb.size_in_bits){
+            v>>= get_bits_count(&s->gb) + 15 - s->gb.size_in_bits;
+        }
+
+        if(v==0){
+            return SLICE_END;
+        }
+    }
+    return SLICE_OK;
+}
+
+/**
+ * decodes a macroblock
+ * @return <0 if an error occured
+ */
+static int h261_decode_block(H261Context * h, DCTELEM * block,
+                             int n, int coded)
+{
+    MpegEncContext * const s = &h->s;
+    int code, level, i, j, run;
+    RLTable *rl = &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 = (int8_t)get_bits(&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;
+    return 0;
+}
+
+/**
+ * decodes the H261 picture header.
+ * @return <0 if no startcode found
+ */
+int h261_decode_picture_header(H261Context *h){
+    MpegEncContext * const s = &h->s;
+    int format, i;
+    static int h261_framecounter = 0;
+    uint32_t startcode;
+    align_get_bits(&s->gb);
+
+    startcode = (h->last_bits << (12 - (8-h->bits_left))) | get_bits(&s->gb, 20-8 - (8- h->bits_left));
+
+    for(i= s->gb.size_in_bits - get_bits_count(&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 */
+    s->picture_number = get_bits(&s->gb, 5); /* picture timestamp */
+
+    /* 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);
+    }
+
+    //h261 has no I-FRAMES, pass the test in MPV_frame_start in mpegvideo.c
+    if(h261_framecounter > 1)
+        s->pict_type = P_TYPE;
+    else
+        s->pict_type = I_TYPE;
+
+    h261_framecounter++;
+
+    h->gob_number = 0;
+    return 0;
+}
+
+static int h261_decode_gob(H261Context *h){
+    MpegEncContext * const s = &h->s;
+    int i;
+    
+    ff_set_qscale(s, s->qscale);
+    while(h->current_mba <= MAX_MBA)
+    {
+        int ret;
+        /* DCT & quantize */
+        s->dsp.clear_blocks(s->block[0]);
+        ret= h261_decode_mb(h, s->block);
+        if(ret<0){
+            const int xy= s->mb_x + s->mb_y*s->mb_stride;
+            if(ret==SLICE_END){
+                MPV_decode_mb(s, s->block);
+                if(h->loop_filter){
+                    ff_h261_loop_filter(h);
+                }
+                h->loop_filter = 0;
+                for(i=1; i<h->mba_diff; i++){
+                    s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1-i) % 11);
+                    s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1-i) / 11);
+                    ff_init_block_index(s);
+                    ff_update_block_index(s);
+                    s->dsp.clear_blocks(s->block[0]);
+                    ret= h261_decode_mb_skipped(h, s->block);
+                    MPV_decode_mb(s, s->block);
+                }
+                
+                return 0;
+            }else if(ret==SLICE_NOEND){
+                av_log(s->avctx, AV_LOG_ERROR, "Slice mismatch at MB: %d\n", xy);
+                return -1;
+            }
+            av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", xy);
+            return -1;
+        }
+        MPV_decode_mb(s, s->block);
+        if(h->loop_filter){
+            ff_h261_loop_filter(h);
+        }
+
+        h->loop_filter = 0;
+        for(i=1; i<h->mba_diff; i++){
+            s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1-i) % 11);
+            s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1-i) / 11);
+            ff_init_block_index(s);
+            ff_update_block_index(s);
+            s->dsp.clear_blocks(s->block[0]);
+            ret= h261_decode_mb_skipped(h, s->block);
+            MPV_decode_mb(s, s->block);
+        }
+    }
+    
+    return -1;
+}
+
+static int h261_find_frame_end(ParseContext *pc, AVCodecContext* avctx, const uint8_t *buf, int buf_size){
+    int vop_found, i, j, bits_left, last_bits;
+    uint32_t state;
+
+    H261Context *h = avctx->priv_data;
+
+    if(h){
+        bits_left = h->bits_left;
+        last_bits = h->last_bits;
+    }
+    else{
+        bits_left = 0;
+        last_bits = 0;
+    }
+
+    vop_found= pc->frame_start_found;
+    state= pc->state;
+    if(bits_left!=0 && !vop_found)
+        state = state << (8-bits_left) | last_bits;
+    i=0;
+    if(!vop_found){
+        for(i=0; i<buf_size; i++){
+            state= (state<<8) | buf[i];
+            for(j=0; j<8; j++){
+                if(( (  (state<<j)  |  (buf[i]>>(8-j))  )>>(32-20) == 0x10 )&&(((state >> (17-j)) & 0x4000) == 0x0)){
+                    i++;
+                    vop_found=1;
+                    break;
+                }
+            }
+            if(vop_found)
+                    break;    
+        }
+    }
+    if(vop_found){
+        for(; i<buf_size; i++){
+            if(avctx->flags & CODEC_FLAG_TRUNCATED)//XXX ffplay workaround, someone a better solution?
+                state= (state<<8) | buf[i];
+            for(j=0; j<8; j++){
+                if(( (  (state<<j)  |  (buf[i]>>(8-j))  )>>(32-20) == 0x10 )&&(((state >> (17-j)) & 0x4000) == 0x0)){
+                    pc->frame_start_found=0;
+                    pc->state=-1;
+                    return i-3;
+                }
+            }
+        }
+    }
+
+    pc->frame_start_found= vop_found;
+    pc->state= state;
+    return END_NOT_FOUND;
+}
+
+static int h261_parse(AVCodecParserContext *s,
+                      AVCodecContext *avctx,
+                      uint8_t **poutbuf, int *poutbuf_size, 
+                      const uint8_t *buf, int buf_size)
+{
+    ParseContext *pc = s->priv_data;
+    int next;
+    
+    next= h261_find_frame_end(pc,avctx, buf, buf_size);
+    if (ff_combine_frame(pc, next, (uint8_t **)&buf, &buf_size) < 0) {
+        *poutbuf = NULL;
+        *poutbuf_size = 0;
+        return buf_size;
+    }
+    *poutbuf = (uint8_t *)buf;
+    *poutbuf_size = buf_size;
+    return next;
+}
+
+/**
+ * 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)+7)>>3;
+
+    if(s->flags&CODEC_FLAG_TRUNCATED){
+        pos -= s->parse_context.last_index;
+        if(pos<0) pos=0;// padding is not really read so this might be -1
+        return pos;
+    }else{
+        if(pos==0) pos=1; //avoid infinite loops (i doubt thats needed but ...)
+        if(pos+10>buf_size) pos=buf_size; // oops ;)
+
+        return pos;
+    }
+}
+
+static int h261_decode_frame(AVCodecContext *avctx,
+                             void *data, int *data_size,
+                             uint8_t *buf, int buf_size)
+{
+    H261Context *h= avctx->priv_data;
+    MpegEncContext *s = &h->s;
+    int ret;
+    AVFrame *pict = data;
+
+#ifdef PRINT_FRAME_TIME
+uint64_t time= rdtsc();
+#endif
+#ifdef DEBUG
+    printf("*****frame %d size=%d\n", avctx->frame_number, buf_size);
+    printf("bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
+#endif
+    s->flags= avctx->flags;
+    s->flags2= avctx->flags2;
+
+    /* no supplementary picture */
+    if (buf_size == 0) {
+        /* special case for last picture */
+        if (s->low_delay==0 && s->next_picture_ptr) {
+            *pict= *(AVFrame*)s->next_picture_ptr;
+            s->next_picture_ptr= NULL;
+
+            *data_size = sizeof(AVFrame);
+        }
+
+        return 0;
+    }
+
+    if(s->flags&CODEC_FLAG_TRUNCATED){
+        int next;
+
+        next= h261_find_frame_end(&s->parse_context,avctx, buf, buf_size);
+
+        if( ff_combine_frame(&s->parse_context, next, &buf, &buf_size) < 0 )
+            return buf_size;
+    }
+
+
+retry:
+
+    if(s->bitstream_buffer_size && buf_size<20){
+        init_get_bits(&s->gb, s->bitstream_buffer, s->bitstream_buffer_size*8);
+    }else
+        init_get_bits(&s->gb, buf, buf_size*8);
+    s->bitstream_buffer_size=0;
+
+    if(!s->context_initialized){
+        if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
+            return -1;
+    }
+
+    //we need to set current_picture_ptr before reading the header, otherwise we cant store anyting im there
+    if(s->current_picture_ptr==NULL || s->current_picture_ptr->data[0]){
+        int i= ff_find_unused_picture(s, 0);
+        s->current_picture_ptr= &s->picture[i];
+    }
+
+    ret = h261_decode_picture_header(h);
+
+    if(ret==FRAME_SKIPED) return get_consumed_bytes(s, buf_size);
+
+    /* 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->width || s->height != avctx->height){
+        ParseContext pc= s->parse_context; //FIXME move these demuxng hack to avformat
+        s->parse_context.buffer=0;
+        MPV_common_end(s);
+        s->parse_context= pc;
+    }
+    if (!s->context_initialized) {
+        avctx->width = s->width;
+        avctx->height = s->height;
+
+        goto retry;
+    }
+
+    // for hurry_up==5
+    s->current_picture.pict_type= s->pict_type;
+    s->current_picture.key_frame= s->pict_type == I_TYPE;
+
+    /* skip everything if we are in a hurry>=5 */
+    if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);
+
+    if(MPV_frame_start(s, avctx) < 0)
+        return -1;
+
+    ff_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(ff_h261_resync(h)<0)
+            break;
+        h261_decode_gob(h);
+    }
+    MPV_frame_end(s);
+
+    // h261 doesn't have byte aligned codes
+    // store the bits of the next frame that are left in the last byte
+    // in the H261Context and remember the number of stored bits
+    {
+        int bitsleft;
+        int current_pos= get_bits_count(&s->gb)>>3;
+        bitsleft =  (current_pos<<3) - get_bits_count(&s->gb);
+        h->bits_left = - bitsleft;
+        if(bitsleft > 0)
+            h->last_bits= get_bits(&s->gb, 8 - h->bits_left);
+        else
+            h->last_bits = 0;
+    }
+
+assert(s->current_picture.pict_type == s->current_picture_ptr->pict_type);
+assert(s->current_picture.pict_type == s->pict_type);
+    if(s->low_delay){
+        *pict= *(AVFrame*)&s->current_picture;
+        ff_print_debug_info(s, pict);
+    }else{
+        *pict= *(AVFrame*)&s->last_picture;
+        if(pict)
+            ff_print_debug_info(s, pict);
+    }
+
+    /* Return the Picture timestamp as the frame number */
+    /* we substract 1 because it is added on utils.c    */
+    avctx->frame_number = s->picture_number - 1;
+
+    /* dont output the last pic after seeking */
+    if(s->last_picture_ptr || s->low_delay)
+        *data_size = sizeof(AVFrame);
+#ifdef PRINT_FRAME_TIME
+printf("%Ld\n", rdtsc()-time);
+#endif
+
+return get_consumed_bytes(s, buf_size);
+}
+
+static int h261_decode_end(AVCodecContext *avctx)
+{
+    H261Context *h= avctx->priv_data;
+    MpegEncContext *s = &h->s;
+
+    MPV_common_end(s);
+    return 0;
+}
+
+AVCodec h261_decoder = {
+    "h261",
+    CODEC_TYPE_VIDEO,
+    CODEC_ID_H261,
+    sizeof(H261Context),
+    h261_decode_init,
+    NULL,
+    h261_decode_end,
+    h261_decode_frame,
+    CODEC_CAP_TRUNCATED,
+};
+
+AVCodecParser h261_parser = {
+    { CODEC_ID_H261 },
+    sizeof(ParseContext),
+    NULL,
+    h261_parse,
+    ff_parse_close,
+};