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H.261 decoder improvements 

- GOB's can exist of only MBA_STUFFING codes: it crashed before, but it is fixed now
- Clearer code
- Some extra checks so the decoder is more resilient against errors
patch by (Maarten Daniels <maarten dot daniels at student dot luc dot ac dot be>)

Originally committed as revision 3457 to svn://svn.ffmpeg.org/ffmpeg/trunk
tags/v0.5
Maarten Daniels Michael Niedermayer 21 years ago
parent
d92b58073e
commit
49e5dcbce5
2 changed files with 88 additions and 92 deletions
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  1. +82
    -88
      libavcodec/h261.c
  2. +6
    -4
      libavcodec/h261data.h

+ 82
- 88
libavcodec/h261.c View File

@@ -36,7 +36,8 @@
#define H261_CBP_VLC_BITS 9
#define TCOEFF_VLC_BITS 9

#define MAX_MBA 33
#define MBA_STUFFING 33
#define MBA_STARTCODE 34
#define IS_FIL(a) ((a)&MB_TYPE_H261_FIL)

/**
@@ -51,9 +52,9 @@ typedef struct H261Context{
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
int gob_start_code_skipped; // 1 if gob start code is already read before gob header is read
}H261Context;

void ff_h261_loop_filter(H261Context * h){
@@ -74,8 +75,7 @@ void ff_h261_loop_filter(H261Context * h){

static int h261_decode_block(H261Context *h, DCTELEM *block,
int n, int coded);
static int h261_decode_mb(H261Context *h,
DCTELEM block[6][64]);
static int h261_decode_mb(H261Context *h);
void ff_set_qscale(MpegEncContext * s, int qscale);

/***********************************************/
@@ -93,7 +93,7 @@ static void h261_decode_init_vlc(H261Context *h){

if(!done){
done = 1;
init_vlc(&h261_mba_vlc, H261_MBA_VLC_BITS, 34,
init_vlc(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
h261_mba_bits, 1, 1,
h261_mba_code, 1, 1);
init_vlc(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
@@ -132,6 +132,7 @@ static int h261_decode_init(AVCodecContext *avctx){

h->bits_left = 0;
h->last_bits = 0;
h->gob_start_code_skipped = 0;
return 0;
}
@@ -144,17 +145,31 @@ 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;
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);
}

/* 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);
@@ -180,27 +195,34 @@ static int ff_h261_resync(H261Context *h){
MpegEncContext * const s = &h->s;
int left, ret;

if(show_bits(&s->gb, 15)==0){
if ( h->gob_start_code_skipped ){
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){
else{
if(show_bits(&s->gb, 15)==0){
GetBitContext bak= s->gb;

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;
s->gb= bak;
}
skip_bits(&s->gb, 8);
}
skip_bits(&s->gb, 8);
}

return -1;
@@ -245,6 +267,11 @@ static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )

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))
@@ -257,32 +284,41 @@ static int decode_mv_component(GetBitContext *gb, int v){
return v;
}

static int h261_decode_mb(H261Context *h,
DCTELEM block[6][64])
{
static int h261_decode_mb(H261Context *h){
MpegEncContext * const s = &h->s;
int i, cbp, xy, old_mtype;

cbp = 63;
// Read mba
do{
h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2)+1;
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 == MAX_MBA + 1 ); // stuffing
while( h->mba_diff == MBA_STUFFING ); // stuffing

if ( h->mba_diff < 0 )
return -1;
if ( h->mba_diff < 0 ){
if ( get_bits_count(&s->gb) + 7 >= s->gb.size_in_bits )
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 > MAX_MBA )
return -1;
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);
s->dsp.clear_blocks(s->block[0]);
@@ -292,9 +328,6 @@ static int h261_decode_mb(H261Context *h,
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 ) ){
ff_set_qscale(s, get_bits(&s->gb, 5));
@@ -348,25 +381,19 @@ 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;
if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
return SLICE_ERROR;
}
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;
}
MPV_decode_mb(s, s->block);

if(v==0){
return SLICE_END;
}
if(IS_FIL (h->mtype)){
ff_h261_loop_filter(h);
}

return SLICE_OK;
}

@@ -459,7 +486,6 @@ static int h261_decode_block(H261Context * h, DCTELEM * block,
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);

@@ -510,13 +536,9 @@ int h261_decode_picture_header(H261Context *h){
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++;
// h261 has no I-FRAMES, but if we pass I_TYPE 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 = P_TYPE;

h->gob_number = 0;
return 0;
@@ -524,52 +546,24 @@ int h261_decode_picture_header(H261Context *h){

static int h261_decode_gob(H261Context *h){
MpegEncContext * const s = &h->s;
int v;
ff_set_qscale(s, s->qscale);

/* check for empty gob */
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){
h261_decode_mb_skipped(h, 0, 33);
return 0;
}

/* decode mb's */
while(h->current_mba <= MAX_MBA)
while(h->current_mba <= MBA_STUFFING)
{
int ret;
/* DCT & quantize */
ret= h261_decode_mb(h, s->block);
ret= h261_decode_mb(h);
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;
h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
h261_decode_mb_skipped(h, h->current_mba, 33);
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);
av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
return -1;
}
MPV_decode_mb(s, s->block);
if(h->loop_filter){
ff_h261_loop_filter(h);
}

h->loop_filter = 0;
h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
}


+ 6
- 4
libavcodec/h261data.h View File

@@ -5,7 +5,7 @@
#define MB_TYPE_H261_FIL 0x800000

// H.261 VLC table for macroblock addressing
const uint8_t h261_mba_code[34] = {
const uint8_t h261_mba_code[35] = {
1, 3, 2, 3,
2, 3, 2, 7,
6, 11, 10, 9,
@@ -15,10 +15,11 @@ const uint8_t h261_mba_code[34] = {
32, 31, 30, 29,
28, 27, 26, 25,
24,
15 //(MBA stuffing)
15, //(MBA stuffing)
1 //(start code)
};

const uint8_t h261_mba_bits[34] = {
const uint8_t h261_mba_bits[35] = {
1, 3, 3, 4,
4, 5, 5, 7,
7, 8, 8, 8,
@@ -28,7 +29,8 @@ const uint8_t h261_mba_bits[34] = {
11, 11, 11, 11,
11, 11, 11, 11,
11,
11 //(MBA stuffing)
11, //(MBA stuffing)
16 //(start code)
};

//H.261 VLC table for macroblock type


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