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FFmpeg/libavcodec/h261dec.c
Andreas Rheinhardt a247ac640d avcodec: Constify AVCodecs 
Given that the AVCodec.next pointer has now been removed, most of the
AVCodecs are not modified at all any more and can therefore be made
const (as this patch does); the only exceptions are the very few codecs
for external libraries that have a init_static_data callback.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>
2021-04-27 10:43:15 -03:00

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/*
* H.261 decoder
* Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
* 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 "libavutil/thread.h"
#include "avcodec.h"
#include "mpeg_er.h"
#include "mpegutils.h"
#include "mpegvideo.h"
#include "h263.h"
#include "h261.h"
#include "internal.h"
#define H261_MBA_VLC_BITS 8
#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_static(void)
{
INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
ff_h261_mba_bits, 1, 1,
ff_h261_mba_code, 1, 1, 540);
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_FIRST_VLC_RL(ff_h261_rl_tcoeff, 552);
}
static av_cold int h261_decode_init(AVCodecContext *avctx)
{
static AVOnce init_static_once = AV_ONCE_INIT;
H261Context *h = avctx->priv_data;
MpegEncContext *const s = &h->s;
// set defaults
ff_mpv_decode_init(s, avctx);
s->out_format = FMT_H261;
s->low_delay = 1;
avctx->pix_fmt = AV_PIX_FMT_YUV420P;
h->gob_start_code_skipped = 0;
ff_mpv_idct_init(s);
ff_thread_once(&init_static_once, h261_decode_init_static);
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 */
if (skip_1stop_8data_bits(&s->gb) < 0)
return AVERROR_INVALIDDATA;
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;
if (s->current_picture.motion_val[0]) {
int b_stride = 2*s->mb_width + 1;
int b_xy = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
}
ff_mpv_reconstruct_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 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;
}
{
OPEN_READER(re, &s->gb);
i--; // offset by -1 to allow direct indexing of scan_table
for (;;) {
UPDATE_CACHE(re, &s->gb);
GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TCOEFF_VLC_BITS, 2, 0);
if (run == 66) {
if (level) {
CLOSE_READER(re, &s->gb);
av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",
s->mb_x, s->mb_y);
return -1;
}
/* 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 = SHOW_UBITS(re, &s->gb, 6) + 1;
SKIP_CACHE(re, &s->gb, 6);
level = SHOW_SBITS(re, &s->gb, 8);
SKIP_COUNTER(re, &s->gb, 6 + 8);
} else if (level == 0) {
break;
} else {
if (SHOW_UBITS(re, &s->gb, 1))
level = -level;
SKIP_COUNTER(re, &s->gb, 1);
}
i += run;
if (i >= 64) {
CLOSE_READER(re, &s->gb);
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;
}
CLOSE_READER(re, &s->gb);
}
s->block_last_index[n] = i;
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, 1) + 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;
if (s->current_picture.motion_val[0]) {
int b_stride = 2*s->mb_width + 1;
int b_xy = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
}
intra:
/* decode each block */
if (s->mb_intra || HAS_CBP(h->mtype)) {
s->bdsp.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_reconstruct_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->framerate = (AVRational) { 30000, 1001 };
/* 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 */
if (skip_1stop_8data_bits(&s->gb) < 0)
return AVERROR_INVALIDDATA;
/* 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;
ff_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
ff_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
h->gob_start_code_skipped = 0;
retry:
init_get_bits(&s->gb, buf, buf_size * 8);
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) {
ff_mpv_common_end(s);
}
if (!s->context_initialized) {
if ((ret = ff_mpv_common_init(s)) < 0)
return ret;
ret = ff_set_dimensions(avctx, s->width, s->height);
if (ret < 0)
return ret;
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;
}
const 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 = AV_CODEC_CAP_DR1,
.caps_internal = FF_CODEC_CAP_INIT_THREADSAFE,
.max_lowres = 3,
};
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