FFmpeg/libavcodec/vc1_parser.c

/*
 * VC-1 and WMV3 parser
 * Copyright (c) 2006-2007 Konstantin Shishkov
 * Partly based on vc9.c (c) 2005 Anonymous, Alex Beregszaszi, Michael Niedermayer
 *
 * This file is part of Libav.
 *
 * Libav 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.
 *
 * Libav 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 Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * VC-1 and WMV3 parser
 */

#include "libavutil/attributes.h"
#include "parser.h"
#include "vc1.h"
#include "get_bits.h"

/** The maximum number of bytes of a sequence, entry point or
 *  frame header whose values we pay any attention to */
#define UNESCAPED_THRESHOLD 37

/** The maximum number of bytes of a sequence, entry point or
 *  frame header which must be valid memory (because they are
 *  used to update the bitstream cache in skip_bits() calls)
 */
#define UNESCAPED_LIMIT 144

typedef enum {
    NO_MATCH,
    ONE_ZERO,
    TWO_ZEROS,
    ONE
} VC1ParseSearchState;

typedef struct {
    ParseContext pc;
    VC1Context v;
    uint8_t prev_start_code;
    size_t bytes_to_skip;
    uint8_t unesc_buffer[UNESCAPED_LIMIT];
    size_t unesc_index;
    VC1ParseSearchState search_state;
} VC1ParseContext;

static void vc1_extract_header(AVCodecParserContext *s, AVCodecContext *avctx,
                               const uint8_t *buf, int buf_size)
{
    /* Parse the header we just finished unescaping */
    VC1ParseContext *vpc = s->priv_data;
    GetBitContext gb;
    vpc->v.s.avctx = avctx;
    vpc->v.parse_only = 1;
    init_get_bits(&gb, buf, buf_size * 8);
    switch (vpc->prev_start_code) {
    case VC1_CODE_SEQHDR & 0xFF:
        ff_vc1_decode_sequence_header(avctx, &vpc->v, &gb);
        break;
    case VC1_CODE_ENTRYPOINT & 0xFF:
        ff_vc1_decode_entry_point(avctx, &vpc->v, &gb);
        break;
    case VC1_CODE_FRAME & 0xFF:
        if(vpc->v.profile < PROFILE_ADVANCED)
            ff_vc1_parse_frame_header    (&vpc->v, &gb);
        else
            ff_vc1_parse_frame_header_adv(&vpc->v, &gb);

        /* keep AV_PICTURE_TYPE_BI internal to VC1 */
        if (vpc->v.s.pict_type == AV_PICTURE_TYPE_BI)
            s->pict_type = AV_PICTURE_TYPE_B;
        else
            s->pict_type = vpc->v.s.pict_type;

        if (avctx->ticks_per_frame > 1){
            // process pulldown flags
            s->repeat_pict = 1;
            // Pulldown flags are only valid when 'broadcast' has been set.
            // So ticks_per_frame will be 2
            if (vpc->v.rff){
                // repeat field
                s->repeat_pict = 2;
            }else if (vpc->v.rptfrm){
                // repeat frames
                s->repeat_pict = vpc->v.rptfrm * 2 + 1;
            }
        }else{
            s->repeat_pict = 0;
        }

        if (vpc->v.broadcast && vpc->v.interlace && !vpc->v.psf)
            s->field_order = vpc->v.tff ? AV_FIELD_TT : AV_FIELD_BB;
        else
            s->field_order = AV_FIELD_PROGRESSIVE;

        break;
    }
}

static int vc1_parse(AVCodecParserContext *s,
                           AVCodecContext *avctx,
                           const uint8_t **poutbuf, int *poutbuf_size,
                           const uint8_t *buf, int buf_size)
{
    /* Here we do the searching for frame boundaries and headers at
     * the same time. Only a minimal amount at the start of each
     * header is unescaped. */
    VC1ParseContext *vpc = s->priv_data;
    int pic_found = vpc->pc.frame_start_found;
    uint8_t *unesc_buffer = vpc->unesc_buffer;
    size_t unesc_index = vpc->unesc_index;
    VC1ParseSearchState search_state = vpc->search_state;
    int next = END_NOT_FOUND;
    int i = vpc->bytes_to_skip;

    if (pic_found && buf_size == 0) {
        /* EOF considered as end of frame */
        memset(unesc_buffer + unesc_index, 0, UNESCAPED_THRESHOLD - unesc_index);
        vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
        next = 0;
    }
    while (i < buf_size) {
        int start_code_found = 0;
        uint8_t b;
        while (i < buf_size && unesc_index < UNESCAPED_THRESHOLD) {
            b = buf[i++];
            unesc_buffer[unesc_index++] = b;
            if (search_state <= ONE_ZERO)
                search_state = b ? NO_MATCH : search_state + 1;
            else if (search_state == TWO_ZEROS) {
                if (b == 1)
                    search_state = ONE;
                else if (b > 1) {
                    if (b == 3)
                        unesc_index--; // swallow emulation prevention byte
                    search_state = NO_MATCH;
                }
            }
            else { // search_state == ONE
                // Header unescaping terminates early due to detection of next start code
                search_state = NO_MATCH;
                start_code_found = 1;
                break;
            }
        }
        if ((s->flags & PARSER_FLAG_COMPLETE_FRAMES) &&
                unesc_index >= UNESCAPED_THRESHOLD &&
                vpc->prev_start_code == (VC1_CODE_FRAME & 0xFF))
        {
            // No need to keep scanning the rest of the buffer for
            // start codes if we know it contains a complete frame and
            // we've already unescaped all we need of the frame header
            vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
            break;
        }
        if (unesc_index >= UNESCAPED_THRESHOLD && !start_code_found) {
            while (i < buf_size) {
                if (search_state == NO_MATCH) {
                    i += vpc->v.vc1dsp.startcode_find_candidate(buf + i, buf_size - i);
                    if (i < buf_size) {
                        search_state = ONE_ZERO;
                    }
                    i++;
                } else {
                    b = buf[i++];
                    if (search_state == ONE_ZERO)
                        search_state = b ? NO_MATCH : TWO_ZEROS;
                    else if (search_state == TWO_ZEROS) {
                        if (b >= 1)
                            search_state = b == 1 ? ONE : NO_MATCH;
                    }
                    else { // search_state == ONE
                        search_state = NO_MATCH;
                        start_code_found = 1;
                        break;
                    }
                }
            }
        }
        if (start_code_found) {
            vc1_extract_header(s, avctx, unesc_buffer, unesc_index);

            vpc->prev_start_code = b;
            unesc_index = 0;

            if (!(s->flags & PARSER_FLAG_COMPLETE_FRAMES)) {
                if (!pic_found && (b == (VC1_CODE_FRAME & 0xFF) || b == (VC1_CODE_FIELD & 0xFF))) {
                    pic_found = 1;
                }
                else if (pic_found && b != (VC1_CODE_FIELD & 0xFF) && b != (VC1_CODE_SLICE & 0xFF)) {
                    next = i - 4;
                    pic_found = b == (VC1_CODE_FRAME & 0xFF);
                    break;
                }
            }
        }
    }

    vpc->pc.frame_start_found = pic_found;
    vpc->unesc_index = unesc_index;
    vpc->search_state = search_state;

    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
        next = buf_size;
    } else {
        if (ff_combine_frame(&vpc->pc, next, &buf, &buf_size) < 0) {
            vpc->bytes_to_skip = 0;
            *poutbuf = NULL;
            *poutbuf_size = 0;
            return buf_size;
        }
    }

    /* If we return with a valid pointer to a combined frame buffer
     * then on the next call then we'll have been unhelpfully rewound
     * by up to 4 bytes (depending upon whether the start code
     * overlapped the input buffer, and if so by how much). We don't
     * want this: it will either cause spurious second detections of
     * the start code we've already seen, or cause extra bytes to be
     * inserted at the start of the unescaped buffer. */
    vpc->bytes_to_skip = 4;
    if (next < 0)
        vpc->bytes_to_skip += next;

    *poutbuf = buf;
    *poutbuf_size = buf_size;
    return next;
}

static int vc1_split(AVCodecContext *avctx,
                           const uint8_t *buf, int buf_size)
{
    int i;
    uint32_t state= -1;
    int charged=0;

    for(i=0; i<buf_size; i++){
        state= (state<<8) | buf[i];
        if(IS_MARKER(state)){
            if(state == VC1_CODE_SEQHDR || state == VC1_CODE_ENTRYPOINT){
                charged=1;
            }else if(charged){
                return i-3;
            }
        }
    }
    return 0;
}

static av_cold int vc1_parse_init(AVCodecParserContext *s)
{
    VC1ParseContext *vpc = s->priv_data;
    vpc->v.s.slice_context_count = 1;
    vpc->prev_start_code = 0;
    vpc->bytes_to_skip = 0;
    vpc->unesc_index = 0;
    vpc->search_state = NO_MATCH;
    return ff_vc1_init_common(&vpc->v);
}

AVCodecParser ff_vc1_parser = {
    .codec_ids      = { AV_CODEC_ID_VC1 },
    .priv_data_size = sizeof(VC1ParseContext),
    .parser_init    = vc1_parse_init,
    .parser_parse   = vc1_parse,
    .parser_close   = ff_parse_close,
    .split          = vc1_split,
};