static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s, uint32_t length) { uint32_t sequence_number; if (length != 26) return AVERROR_INVALIDDATA; if (!(s->state & PNG_IHDR)) { av_log(avctx, AV_LOG_ERROR, "fctl before IHDR\n"); return AVERROR_INVALIDDATA; } s->last_w = s->cur_w; s->last_h = s->cur_h; s->last_x_offset = s->x_offset; s->last_y_offset = s->y_offset; s->last_dispose_op = s->dispose_op; sequence_number = bytestream2_get_be32(&s->gb); s->cur_w = bytestream2_get_be32(&s->gb); s->cur_h = bytestream2_get_be32(&s->gb); s->x_offset = bytestream2_get_be32(&s->gb); s->y_offset = bytestream2_get_be32(&s->gb); bytestream2_skip(&s->gb, 4); /* delay_num (2), delay_den (2) */ s->dispose_op = bytestream2_get_byte(&s->gb); s->blend_op = bytestream2_get_byte(&s->gb); bytestream2_skip(&s->gb, 4); /* crc */ if (sequence_number == 0 && (s->cur_w != s->width || s->cur_h != s->height || s->x_offset != 0 || s->y_offset != 0) || s->cur_w <= 0 || s->cur_h <= 0 || s->x_offset < 0 || s->y_offset < 0 || s->cur_w > s->width - s->x_offset|| s->cur_h > s->height - s->y_offset) return AVERROR_INVALIDDATA; if (sequence_number == 0 && s->dispose_op == APNG_DISPOSE_OP_PREVIOUS) { // No previous frame to revert to for the first frame // Spec says to just treat it as a APNG_DISPOSE_OP_BACKGROUND s->dispose_op = APNG_DISPOSE_OP_BACKGROUND; } if (s->dispose_op == APNG_BLEND_OP_OVER && !s->has_trns && ( avctx->pix_fmt == AV_PIX_FMT_RGB24 || avctx->pix_fmt == AV_PIX_FMT_RGB48BE || avctx->pix_fmt == AV_PIX_FMT_PAL8 || avctx->pix_fmt == AV_PIX_FMT_GRAY8 || avctx->pix_fmt == AV_PIX_FMT_GRAY16BE || avctx->pix_fmt == AV_PIX_FMT_MONOBLACK )) { // APNG_DISPOSE_OP_OVER is the same as APNG_DISPOSE_OP_SOURCE when there is no alpha channel s->dispose_op = APNG_BLEND_OP_SOURCE; } return 0; }