static int decode_update_thread_context(AVCodecContext *dst,
                                        const AVCodecContext *src)
{
    H264Context *h = dst->priv_data, *h1 = src->priv_data;
    int inited = h->context_initialized, err = 0;
    int context_reinitialized = 0;
    int i, ret;

    if (dst == src || !h1->context_initialized)
        return 0;

    if (inited &&
        (h->width                 != h1->width                 ||
         h->height                != h1->height                ||
         h->mb_width              != h1->mb_width              ||
         h->mb_height             != h1->mb_height             ||
         h->sps.bit_depth_luma    != h1->sps.bit_depth_luma    ||
         h->sps.chroma_format_idc != h1->sps.chroma_format_idc ||
         h->sps.colorspace        != h1->sps.colorspace)) {

        /* set bits_per_raw_sample to the previous value. the check for changed
         * bit depth in h264_set_parameter_from_sps() uses it and sets it to
         * the current value */
        h->avctx->bits_per_raw_sample = h->sps.bit_depth_luma;

        av_freep(&h->bipred_scratchpad);

        h->width     = h1->width;
        h->height    = h1->height;
        h->mb_height = h1->mb_height;
        h->mb_width  = h1->mb_width;
        h->mb_num    = h1->mb_num;
        h->mb_stride = h1->mb_stride;
        h->b_stride  = h1->b_stride;

        if ((err = h264_slice_header_init(h, 1)) < 0) {
            av_log(h->avctx, AV_LOG_ERROR, "h264_slice_header_init() failed");
            return err;
        }
        context_reinitialized = 1;

        /* update linesize on resize. The decoder doesn't
         * necessarily call h264_frame_start in the new thread */
        h->linesize   = h1->linesize;
        h->uvlinesize = h1->uvlinesize;

        /* copy block_offset since frame_start may not be called */
        memcpy(h->block_offset, h1->block_offset, sizeof(h->block_offset));
    }

    if (!inited) {
        for (i = 0; i < MAX_SPS_COUNT; i++)
            av_freep(h->sps_buffers + i);

        for (i = 0; i < MAX_PPS_COUNT; i++)
            av_freep(h->pps_buffers + i);

        memcpy(h, h1, sizeof(*h1));
        memset(h->sps_buffers, 0, sizeof(h->sps_buffers));
        memset(h->pps_buffers, 0, sizeof(h->pps_buffers));
        memset(&h->er, 0, sizeof(h->er));
        memset(&h->me, 0, sizeof(h->me));
        memset(&h->mb, 0, sizeof(h->mb));
        memset(&h->mb_luma_dc, 0, sizeof(h->mb_luma_dc));
        memset(&h->mb_padding, 0, sizeof(h->mb_padding));
        h->context_initialized = 0;

        memset(&h->cur_pic, 0, sizeof(h->cur_pic));
        av_frame_unref(&h->cur_pic.f);
        h->cur_pic.tf.f = &h->cur_pic.f;

        h->avctx             = dst;
        h->DPB               = NULL;
        h->qscale_table_pool = NULL;
        h->mb_type_pool      = NULL;
        h->ref_index_pool    = NULL;
        h->motion_val_pool   = NULL;

        ret = ff_h264_alloc_tables(h);
        if (ret < 0) {
            av_log(dst, AV_LOG_ERROR, "Could not allocate memory for h264\n");
            return ret;
        }
        ret = context_init(h);
        if (ret < 0) {
            av_log(dst, AV_LOG_ERROR, "context_init() failed.\n");
            return ret;
        }

        for (i = 0; i < 2; i++) {
            h->rbsp_buffer[i]      = NULL;
            h->rbsp_buffer_size[i] = 0;
        }
        h->bipred_scratchpad = NULL;
        h->edge_emu_buffer   = NULL;

        h->thread_context[0] = h;

        h->context_initialized = 1;
    }

    h->avctx->coded_height  = h1->avctx->coded_height;
    h->avctx->coded_width   = h1->avctx->coded_width;
    h->avctx->width         = h1->avctx->width;
    h->avctx->height        = h1->avctx->height;
    h->coded_picture_number = h1->coded_picture_number;
    h->first_field          = h1->first_field;
    h->picture_structure    = h1->picture_structure;
    h->qscale               = h1->qscale;
    h->droppable            = h1->droppable;
    h->low_delay            = h1->low_delay;

    for (i = 0; i < MAX_PICTURE_COUNT; i++) {
        unref_picture(h, &h->DPB[i]);
        if (h1->DPB[i].f.buf[0] &&
            (ret = ref_picture(h, &h->DPB[i], &h1->DPB[i])) < 0)
            return ret;
    }

    h->cur_pic_ptr = REBASE_PICTURE(h1->cur_pic_ptr, h, h1);
    unref_picture(h, &h->cur_pic);
    if ((ret = ref_picture(h, &h->cur_pic, &h1->cur_pic)) < 0)
        return ret;

    h->workaround_bugs = h1->workaround_bugs;
    h->low_delay       = h1->low_delay;
    h->droppable       = h1->droppable;

    /* frame_start may not be called for the next thread (if it's decoding
     * a bottom field) so this has to be allocated here */
    err = alloc_scratch_buffers(h, h1->linesize);
    if (err < 0)
        return err;

    // extradata/NAL handling
    h->is_avc = h1->is_avc;

    // SPS/PPS
    if ((ret = copy_parameter_set((void **)h->sps_buffers,
                                  (void **)h1->sps_buffers,
                                  MAX_SPS_COUNT, sizeof(SPS))) < 0)
        return ret;
    h->sps = h1->sps;
    if ((ret = copy_parameter_set((void **)h->pps_buffers,
                                  (void **)h1->pps_buffers,
                                  MAX_PPS_COUNT, sizeof(PPS))) < 0)
        return ret;
    h->pps = h1->pps;

    // Dequantization matrices
    // FIXME these are big - can they be only copied when PPS changes?
    copy_fields(h, h1, dequant4_buffer, dequant4_coeff);

    for (i = 0; i < 6; i++)
        h->dequant4_coeff[i] = h->dequant4_buffer[0] +
                               (h1->dequant4_coeff[i] - h1->dequant4_buffer[0]);

    for (i = 0; i < 6; i++)
        h->dequant8_coeff[i] = h->dequant8_buffer[0] +
                               (h1->dequant8_coeff[i] - h1->dequant8_buffer[0]);

    h->dequant_coeff_pps = h1->dequant_coeff_pps;

    // POC timing
    copy_fields(h, h1, poc_lsb, redundant_pic_count);

    // reference lists
    copy_fields(h, h1, short_ref, cabac_init_idc);

    copy_picture_range(h->short_ref, h1->short_ref, 32, h, h1);
    copy_picture_range(h->long_ref, h1->long_ref, 32, h, h1);
    copy_picture_range(h->delayed_pic, h1->delayed_pic,
                       MAX_DELAYED_PIC_COUNT + 2, h, h1);

    h->last_slice_type = h1->last_slice_type;

    if (context_reinitialized)
        h264_set_parameter_from_sps(h);

    if (!h->cur_pic_ptr)
        return 0;

    if (!h->droppable) {
        err = ff_h264_execute_ref_pic_marking(h, h->mmco, h->mmco_index);
        h->prev_poc_msb = h->poc_msb;
        h->prev_poc_lsb = h->poc_lsb;
    }
    h->prev_frame_num_offset = h->frame_num_offset;
    h->prev_frame_num        = h->frame_num;
    h->outputed_poc          = h->next_outputed_poc;

    h->recovery_frame        = h1->recovery_frame;
    h->frame_recovered       = h1->frame_recovered;

    return err;
}