int ff_slice_thread_init(AVCodecContext *avctx)
{
    int i;
    SliceThreadContext *c;
    int thread_count = avctx->thread_count;

#if HAVE_W32THREADS
    w32thread_init();
#endif

    // We cannot do this in the encoder init as the threads are created before
    if (av_codec_is_encoder(avctx->codec) &&
        avctx->codec_id == AV_CODEC_ID_MPEG1VIDEO &&
        avctx->height > 2800)
        thread_count = avctx->thread_count = 1;

    if (!thread_count) {
        int nb_cpus = av_cpu_count();
        if  (avctx->height)
            nb_cpus = FFMIN(nb_cpus, (avctx->height+15)/16);
        // use number of cores + 1 as thread count if there is more than one
        if (nb_cpus > 1)
            thread_count = avctx->thread_count = FFMIN(nb_cpus + 1, MAX_AUTO_THREADS);
        else
            thread_count = avctx->thread_count = 1;
    }

    if (thread_count <= 1) {
        avctx->active_thread_type = 0;
        return 0;
    }

    c = av_mallocz(sizeof(SliceThreadContext));
    if (!c)
        return -1;

    c->workers = av_mallocz_array(thread_count, sizeof(pthread_t));
    if (!c->workers) {
        av_free(c);
        return -1;
    }

    avctx->internal->thread_ctx = c;
    c->current_job = 0;
    c->job_count = 0;
    c->job_size = 0;
    c->done = 0;
    pthread_cond_init(&c->current_job_cond, NULL);
    pthread_cond_init(&c->last_job_cond, NULL);
    pthread_mutex_init(&c->current_job_lock, NULL);
    pthread_mutex_lock(&c->current_job_lock);
    for (i=0; i<thread_count; i++) {
        if(pthread_create(&c->workers[i], NULL, worker, avctx)) {
           avctx->thread_count = i;
           pthread_mutex_unlock(&c->current_job_lock);
           ff_thread_free(avctx);
           return -1;
        }
    }

    thread_park_workers(c, thread_count);

    avctx->execute = thread_execute;
    avctx->execute2 = thread_execute2;
    return 0;
}