Nginx and disappearing cache

I need some kind of shield server in front of my streaming server. I have very basic nginx config for that:

proxy_cache_path /localcache/nginx levels=2:2:2 keys_zone=cache:128m;

server {
    listen *:80;
    server_name _;

    proxy_cache cache;
    proxy_cache_lock on;

    # Immediately forward requests to the origin if we are filling the cache
    proxy_cache_lock_timeout 0s;

    # Set the 'age' to a value larger than the expected fill time
    proxy_cache_lock_age 5s;

    proxy_cache_valid 200 36500d;
    proxy_cache_use_stale updating;
    proxy_cache_methods GET;

    location /streamer/ {
        proxy_set_header Host streamser.server.exapmle;
        proxy_pass_request_headers off;
        proxy_hide_header Cache-Control;
        proxy_ignore_headers Cache-Control;
        proxy_ignore_headers x-accel-expires;
        proxy_ignore_headers expires;
        proxy_hide_header etag;
        proxy_http_version 1.1;
        proxy_cache_key $host$uri$is_args$args;
        proxy_set_header Connection "";
        proxy_pass https://111.222.333.444;
        add_header Set-Cookie chost=$Host;
        add_header XX-Cache-Status $upstream_cache_status;
    }
}

I want to store entries in the cache forever - just until I purge particular files manually. When I watch the video for the first time I can see that header XX-Cache-Status shows MISS as expected, I see the cache folder growing

sudo du -hs vol/localcache/nginx/
62M     vol/localcache/nginx/

when I rewind video I see that XX-Cache-Status changes to HIT - looks ok. But! After some time I find the cache folder getting smaller and smaller:

sudo du -hs vol/localcache/nginx/
42M     vol/localcache/nginx/

It looks like the cache is purging but I don't understand why. This happens when video is playing. When I stop playing I find cache folder empty in 10-15 minutes but I see no reasons for that. Please help to fix it.

The problem was in inactive parameter of proxy_cache_path directive - it's 10 minutes by default.