v0.20.0

micro-optimization:
===================

* when all of the following are true:
  - the HLS manifest for a live stream is proxied
  - prefetch is enabled
  - the cache is empty
* rather than:
  - immediately initiating (up to "--max-segments") parallel downloads to populate the cache,
    while the video player waits for the 1st video segment to become available
* modify the order of downloads such that:
  - the 1st video segment in the manifest is immediately downloaded
  - once this 1st video segment is available,
    then all of the remaining (up to "--max-segments") in the manifest begin to download in parallel

reason for change:
==================

* this should reduce the latency when a live video first starts playing,
  since the 1st video segment downloads more quickly using all available bandwidth
* when a batch of downloads occur in parallel,
  the available bandwidth is shared (more or less) equally;
  all downloads occur at a reduced rate, and complete at about the same time

cross-reference:
================

* related discussion in issue #15

hls-proxy/proxy.js

@@ -191,10 +191,29 @@ const proxy = function({server, host, is_secure, req_headers, req_options, hooks
     // only used with prefetch
     const perform_prefetch = (cache_segments)
       ? (urls, dont_touch_access) => {
-          urls.forEach((matching_url, index) => {
-            prefetch_segment(m3u8_url, matching_url, referer_url, dont_touch_access)
+          if (!urls || !Array.isArray(urls) || !urls.length)
+            return
 
-            urls[index] = undefined
+          let promise
+
+          if (is_vod || has_cache(m3u8_url)) {
+            promise = Promise.resolve()
+          }
+          else {
+            const matching_url = urls[0]
+            urls[0] = undefined
+
+            promise = prefetch_segment(m3u8_url, matching_url, referer_url, dont_touch_access)
+          }
+
+          promise.then(() => {
+            urls.forEach((matching_url, index) => {
+              if (matching_url) {
+                prefetch_segment(m3u8_url, matching_url, referer_url, dont_touch_access)
+
+                urls[index] = undefined
+              }
+            })
           })
         }
       : null

hls-proxy/segment_cache.js

@@ -142,7 +142,9 @@ module.exports = function({should_prefetch_url, debug, debug_level, request, get
   }
 
   const prefetch_segment = function(m3u8_url, url, referer_url, dont_touch_access) {
-    if (! should_prefetch_url(url)) return
+    let promise = Promise.resolve()
+
+    if (! should_prefetch_url(url)) return promise
 
     if (cache[m3u8_url] === undefined) {
       // initialize a new data structure
@@ -165,7 +167,7 @@ module.exports = function({should_prefetch_url, debug, debug_level, request, get
       ts[index] = {key: get_privatekey_from_url(url), databuffer: false}
 
       let options = get_request_options(url, referer_url)
-      request(options, '', {binary: true, stream: false})
+      promise = request(options, '', {binary: true, stream: false})
       .then(({response}) => {
         debug(1, `prefetch (complete, ${response.length} bytes):`, debug_url)
 
@@ -201,6 +203,8 @@ module.exports = function({should_prefetch_url, debug, debug_level, request, get
         if (index !== undefined) ts_garbage_collect(m3u8_url, index, 1)
       })
     }
+
+    return promise
   }
 
   const get_segment = function(url) {

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@warren-bank/hls-proxy",
   "description": "Node.js server to proxy HLS video streams",
-  "version":     "0.19.0",
+  "version":     "0.20.0",
   "scripts": {
     "start":     "node hls-proxy/bin/hlsd.js",
     "sudo": "sudo node hls-proxy/bin/hlsd.js"