--- a/xml/en/docs/http/ngx_http_mp4_module.xml	Fri Nov 12 20:16:05 2021 +0000
+++ b/xml/en/docs/http/ngx_http_mp4_module.xml	Mon Nov 15 12:52:47 2021 +0000
@@ -9,7 +9,7 @@
 <module name="Module ngx_http_mp4_module"
         link="/en/docs/http/ngx_http_mp4_module.html"
         lang="en"
-        rev="8">
+        rev="9">
 
 <section id="summary">
 
@@ -82,6 +82,18 @@
 This has the same overhead as described above.
 </para>
 
+<para id="keyframe">
+If the <literal>start</literal> argument points to
+a non-key video frame,
+the beginning of such video will be broken.
+To fix this issue, the video
+<link id="mp4_start_key_frame">can</link> be prepended with
+the key frame before <literal>start</literal> point
+and with all intermediate frames between them.
+These frames will be hidden from playback
+using an edit list (1.21.4).
+</para>
+
 <para>
 If a matching request does not include the
 <literal>start</literal> and <literal>end</literal>
@@ -231,6 +243,26 @@
 
 </directive>
 
+
+<directive name="mp4_start_key_frame">
+<syntax><literal>on</literal> | <literal>off</literal></syntax>
+<default>off</default>
+<context>http</context>
+<context>server</context>
+<context>location</context>
+<appeared-in>1.21.4</appeared-in>
+
+<para>
+Forces output video to always start with a key video frame.
+If the <literal>start</literal> argument does not point to a key frame,
+initial frames are hidden using an mp4 edit list.
+Edit lists are supported by major players and browsers such as
+Chrome, Safari, QuickTime and ffmpeg,
+partially supported by Firefox.
+</para>
+
+</directive>
+
 </section>
 
 </module>