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<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>HTTP MP4 Module</title></head><body><center><h3>HTTP MP4 Module</h3></center><center><h4>Summary</h4></center><p>
The module <code>ngx_http_mp4_module</code> provides pseudo-streaming
server-side support for H.264/AAC files typically having filename extensions
<code>.mp4</code>, <code>.m4v</code>,
and <code>.m4a</code>.
</p><p>
Pseudo-streaming works in alliance with conformant Flash players.
A player sends an HTTP request to the server with a start time
argument in the request URI’s query string (named simply
<code>start</code>
and specified in seconds), and the server responds with a stream
so that its start position corresponds to the requested time,
for example:
<blockquote><pre>
http://example.com/elephants_dream.mp4?start=238.88
</pre></blockquote>
This allows for a random seeking at any time, or starting playback
in the middle of a timeline.
</p><p>
To support seeking, H.264-based formats store the metadata
in the so-called “moov atom.”
It is a part of the file that holds the index information for the
whole file.
</p><p>
To start playback, a player first needs to read metadata.
This is done by sending a special request with the
<code>start=0</code>
argument.  Many encoding software will insert the metadata at
the end of the file.  This is bad for pseudo-streaming:
the metadata needs to be located at the beginning of the file,
or else the entire file will have to be downloaded before it
starts playing.  If a file is well-formed (with metadata at the
beginning of a file), nginx just sends back the contents of a file.
Otherwise, it has to read the file and prepare a new stream so that
metadata comes before media data.
This involves some CPU, memory, and disk I/O overhead,
so it is a good idea to
<a href="http://flowplayer.org/plugins/streaming/pseudostreaming.html#prepare">
prepare an original file for pseudo-streaming</a>,
rather than having nginx do this on every such request.
</p><p>
For a matching request with a non-zero
<code>start</code>
argument, nginx will read metadata from the file, prepare the
stream starting from the requested offset, and send it to a client.
This has the same overhead as described above.
</p><p>
If a matching request does not include the
<code>start</code>
argument, there is no overhead, and the file is just sent as a static resource.
Some players also support byte-range requests, and thus do not require
this module at all.
</p><p>
This module is not built by default, it should be enabled with the
<code>--with-http_mp4_module</code>
configuration parameter.

If you were using the third-party mp4 module, be sure to disable it.
</p><p>
A similar pseudo-streaming support for FLV files is provided by the module
<a href="ngx_http_flv_module.html">ngx_http_flv_module</a>.
</p><a name="example"></a><center><h4>Example Configuration</h4></center><p><blockquote><pre>
location /video/ {
    mp4;
    mp4_buffer_size     1m;
    mp4_max_buffer_size 5m;
}
</pre></blockquote></p><a name="directives"></a><center><h4>Directives</h4></center><hr><a name="mp4"></a><strong>syntax</strong>:
         <code>mp4</code><br><strong>default</strong>:
      <strong>none</strong><br><strong>context</strong>:
      <code>location</code><br><p>
Turns on module processing in a surrounding location.
</p><hr><a name="mp4_buffer_size"></a><strong>syntax</strong>:
         <code>mp4_buffer_size <code><i>size</i></code></code><br><strong>default</strong>:
      <code>mp4_buffer_size 512K</code><br><strong>context</strong>:
      <code>http</code>, <code>server</code>, <code>location</code><br><p>
Sets the initial size of a memory buffer used to process MP4 files.
</p><hr><a name="mp4_max_buffer_size"></a><strong>syntax</strong>:
         <code>mp4_max_buffer_size <code><i>size</i></code></code><br><strong>default</strong>:
      <code>mp4_max_buffer_size 10M</code><br><strong>context</strong>:
      <code>http</code>, <code>server</code>, <code>location</code><br><p>
During metadata processing, a larger buffer may become necessary.
Its size cannot exceed the specified <code><i>size</i></code>,
or else nginx will return the server error
500 (Internal Server Error),
and log the following:
<blockquote><pre>
"/some/movie/file.mp4" mp4 moov atom is too large:
12583268, you may want to increase mp4_max_buffer_size
</pre></blockquote></p></body></html>
author	Ruslan Ermilov <ru@nginx.com>
date	Thu, 15 Sep 2011 08:59:38 +0000
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