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author | Ruslan Ermilov <ru@nginx.com> |
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date | Thu, 15 Sep 2011 08:59:38 +0000 |
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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>