90 lines
4.3 KiB
HTML
90 lines
4.3 KiB
HTML
<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>
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The module <code>ngx_http_mp4_module</code> provides pseudo-streaming
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server-side support for H.264/AAC files typically having filename extensions
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<code>.mp4</code>, <code>.m4v</code>,
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and <code>.m4a</code>.
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</p><p>
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Pseudo-streaming works in alliance with conformant Flash players.
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A player sends an HTTP request to the server with a start time
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argument in the request URI’s query string (named simply
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<code>start</code>
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and specified in seconds), and the server responds with a stream
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so that its start position corresponds to the requested time,
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for example:
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<blockquote><pre>
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http://example.com/elephants_dream.mp4?start=238.88
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</pre></blockquote>
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This allows for a random seeking at any time, or starting playback
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in the middle of a timeline.
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</p><p>
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To support seeking, H.264-based formats store the metadata
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in the so-called “moov atom.”
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It is a part of the file that holds the index information for the
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whole file.
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</p><p>
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To start playback, a player first needs to read metadata.
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This is done by sending a special request with the
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<code>start=0</code>
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argument. Many encoding software will insert the metadata at
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the end of the file. This is bad for pseudo-streaming:
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the metadata needs to be located at the beginning of the file,
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or else the entire file will have to be downloaded before it
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starts playing. If a file is well-formed (with metadata at the
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beginning of a file), nginx just sends back the contents of a file.
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Otherwise, it has to read the file and prepare a new stream so that
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metadata comes before media data.
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This involves some CPU, memory, and disk I/O overhead,
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so it is a good idea to
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<a href="http://flowplayer.org/plugins/streaming/pseudostreaming.html#prepare">
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prepare an original file for pseudo-streaming</a>,
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rather than having nginx do this on every such request.
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</p><p>
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For a matching request with a non-zero
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<code>start</code>
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argument, nginx will read metadata from the file, prepare the
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stream starting from the requested offset, and send it to a client.
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This has the same overhead as described above.
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</p><p>
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If a matching request does not include the
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<code>start</code>
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argument, there is no overhead, and the file is just sent as a static resource.
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Some players also support byte-range requests, and thus do not require
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this module at all.
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</p><p>
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This module is not built by default, it should be enabled with the
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<code>--with-http_mp4_module</code>
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configuration parameter.
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If you were using the third-party mp4 module, be sure to disable it.
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</p><p>
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A similar pseudo-streaming support for FLV files is provided by the module
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<a href="ngx_http_flv_module.html">ngx_http_flv_module</a>.
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</p><a name="example"></a><center><h4>Example Configuration</h4></center><p><blockquote><pre>
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location /video/ {
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mp4;
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mp4_buffer_size 1m;
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mp4_max_buffer_size 5m;
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}
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</pre></blockquote></p><a name="directives"></a><center><h4>Directives</h4></center><hr><a name="mp4"></a><strong>syntax</strong>:
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<code>mp4</code><br><strong>default</strong>:
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<strong>none</strong><br><strong>context</strong>:
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<code>location</code><br><p>
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Turns on module processing in a surrounding location.
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</p><hr><a name="mp4_buffer_size"></a><strong>syntax</strong>:
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<code>mp4_buffer_size <code><i>size</i></code></code><br><strong>default</strong>:
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<code>mp4_buffer_size 512K</code><br><strong>context</strong>:
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<code>http</code>, <code>server</code>, <code>location</code><br><p>
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Sets the initial size of a memory buffer used to process MP4 files.
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</p><hr><a name="mp4_max_buffer_size"></a><strong>syntax</strong>:
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<code>mp4_max_buffer_size <code><i>size</i></code></code><br><strong>default</strong>:
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<code>mp4_max_buffer_size 10M</code><br><strong>context</strong>:
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<code>http</code>, <code>server</code>, <code>location</code><br><p>
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During metadata processing, a larger buffer may become necessary.
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Its size cannot exceed the specified <code><i>size</i></code>,
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or else nginx will return the server error
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500 (Internal Server Error),
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and log the following:
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<blockquote><pre>
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"/some/movie/file.mp4" mp4 moov atom is too large:
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12583268, you may want to increase mp4_max_buffer_size
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</pre></blockquote></p></body></html>
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