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view xml/en/docs/http/ngx_http_mp4_module.xml @ 1100:287c2a9c9d63
Added spdy2 advisory link.
author | Maxim Dounin <mdounin@mdounin.ru> |
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date | Tue, 18 Mar 2014 22:11:32 +0400 |
parents | f34be6b26447 |
children | 1fcf8c840dbe |
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<?xml version="1.0"?> <!-- Copyright (C) Nginx, Inc. --> <!DOCTYPE module SYSTEM "../../../../dtd/module.dtd"> <module name="Module ngx_http_mp4_module" link="/en/docs/http/ngx_http_mp4_module.html" lang="en" rev="2"> <section id="summary"> <para> The <literal>ngx_http_mp4_module</literal> module provides pseudo-streaming server-side support for H.264/AAC files. Such files typically have the <path>.mp4</path>, <path>.m4v</path>, or <path>.m4a</path> filename extensions. </para> <para> The pseudo-streaming works in alliance with a compatible Flash players. A player sends an HTTP request to the server with a start time specified in the query string argument (named simply <literal>start</literal> and specified in seconds), and the server responds with the stream such that its start position corresponds to the requested time, for example: <example> http://example.com/elephants_dream.mp4?start=238.88 </example> This allows performing a random seeking at any time, or starting playback in the middle of the timeline. </para> <para> 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. </para> <para> To start playback, a player first needs to read metadata. This is done by sending a special request with the <literal>start=0</literal> argument. Much of encoding software will insert the metadata at the end of the file. This is bad for pseudo-streaming: the metadata should be located at the beginning of the file, or else the entire file will have to be downloaded to start playing. If a file is well-formed (with metadata at the beginning of a file), nginx just sends back the file contents. Otherwise, it has to read the file and prepare a new stream so that the metadata comes before the media data. This involves some CPU, memory, and disk I/O overhead, so it is a good idea to <link url="http://flowplayer.org/plugins/streaming/pseudostreaming.html#prepare"> prepare an original file for pseudo-streaming</link>, rather than having nginx do this on every such request. </para> <para> For a matching request with a non-zero <literal>start</literal> argument, nginx will read the 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. </para> <para> If a matching request does not include the <literal>start</literal> 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. </para> <para> This module is not built by default, it should be enabled with the <literal>--with-http_mp4_module</literal> configuration parameter. <note> If a third-party mp4 module was previously used, it should be disabled. </note> </para> <para> A similar pseudo-streaming support for FLV files is provided by the <link doc="ngx_http_flv_module.xml">ngx_http_flv_module</link> module. </para> </section> <section id="example" name="Example Configuration"> <para> <example> location /video/ { mp4; mp4_buffer_size 1m; mp4_max_buffer_size 5m; mp4_limit_rate on; mp4_limit_rate_after 30s; } </example> </para> </section> <section id="directives" name="Directives"> <directive name="mp4"> <syntax/> <default/> <context>location</context> <para> Turns on module processing in a surrounding location. </para> </directive> <directive name="mp4_buffer_size"> <syntax><value>size</value></syntax> <default>512K</default> <context>http</context> <context>server</context> <context>location</context> <para> Sets the initial size of a memory buffer used for processing MP4 files. </para> </directive> <directive name="mp4_max_buffer_size"> <syntax><value>size</value></syntax> <default>10M</default> <context>http</context> <context>server</context> <context>location</context> <para> During metadata processing, a larger buffer may become necessary. Its size cannot exceed the specified <value>size</value>, or else nginx will return the <http-status code="500" text="Internal Server Error"/> server error, and log the following message: <example> "/some/movie/file.mp4" mp4 moov atom is too large: 12583268, you may want to increase mp4_max_buffer_size </example> </para> </directive> <directive name="mp4_limit_rate"> <syntax> <literal>on</literal> | <literal>off</literal> | <value>factor</value></syntax> <default>off</default> <context>http</context> <context>server</context> <context>location</context> <para> Enables or disables rate limiting based on the average bitrate of the MP4 file served. To calculate the rate, the bitrate is multiplied by the specified <value>factor</value>. The special value “<literal>on</literal>” corresponds to the factor of 1.1. </para> <para> <note> This directive is available as part of our <commercial_version/>. </note> </para> </directive> <directive name="mp4_limit_rate_after"> <syntax><value>time</value></syntax> <default>1m</default> <context>http</context> <context>server</context> <context>location</context> <para> Limits the rate after sending the specified amount of media data. </para> <para> <note> This directive is available as part of our <commercial_version/>. </note> </para> </directive> </section> </module>