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view docs/xml/http/ngx_http_mp4_module.xml @ 4141:a18b10aea510
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author | Ruslan Ermilov <ru@nginx.com> |
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date | Tue, 20 Sep 2011 13:15:41 +0000 |
parents | d889195c8db4 |
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<?xml version="1.0"?> <!DOCTYPE module SYSTEM "../../dtd/module.dtd"> <module name="HTTP MP4 Module" id="http_mp4_module"> <section name="Summary"> <para> The module <code>ngx_http_mp4_module</code> provides pseudo-streaming server-side support for H.264/AAC files typically having filename extensions <pathname>.mp4</pathname>, <pathname>.m4v</pathname>, and <pathname>.m4a</pathname>. </para> <para> 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 <parameter>start</parameter> and specified in seconds), and the server responds with a stream so that its start position corresponds to the requested time, for example: <example> http://example.com/elephants_dream.mp4?start=238.88 </example> This allows for a random seeking at any time, or starting playback in the middle of a 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 <parameter>start=0</parameter> 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 <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 <parameter>start</parameter> 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. </para> <para> If a matching request does not include the <parameter>start</parameter> 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 <code>--with-http_mp4_module</code> configuration parameter. <note> If you were using the third-party mp4 module, be sure to disable it. </note> </para> <para> A similar pseudo-streaming support for FLV files is provided by the module <link doc="ngx_http_flv_module.xml">ngx_http_flv_module</link>. </para> </section> <section id="example" name="Example Configuration"> <para> <example> location /video/ { mp4; mp4_buffer_size 1m; mp4_max_buffer_size 5m; } </example> </para> </section> <section id="directives" name="Directives"> <directive name="mp4"> <syntax>mp4</syntax> <default/> <context>location</context> <para> Turns on module processing in a surrounding location. </para> </directive> <directive name="mp4_buffer_size"> <syntax>mp4_buffer_size <argument>size</argument></syntax> <default>mp4_buffer_size 512K</default> <context>http</context> <context>server</context> <context>location</context> <para> Sets the initial size of a memory buffer used to process MP4 files. </para> </directive> <directive name="mp4_max_buffer_size"> <syntax>mp4_max_buffer_size <argument>size</argument></syntax> <default>mp4_max_buffer_size 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 <argument>size</argument>, or else nginx will return the server error <http-status code="500" text="Internal Server Error"/>, and log the following: <example> "/some/movie/file.mp4" mp4 moov atom is too large: 12583268, you may want to increase mp4_max_buffer_size </example> </para> </directive> </section> </module>