Module ngx_http_mp4_module

The module ngx_http_mp4_module provides pseudo-streaming server-side support for H.264/AAC files typically having filename extensions .mp4, .m4v, and .m4a.

Pseudo-streaming works in alliance with conforming 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 start and specified in seconds), and the server responds with a stream so that its start position corresponds to the requested time, for example:

http://example.com/elephants_dream.mp4?start=238.88

This allows for a random seeking at any time, or starting playback in the middle of a timeline.

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.

To start playback, a player first needs to read metadata. This is done by sending a special request with the start=0 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 prepare an original file for pseudo-streaming, rather than having nginx do this on every such request.

For a matching request with a non-zero start 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.

If a matching request does not include the start 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.

This module is not built by default, it should be enabled with the --with-http_mp4_module configuration parameter.

If a third-party mp4 module was previously used, it needs to be disabled.

A similar pseudo-streaming support for FLV files is provided by the module ngx_http_flv_module.

Example Configuration

location /video/ {
    mp4;
    mp4_buffer_size     1m;
    mp4_max_buffer_size 5m;
}

Directives

Turns on module processing in a surrounding location.

mp4_buffer_size 512K;

Sets the initial size of a memory buffer used to process MP4 files.

mp4_max_buffer_size 10M;

During metadata processing, a larger buffer may become necessary. Its size cannot exceed the specified size, or else nginx will return the server error 500 (Internal Server Error), and log the following:

"/some/movie/file.mp4" mp4 moov atom is too large:
12583268, you may want to increase mp4_max_buffer_size