Configuring servers for Ogg media
*.ogv 文件包含了视频 (也可能带有音频)，应该和
video/ogg MIME 类型一起提供。
audio/ogg MIME 类型一起提供。
如果不确定 Ogg 文件是否包含音频或视频，可以和 MIME 类型
AddType audio/ogg .oga AddType video/ogg .ogv AddType application/ogg .ogg
In order to support seeking and playing back regions of the media that aren't yet downloaded, Gecko uses HTTP 1.1 byte-range requests to retrieve the media from the seek target position. In addition, Gecko uses byte-range requests to seek to the end of the media (assuming you serve the
Content-Length header) in order to determine the duration of the media.
Your server should accept the
: bytes HTTP header if it can accept byte-range requests. It must return
: Partial content to all byte range requests; otherwise, browsers can't be sure you actually support byte range requests.
Your server must also return
206: Partial Content for the request
Range: bytes=0- as well.
When the browser seeks through Ogg media to a specified time, it has to seek to the nearest key frame before the seek target, then download and decode the video from there until the requested target time. The farther apart your key frames are, the longer this takes, so it's helpful to include key frames at regular intervals.
ffmpeg2theora uses one key frame every 64 frames (or about every 2 seconds at 30 frames per second), which works pretty well.
<video> elements provide the
preload attribute, which tells the browser to attempt to download the entire media when the page loads. Without
preload, the browser only downloads enough of the media to display the first video frame, and to determine the media's duration.
preload is off by default, so if getting to video is the point of your web page, your users may appreciate it if you include
preload in your video elements. using
preload="metadata" will preload the media file's metadata and possibly the first few frames of video. Setting
auto tells the browser to automatically begin downloading the media as soon as the page is loaded, under the assumption that the user will play it.
The Ogg format doesn't encapsulate the duration of media, so for the progress bar on the video controls to display the duration of the video, Gecko needs to determine the length of the media using other means.
There are two ways Gecko can do this. The best way is to offer an
X-Content-Duration header when serving Ogg media files. This header provides the duration of the video in seconds (not in HH:MM:SS format) as a floating-point value.
For example, if the video is 1 minute and 32.6 seconds long, this header would be:
If your server provides the
X-Content-Duration header when serving Ogg media, Gecko doesn't have to do any extra HTTP requests to seek to the end of the file to calculate its duration. This makes the entire process much more efficient as well as more accurate.
As an inferior alternative, Gecko can estimate the video length based on the Content-Length. See next point.
One common way to reduce the load on a web server is to use gzip or deflate compression when serving to a supporting web browser.
Although it's unlikely, it's possible the browser may advertise that it supports HTTP compression (gzip/deflate) using the
Accept-Encoding: gzip,deflate header when requesting media files. Your server should be configured to not do so. The data in media files is already compressed, so you won't get any real benefit from compression, and the use of compression makes it impossible for the browser to properly seek the video or determine its duration.
Another probelm with allowing HTTP compression for media streaming: Apache servers don't send the
Content-Length response header if gzip encoding is used.
You can use the
oggz-info tool to get the media duration; this tool is included with the
oggz-tools package. The output from
oggz-info looks like this:
$ oggz-info /g/media/bruce_vs_ironman.ogv Content-Duration: 00:01:00.046 Skeleton: serialno 1976223438 4 packets in 3 pages, 1.3 packets/page, 27.508% Ogg overhead Presentation-Time: 0.000 Basetime: 0.000 Theora: serialno 0170995062 1790 packets in 1068 pages, 1.7 packets/page, 1.049% Ogg overhead Video-Framerate: 29.983 fps Video-Width: 640 Video-Height: 360 Vorbis: serialno 0708996688 4531 packets in 167 pages, 27.1 packets/page, 1.408% Ogg overhead Audio-Samplerate: 44100 Hz Audio-Channels: 2
Note that you can't simply serve up the reported Content-Duration line reported by
oggz-info, because it's reported in HH:MM:SS format. You'll need to convert it to seconds only, then serve that as your
X-Content-Duration value. Just parse out the HH, MM, and SS into numbers, then do (HH*3600)+(MM*60)+SS to get the value you should report.
It's important to note that it appears that
oggz-info makes a read pass of the media in order to calculate its duration, so it's a good idea to store the duration value in order to avoid lengthy delays while the value is calculated for every HTTP request of your Ogg media.