Media Delivery

Overview

Media Delivery allows you to define how the CDN treats a variety of different media types including Flash media.

Flash Pseudo Streaming

Flash Pseudo Streaming allows you to define how the CDN delivers Flash media.

Initial Bytes Parameter

This is the name of the query string parameter used to specify the initial bytes of a video that should be returned before sending the requested byte offset. Typically players use ib for this query string parameter.

Frame Start Offset Parameter

This is the name of the query string parameter used to specify the specific byte offset into the requested video. Typically players use fs for this query string parameter.

Reserved Query String Parameters

Reserved Query String Parameters allows you to define special query string parameters the CDN will use to alter responses.

Content-Disposition File Name Query String Parameter

This is the query string parameter name which will specify the filename used in the Content-Disposition header when it's enabled.

Content-Disposition Type

This is the query string parameter name which will specify the type (inline or attachment) used in the Content-Disposition header when it's enabled.

Content-Disposition Header Override

This is the query string parameter name which will override the whole value in the Content-Disposition header.

Pseudo Streaming

Pseudo Streaming allows you to enable Flash-based video players to support seeking to random locations within an MP4 or FLV file without having to download the entire video. 

Flash players such as Flowplayer and JWPlayer can be configured to send a query string parameter that indicates to the server the time offset the user advanced the video to. Typically a query string parameter named start is used by these players.

Note that the CDN supports range requests to the HTTP specification here.

Jump-to-Time

For H.264-encoded videos, the Highwinds CDN natively supports a jump-to-time feature on the CDS platform, allowing you to seek to a portion of the video that may not yet be downloaded. Simply add a URL parameter named "start" and a timestamp (in seconds), and the CDN will deliver the stream from that point forward. The start parameter is used by default for Jump-to-Time functionality, however that parameter name is configurable on the CDN. In many instances, FLVs with enhanced metadata also support this Jump-to-Time functionality.

When using the jump-to-time for videos such as .MP4, there is often a moov atom that contains necessary metadata about the video. For fast seeking to portions of the video that have not yet been downloaded, this "moov" atom will need to be present at the beginning of the video rather than the end. Tools are available to reposition the moov atom within an existing video.

Jump-to-Byte

Some types of videos (such as metadata-enhanced FLVs) can be enabled with progressive seek functionality via the "jump-to-byte" approach. When using Jump-to-Byte, there are two query string parameters than can be utilized. The ib query string parameter is used to specify the initial bytes of a video that should be returned before sending the requested byte offset. The "fs" query string parameter is used to specify the specific byte offset into the requested video. The parameter names ib and fs" are used by default on the CDN, however these names are configurable.

In order for this jump-to-byte process to work, your FLVs must have metadata within them (specifically the “keyframes” element). If they don’t today, download FLVMDI of FFMPEG and run it against each of your files with the /k switch (this will inject the keyframe metadata): http://www.buraks.com/flvmdi

If you already have the metadata needed for each video, then you should have an xml file that has a list of file positions and time codes for all of the keyframes in the video. You basically need to have is a mapping between times and the keyframes that are the closest to those times. This is accomplished by mapping the time indexes in the times array to the keyframe indexes in the filepositions array. Both of these arrays are found on the keyframes metadata element.

Note that there are a few ways to accomplish this:

1) You can do it all in the player:

1. Initially load the file from the beginning, which will cause the onMetaData handler to fire as soon as the metadata is read from the file's header.
2. Within the onMetaData handler, load the time indexes and keyframe file positions into a lookup table.
3. When a scrubbing event occurs, use the lookup table to find the file position of the keyframe that most closely matches the time index that you passed in.
4. Re-request the file with the ib=13&fs=<keyframe> parameters.

Leave the ib=13 on for all requests (both the ib and fs parameters are optional for the initial request).

2) You can do it all on the server:

1. Run FLVMDI with both the /k and the /x switch, which will output an XML file containing all of the keyframe data.
2. Import the keyframe file positions and the times (there should be the same number of elements in each array) into your database.
3. When a scrubbing event occurs for non-downloaded portions of the file, make a call back to the server for the new fs parameter values.
4. Write a simple server-side web service call that finds the closest keyframe to the time index that you are looking for, and returns it when called.
5. Re-request the file with the ib=13&fs=<keyframe>parameters.

3) Or you can perform a hybrid of the two:

1. Run FLVMDI with both the /k and the /x switch, which will output an XML file containing all of the keyframe data.
2. Import the keyframe file positions and the times (there should be the same number of elements in each array) into your database.
3. When generating the player page for the selected video, include data in the page itself that will allow the player to do the lookup without needing to build the index using information from the onMetaData event.
4. When a scrubbing event occurs, use the lookup table to find the file position of the keyframe that most closely matches the time index that you passed in.
5. Re-request the file with the ib=13&fs=<keyframe> parameters.