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v2l-example-scheduler

This is example code to show how to use the REST API of the Agile Content/Edgeware ESB-3019 ew-vod2cbm service to provide a linear channel with a schedule which is updated as time passes.

Description

This simple scheduling service generates and updates the schedule of linear channel from VoD assets and ads. The schedule is posted to a ew-vod2cbm service, that serves the actual channel via HTTP to a StreamBuilder repackager. Every second entry in the schedule is an ad, and every second a program. The entries are added randomly among the assets found in the assets directory, and are classified as ads or programs depending on their paths. In a true CMS system, there may of course be more metadata about each asset.

One does not need to schedule the whole asset. With the offset and length attributes in the schedule JSON structure, one can choose any interval of an asset, or even extend it to be looped by specifying a length that goes beyond its end. This is used to schedule partial assets at the start of the schedule.

The program keeps a sliding window and adds entries to the end of the schedule, while removing entries from the past as they are moved out of the accessible window. The window, as many other parameters, are measured in number of GoPs. These values are set as constants in main.go.

Below is a sequence diagram showing the communication between this scheduler and a vod2cbm server.

sequenceDiagram
    participant v2ls as v2l-example-scheduler
    participant vod2cbm as ew-vod2cbm
    participant storage
    v2ls->>vod2cbm: DELETE ch1
    Note right of vod2cbm: delete any previous version
    v2ls->>vod2cbm: DELETE assetpaths
    Note right of vod2cbm: only asset paths not in any schedule can be removed
    v2ls->>storage: read asset directories
    v2ls->>vod2cbm: POST assetpaths
    Note right of vod2cbm: asset paths must be added before they are scheduled
    v2ls->>v2ls: CreateChannel()
    v2ls->>vod2cbm: POST ch1
    vod2cbm->>storage: Load assets in schedule
    v2ls->>vod2cbm: GET schedule/ch1
    Note right of vod2cbm: The returned schedule includes asset lengths
    loop Timer
        v2ls->>v2ls: updateSchedule
        v2ls->>vod2cbm: PUT schedule/ch1
    end
Loading

The ew-vod2cbm server has a Swagger front-end available at http://localhost:8090/swagger. For testing purposes, one can also stream HLS directly from the server at the URL http://localhost:8090/ch1/index.html.

The assets

In general, all assets need to be coded in the same way and all video must have the same GoP durations. The segment length can be any integral multiple of the GoP duration since each segment is built from GoPs.

A further restriction is that all content must be in either Edgeware ESF format or in DASH OnDemand format. ESF is a CMAF-based format but with some additional metadata in form of a content_info.json file and some binary .dat files. Each such asset must be accessible via a file path, HTTP URL or on an S3 bucket.

The example content in this repo all have a GoP duration of 2000ms.

Compatibility

This example scheduler should work towards all versions of ew-vod2cbm. The ew-vod2cbm server is assumed to be at localhost:8090, but another address, can be set in the main.go file. The ew-vod2cbm must have access to the assets directory. The path is set in the main.go file. The default is a local directory named assets, but one could instead use another directory or an HTTP location.

The media tracks being produced are described in the content template file content_template.json, and the input tracks must be compatible with that template (for more about compatibility, check the documentation for ew-vod2cbm).

How to run the program

You need to have an ESB-3015/ew-vod2cbm server running at localhost:8090. It does not need a config file, since everything it needs is sent via HTTP from this scheduler.

To compile the program you need go installed. You can also get a compiled binary that you can run on any platform.

The project has no dependencies on other repos, so the binary can be built by simply running

$ go build .

which will build the binary v2l-example-scheduler.

Alternatively, you can run it without building it as

 $ go run .

In both cases, there are currently no command-line parameters.

Checking the EPG

A very simple EPG is available at http://localhost:8090/epg/ch1.

Further documentation

The ew-vod2cbm documentation is available online at https://docs.agilecontent.com/docs/acp/esb3019.