livesim2

README

livesim2 - the second generation DASH Live Source Simulator

livesim2 is a new and improved version of the DASH-IF live source simulator.

Test it at https://livesim2.dashif.org or set up your own server using your own DASH content or test content available at livesim-content. See the wiki for more info.

As the original simulator (livesim1), the output is a wall-clock (UTC) synchronized infinite linear stream of segments. This achieved by looping input VoD DASH assets, and changing time stamps so that an infinite "live" stream is available. The synchronization is done modulo asset duration, for example: a 1-hour asset restarts every hour on full hours, and a 30s asset restarts every 30s on full and half minutes. If there is a clock display in the video, and the length is full minutes or similar, it is therefore easy to directly see how long the system delay is from publishing to screen presentation. The very short example assets bundled with the code are only 8s long, which means that they restart every time the UTC time is a multiple of 8s, relative to the Epoch start 1970-01-01:00:00:00Z.

To provide full UTC time stamps on-screen and the possibility to test subtitles, livesim2 has a new feature for generating subtitles for any number of languages. This is done by a URL parameter like /timesubsstpp_en,sv which will result in two stpp (segmented TTML) subtitle tracks with with language codes "en" and "sv", respectively. There is a corresponding setting for wvtt (segmented WebVTT) subtitles using /timesubswvtt_en,sv.

The new livesim2 software is written in Go instead of Python and designed to handle content in a more flexible and versatile way. It is intended to be very easy to install and deploy locally since it is compiled into a single binary that serves the content via a built-in performant HTTP/2 server. There is also a very simple way of setting up HTTPS using Let´s Encrypt.

Similarly to livesim1, the output is highly configurable by adding parameters inside the URLs. These parameters are included not only in the MPD requests, but in all segment requests allowing the server to be stateless, and be able to generate streams with a huge number of parameter variations. Currently, not all parameters of livesim1 are implemented, but there are also new parameters like the generated subtitles mentioned above.

The URL wiki page lists what is available and the served page /urlgen makes it easy to construct URLs to play the content with specific parameters set.

Beside livesim2 there is a tool called dashfetcher in this repo. That tool can be used to download the MPD and all segments of a DASH VoD asset.

livesim2 server

The server is configured in one or more ways in increasing priority:

1. Default values
2. In a config file
3. Via command-line parameters
4. With environment variables

Major values to configure are:

• the top directory vodroot for searching for VoD assets to be used
• the HTTPS domains if Let's Encrypt automatic certificates are used
  • certpath and keypath if HTTPS is used with manually downloaded certificates
  • the HTTP/HTTPS port if domains is not being used (default: 8888)

Once the server is started, it will scan the file tree starting from vodroot and gather metadata about all DASH VoD assets it finds. Currently, only source VoD assets using SegmentTimeline with $Time$ and SegmentTemplate with $Number$ are supported.

Command-line parameters

A complete list of parameters, and their access via the command line looks like:

  --certpath string      path to TLS certificate file (for HTTPS). Use domains instead if possible
  --cfg string           path to a JSON config file
  --domains string       One or more DNS domains (comma-separated) for auto certificate from Lets Encrypt
  --host string          host (and possible prefix) used in MPD elements. Overrides auto-detected full scheme://host
  --keypath string       path to TLS private key file (for HTTPS). Use domains instead if possible.
  --livewindow int       default live window (seconds) (default 300)
  --logformat string     log format [text, json, pretty, discard] (default "text")
  --loglevel string      log level [DEBUG, INFO, WARN, ERROR] (default "INFO")
  --maxrequests int      max nr of request per IP address per 24 hours
  --playurl string       URL template to play mpd. %s will be replaced by MPD URL (default "https://reference.dashif.org/dash.js/latest/samples/dash-if-reference-player/index.html?mpd=%s&autoLoad=true&muted=true")
  --port int             HTTP port (default 8888)
  --repdataroot string   Representation metadata root directory. "+" copies vodroot value. "-" disables usage. (default "+")
  --reqlimitint int      interval for request limit i seconds (only used if maxrequests > 0) (default 86400)
  --reqlimitlog string   path to request limit log file (only written if maxrequests > 0)
  --scheme string        scheme used in Location and BaseURL elements. If empty, it is attempted to be auto-detected
  --timeout int          timeout for all requests (seconds) (default 60)
  --vodroot string       VoD root directory (default "./vod")
  --writerepdata         Write representation metadata if not present

Quicker load by using metadata files

For assets with many segments, the scanning process can take a considerable time. The possibility to generate and read extra representation metadata files has therefore been added. For representation repX, the corresponding metadata file is repX_data.json.gz. As the file extensions indicates, these files are gzipped JSON files. To generate such files, the option writerepdata must be on. The root directory for such files is by default the same as the VoD root directory, meaning that the metadata files will be in the same directories as the corresponding MPDs. However, it is possible to use another path, by specifying repdataroot.

Once the server has started, it is possible to find out information about the server and the assets using the root HTTP endpoint

• /

that in turn points to:

• /urlgen
• /assets
• /config
• /healthz
• /metrics

and links to the Wiki page for more information.

It is also possible to explore the file tree and play Vod assets by starting at

• /vod/...

Finally, any VoD MPD like /vod/cfhd/stream.mpd is available as a live stream by replacing /vod/ with livesim2 e.g. /livesim2/cfhd/stream.mpd.

Backwards compatibility with livesim

For backwards compatibility with the first version of livesim where /livesim was used as a prefix for simulated live output, and /dash/vod was the path to the VoD assets, these two paths are redirected by the server with an HTTP 302 response as:

/livesim/* -> /livesim2/*
/dash/vod/* -> /vod/*

MPD Restrictions

The following restrictions apply to the VoD manifest to be used with livesim2

• live-profile (separate segments)
• one Period with all representations of "same" duration
• no BaseURL elements
• no Location elements
• initialization and media attributes in SegmentTemplate on AdaptationSet level

Special Time Test Parameter nowMS

The query string parameter ?nowMS=... can be used in any request to set the wall-clock time that livesim2 uses as reference time. The time is measured with respect to the 1970 Epoch start, and makes it possible to test time-dependent requests in a deterministic way.

Get Started

Install Go 1.19 or later.

Then run

> go mod tidy

(or go mod vendor)

to fetch and install all dependencies.

To build dashfetcher and livesim2 you can use the Makefile like

> make build

to create binaries in the /out directory with embedded version numbers.

During development it may be easier to use the usual go commands:

> cd cmd/dashfetcher
> go build .
> cd ../../cmd/livesim2
> go build .

or compile and run directly with go run ..

HTTPS with automatic certificates

To enable HTTPS in an easy manner, make sure that you have DNS pointing to your machine, and that ports 80 and 443 are forwarded. Then use the parameter --domains=your.domain.com,second.domain.com to automatically fetch TLS certificates from Let's Encrypt for your domains to this machine. The certificates are automatically renewed before they expire.

HTTPS with manual certificates

The old-fashioned way of using manually acquired TLS certificates is also supported. Use the two parameters certpath and keypath to point to the respective files, and set the port to 443.`

Content

The content must be a DASH VoD asset in isoff-live format (individual segment files) with either SegmentTimeline with $Time$ or SegmentTemplate with $Number$. The video segment duration must be constant and an integral number of milliseconds. Audio output segments will be adjusted to start at, or less than one audio frame after, each video segment start.

There are multiple ways to get content to the livesim2 server.

1. Use the bundled test content (only 8s long)
2. Fetch content that was used with livesim1 from github at livesim-content
3. Use the dashfetcher tool to download a DASH asset
4. Copy an existing VoD asset in isoff-live

There is special representation data that can be used for quicker loading of the assets. The generation of such data is controlled via the writerepdata and repdataroot configuration parameters.

Bundled test streams with the livesim2 server

A few very short (8s) test assets are bundled with the code. These makes it possible to start the server and get live output by running

> cd cmd/livesim2
> ./livesim2 --vodroot=app/testdata/assets

The log will list the available assets and the port where the server runs.

They can then be streamed via URLs like:

http://localhost:8888/livesim2/WAVE/vectors/cfhd_sets/12.5_25_50/t3/2022-10-17/stream.mpd
http://localhost:8888/livesim2/testpic_2s/Manifest_thumbs.mpd
http://localhost:8888/livesim2/testpic_8s/Manifest.mpd

The default pattern provides MPDs with SegmentTemplate using $Number$. To stream with SegmentTimeline with $Time$, one should add the parameter /segtimeline_1 between livesim2 and the start of the asset path. For SegmentTimeline with $Number$, use /segtimelinenr_1 instead. Other parameters are added in a similar way.

Adding longer assets somewhere under the vodroot results in longer loops. All sources are NTP synchronized (using the host machine clock) with a initial start time given by availabilityStartTime and wrap every sequence duration after that.

livesim-content at Github

In the repo livesim-content, the content that was used for the livesim1 online service is being gathered to make it easy to reproduce the same use cases.

All content and features are not yet (2023-08-08) in place, but should be so before end of October 2023.

To download and use that content, run

git clone https://github.com/Dash-Industry-Forum/livesim-content.git

and then set --vodroot to the livesim-content top directory or include that in a bigger file tree.

dashfetcher tool

The tool dashfetcher fetches DASH VoD assets via HTTP given an MPD URLs. Currently it supports MPDs with SegmentTimeline with $Time$ and SegmentTemplate with $Number$. The assets must have no explicit <BaseURL> elements to work properly. With the -a/--auto option, the path to the asset is preserved as much as possible and adapted to the local path.

Files already downloaded will not be downloaded again, unless -f/--force is used. As an example, to download a CTA-WAVE asset one can run

dashfetcher --auto https://dash.akamaized.net/WAVE/vectors/cfhd_sets/12.5_25_50/t3/2022-10-17/stream.mpd

which will result in a locally stored DASH VoD asset in the directory

./vod/WAVE/vectors/cfhd_sets/12.5_25_0t3/2022-10-17/

with an MPD called stream.mpd and the segments stored in subdirectories named after their relative URLs. The download URL is added to a file mpdlist.json which is read by livesim2, to provide information about the asset.

One can have multiple MPDs in the same asset directory and they may share some representations. That is an easy way to have variants with different representation combinations.

Running dashfetcher

dashfetcher was created to facilitate download of DASH assets with lots of small segment files. One particular such source was the CTA-WAVE test content. However, that content is now also available as zip-files, so it is more efficient to download an unzip these files instead of making individual downloads of the segments.

For example, the asset above is also available at https://dash.akamaized.net/WAVE/vectors/cfhd_sets/12.5_25_50/t3/2022-10-17/t3.zip.

The dashfetcher binary can be found as out/dashfetcher after make build.

> dashfetcher --help

will provide a long help text that explains how to use it and will also provide an example URL to CTA-WAVE content.

Running tests

The unit tests can be run from the top directory with the usual recursive Go test command go test ./... or with the make targets for testing, linting, and coverage:

> make test
> make check
> make coverage

Deployment

Both dashfetcher and livesim2 can be compiled to single binaries on any Go compiler target platform such as Windows, MacOS, and Linux. Since the result is a single binary it is easy to start it anywhere.

On Linux, livesim2 can be run as a systemd service. More information can be found in the deployment/README.md file.

To get information about the available assets and other information access the server's root URL.

Docker

A simple Dockerfile is also provided. It builds a stand-alone livesim2 image bundled with the test content that is provided in this repo. Some comments are included in the Dockerfile. Check the options of livesim2 to find out how to add other content, HTTPs etc.

List of functionality and options

The most direct information about the URL parameters and how to find them, is available via the urlgen page that can be reached once the server is running. The livesim2 online page is urlgen.

The URL parameters are also listed on this project's Wiki page URL-parameters. Some more information about how they are working is also available on the Wiki.

Project and plan for new features/enhancement

The sponsored transition from livesim to livesim2 is covered on a wiki page. On the livesim2 project page the status of issues and proposed new ideas are listed. Draft ideas are changed into livesim2 issues if prioritized.

Sponsoring

It is possible to sponsor the project for further development. See the SPONSORING.md file for more information.

License

See LICENSE.md.