livesim2 is a new and improved version of the
DASH-IF live source simulator.
As the original simulator (livesim1), the output is a wall-clock (UTC) synchronized infinite linear stream of segments. The synchronization is done modulo asset length, 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 in the video, 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 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 subtitle tracks with with language codes "en" and "sv", respectively.
The new 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 tool called dashfetcher that can be used to download
DASH VoD assets that can serve as sources for the live
linear outputs.
The sources are looped so that an infinite "live" stream is available.
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 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.
There are two main components, the server livesim2 and the VoD fetcher
dashfetcher.
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.mpdwhich 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.
The server is configured in one or more ways in increasing priority:
- Default values
- In a config file
- Via command-line parameters
- With environment variables
Major values to configure are:
- the HTTP port being used (default: 8888)
- the top directory
vodrootfor searching for VoD assets to be used certpathandkeypathis the HTTPS is used
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 VoD assets using SegmentTimeline with $Time$ and
SegmentTemplate with $Number$ are supported.
Once the server has started, it is possible to find out information about the server and the assets using the HTTP endpoint
- /
that in turn points to:
- /config
- /healthz
- /assets
- /metrics
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 livesim2as like /livesim2/cfhd/stream.mpd.
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
The query string parameter ?nowMS=... can be used in any request
to set the wall-clock time livesim2 uses as local 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.
Install Go 1.19 or later.
Optionally, create a local vendor directory to keep a local copy of
all dependencies.
Then run
> go mod tidyto fetch and install all dependencies.
To build dashfetcher and livesim2 you can use the Makefile like
> make buildto 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 ..
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/assetsThe 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.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. 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.
The dashfetcher binary can be found in as out/dashfetcher after make build.
> dashfetcher --helpwill provide a long help text that explains how to use it and will also provide an example URL to CTA-WAVE content.
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 coverageBoth 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 directory.
To get information about the available assets and other information access the server's root URL.
HTTPS and HTTP/2 are both supported. To enable TLS encryption, the two parameters
certpath and keypath must be set to point to a TLS certificate and a private
key file, respectively. It is also recommended to set the port to the default HTTPS
port 443. Automatic TLS configuration using Let's Encrypt is a future enhancement.
The URL parameters are now listed on this project's Wiki page URL-parameters.
On the livesim2 project page the status of issues and proposed new ideas are listed. Draft ideas can be changed into livesim2 issues.
This project is in need of sponsoring for further development. See the SPONSORING.md file for more information.
See LICENSE.md.