SRT to WHEP

This application ingests one MPEG-TS over SRT stream and outputs to WebRTC recvonly clients using WHEP as signaling protocol. Example of use cases:

• Browser based confidence monitor of an incoming stream
• Program or preview output monitor in a browser or tablet

Supports SRT streams in caller and listener mode. Runs on MacOS and Ubuntu.

Design Principles

When conceiving this project, we made deliberate design choices to shape its functionality and behavior in alignment with our vision:

• No Video Transcoding: We have intentionally refrained from implementing video transcoding within this component. This decision stems from the desire to maintain the integrity of the original video stream. This approach caters to use cases like confidence monitoring or preview. If you wish to transcode video anyway, here is an example to do that.
• Server-Side Initiation Mode: Our project does not currently support the client-side initiation mode of WebRTC-HTTP Egress Protocol (WHEP). Instead, we have adopted a server-side initiation approach. In this mode, the server provides the SDP offer, as it possesses knowledge of the available streams.
• Focus on SDP Offer/Answer Exchange: Our server's primary focus is on the exchange of SDP (Session Description Protocol) offers and answers. While WebRTC typically involves ICE (Interactive Connectivity Establishment) negotiation for establishing peer-to-peer connections, we have opted not to include ICE negotiation within the scope of our project at this time. Our emphasis remains on the effective exchange of SDP-related information.

Compliance Table

Here we have a list of supported production software.

Getting Started

It is suggested that

• Mac Users: Follow our comprehensive build instructions and use Chrome for streaming.
• Ubuntu Users: Either build the program from source or use Docker for running. Both methods are supported.

Some useful commands can be found here.

Install

cargo install srt_whep

# recommended for pretty log viewer (optional)
cargo install bunyan

Generate an SRT test source for example using our testsrc Docker container:

docker run --rm -p 1234:1234/udp eyevinntechnology/testsrc

An SRT stream (in listener mode) is then available at srt://127.0.0.1:1234. Then run the srt-whep application:

srt-whep -i 127.0.0.1:1234 -o 127.0.0.1:8888 -p 8000 -s caller | bunyan

It will connect to the SRT test stream in caller mode as the generated SRT stream is in listener mode.

WHEP endpoint is available at http://localhost:8000/channel. You can then play it for example using the WHEP Player. Possible issues are discussed in Issues.

If you don't have Rust install you can use the Docker Container image published on Docker Hub:

docker run --rm --network host eyevinntechnology/srt-whep \
  -i 127.0.0.1:1234 \
  -o 0.0.0.0:8888 \
  -p 8000 -s caller

Note that the container needs to run in host-mode (supported only on Linux).

Build from Source

OSX

Requirements:

• XCode command line tools installed
• GStreamer binaries from GStreamer's website installed
• Rust and cargo installed

Make sure you have the following env variables defined:

export PATH=$PATH:/Library/Frameworks/GStreamer.framework/Versions/Current/bin
export PKG_CONFIG_PATH=/Library/Frameworks/GStreamer.framework/Versions/Current/lib/pkgconfig
export GST_PLUGIN_PATH=/Library/Frameworks/GStreamer.framework/Versions/Current/lib
export DYLD_FALLBACK_LIBRARY_PATH=$GST_PLUGIN_PATH

Build with Cargo

cargo check
cargo install bunyan # Optional, for pretty printing of logs
cargo build --release

The binary is then available at ./target/release/srt-whep. See below for how to run it.

Debian (bullseye / bookworm)

Requirements:

• Rust and cargo installed

Install GStreamer build dependencies.

apt-get update
apt-get -y install build-essential \
  curl \
  pkg-config \
  libssl-dev \
  libunwind-dev \
  libgstreamer1.0-dev \
  libgstreamer-plugins-base1.0-dev \
  libgstreamer-plugins-bad1.0-dev \
  gstreamer1.0-plugins-base \
  gstreamer1.0-plugins-good \
  gstreamer1.0-plugins-bad \
  gstreamer1.0-plugins-ugly \
  gstreamer1.0-libav \
  gstreamer1.0-tools \
  gstreamer1.0-x \
  gstreamer1.0-alsa \
  gstreamer1.0-gl \
  gstreamer1.0-gtk3 \
  gstreamer1.0-qt5 \
  gstreamer1.0-pulseaudio \
  gstreamer1.0-nice

Build with Cargo

cargo check
cargo install bunyan # Optional, for pretty printing of logs
cargo build --release

The binary is then available at ./target/release/srt-whep. See below for how to run it.

Docker Container

Build container (uses multi-stage builds):

docker build -t srt-whep:dev .

Container must be running in host-mode (only works on Linux hosts, and is not supported on Docker Desktop for Mac, Docker Desktop for Windows)

docker run --rm --network host srt-whep:dev \
  -i <SRT_SOURCE_IP>:<SRT_SOURCE_PORT> \
  -o 0.0.0.0:8888 \
  -p 8000 -s caller

Usage

To ingest an SRT stream with address srt://127.0.0.1:1234 in listener mode and expose WHEP endpoint on port 8000 run the application with this command.

cargo run --release -- -i 127.0.0.1:1234 -o 127.0.0.1:8888 -p 8000 -s caller | bunyan

This will also make a pass-through of the SRT stream on srt://127.0.0.1:8888 in listener mode. To watch the pass-through stream in ffplay, VLC or GStreamer you run:

ffplay srt://127.0.0.1:8888
# or
gst-launch-1.0 playbin uri="srt://127.0.0.1:8888"

WHEP endpoint is available then at http://localhost:8000/channel. You can then play it for example using the WHEP Player.

If the SRT stream to ingest is in caller mode you run the application with this command.

cargo run --release -- -i 127.0.0.1:1234 -o 127.0.0.1:8888 -p 8000 -s listener | bunyan

This also expects the SRT address 127.0.0.1:8888 to be running in caller mode.

Tips for Successful Streaming

When working with SRT streams, there are several important considerations that can affect the success of your streaming experience:

1. Stream Generation and Playback Tools:

• Different tools, such as FFMpeg, GStreamer, FFPlay, and VLC, can be used to generate and play SRT streams. We've tested our program with these tools, so you can choose the one that suits your needs.
• Be aware of the mode option in the SRT stream configuration, which can be set as caller, listener, or rendezvous. This option determines the behavior of the stream, and it needs to be configured correctly for successful streaming.

2. Bitrate Parameter in FFMpeg Streams:

• When generating streams using FFMpeg, it's essential to specify the Bitrate parameter. Failing to do so might result in VLC/GStreamer being unable to play the stream.

3. Video Codecs and Profiles:

• WebRTC connection failures can often be attributed to incompatible video codecs. While we strive to support both H.264 (AVC) and H.265 (HEVC) streams, it's important to note that most mainstream browsers only support AVC for WebRTC.
• Safari, which is the only browser supporting H.265, has its own RTP payload format and custom video profile requirements, different from the standard (RFC 7798). So it does not work directly out of box. There is a PR available for fixing this H265 packetization issue in WebKit project but no one is viewing it for the moment.
• Based on the discussion, it seems rather challenging to support H.265 / HEVC right now.

4. Codecs and Profiles Compatibility:

• Video profiles, such as Baseline, Main, and High for H.264, play a crucial role in stream compatibility. While Chrome supports all profiles, Safari only accepts the Baseline profile. For further details, please refer to this table.

5. SRT Stream Latency:

• SRT streams can be configured to have different latencies. For example, if you're using GStreamer to generate SRT streams, you can set the latency parameter of srtsink or srtsrc to fit your need. For example, latency=200 sets the latency to 200ms, which is appropriate for most use cases.
• Our tool adds a minimun latency to the stream by default. If you want to measure the end-to-end latency, you can try to generate a stream using OBS with a clock overlay (which adds a very low latency). Then you can compare the clock in the stream with the built-in clock from our WHEP player. The end-to-end latency should be around 300~500 ms.

Discussion and Issues

All relevant discussions are tracked in issues. Please feel free to open a new issue if you have any questions.

• We have a set of known limitations recorded here. You might want to check it out if running into an issue.
• If you doubt a plugin is missing in gstreamer you can check it using gst-inspect-1.0 <plugin>. For example, gst-inspect-1.0 srtsink.
• To get more verbose logging you can set the GST_DEBUG environment variable to 2. For example, run in terminal: export GST_DEBUG=2

License (Apache-2.0)

Copyright 2023 Eyevinn Technology AB

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Support

Join our community on Slack where you can post any questions regarding any of our open source projects. Eyevinn's consulting business can also offer you:

• Further development of this component
• Customization and integration of this component into your platform
• Support and maintenance agreement

Contact sales@eyevinn.se if you are interested.

About Eyevinn Technology

Eyevinn Technology is an independent consultant firm specialized in video and streaming. Independent in a way that we are not commercially tied to any platform or technology vendor.

At Eyevinn, every software developer consultant has a dedicated budget reserved for open source development and contribution to the open source community. This give us room for innovation, team building and personal competence development. And also gives us as a company a way to contribute back to the open source community.

Want to know more about Eyevinn and how it is to work here. Contact us at work@eyevinn.se!