Streaming video requires the working of various technologies in unison. One aspect of this process involves knowing the various streaming protocols responsible for delivering both live streams and VoD to your viewers. As more and more streaming solution providers, broadcasters, and CDN providers prepare for a future filled with the widespread use of live streaming, the need for exploring more efficient protocols as an individual content producer has never been greater. This blog would focus on comparing SRT, an emerging streaming protocol with HLS and MPEG-DASH– the two most popular streaming standards.
Initially developed by Haivision Systems Inc., SRT is an open-source video transport protocol and technology stack built for optimizing streaming performance across unreliable networks with secure streams. Based on UDP, SRT makes it possible to transfer any data type, however, it is particularly optimized for audio/video streaming.
You see, what happens while streaming is, video/audio packets sent between two points experience a host of transport obstacles like bandwidth fluctuations and packet loss. As a result, video quality at the endpoint gets delivered at a lower quality than what it originally was. The goal of SRT implementation is to solve that issue.
By adapting to real-time network conditions, SRT optimizes video transport from one end to the other over unpredictable networks and minimizes packet loss, leading to a better QoE. It delivers high-quality video and audio with low latency. Not only that, with easy firewall traversal, SRT makes it possible to bring the best quality live video over the worst networks.
Since SRT is still in the early stages of development, full-fledged implementation is still a work in progress. Most of the major live streaming platforms haven’t yet adopted SRT into their systems, which means that they can’t be used as endpoints. However, since it is open source and royalty-free, we expect more industry developers to integrate SRT into their systems in the coming months.
SRT (Secure Reliable Transport) is an open-source video streaming protocol that is specifically designed for secure and reliable transmission of video over unreliable networks, such as the internet. SRT has gained significant popularity in the video streaming industry due to its low-latency, error correction, and congestion control features. Here are some key applications of SRT in video streaming:
SRT (Secure Reliable Transport) is an open-source streaming protocol designed for transmitting high-quality video, audio, and data over unreliable or unpredictable networks, such as the internet. It was developed to address the challenges of streaming media over long-distance and unreliable connections, offering low latency and high reliability. SRT is widely used in various industries, including broadcasting, video conferencing, and live streaming applications. Here’s an overview of how SRT works:
The SRT protocol uses the UDP (User Datagram Protocol) as its transport layer by default, but it can also work over TCP (Transmission Control Protocol) as an option. When a connection is established, both the sender and receiver negotiate the parameters for the transmission, such as the desired latency, bit rate, and other network-specific settings.
SRT supports encryption and authentication to ensure data security during transmission. It utilizes the Secure Sockets Layer (SSL) protocol to encrypt data before sending it over the network, protecting it from potential eavesdropping and tampering.
One of the key features of SRT is its ability to handle packet loss and network jitter effectively. It employs a combination of error correction techniques, forward error correction (FEC), and retransmission to recover lost packets and maintain stream reliability. This ensures that even in challenging network conditions, the media stream remains smooth and continuous.
SRT is designed to achieve low latency streaming, making it suitable for real-time applications. The protocol allows users to control the latency by adjusting settings like buffer size, transmission window, and retransmission delay. This flexibility enables users to optimize the trade-off between latency and reliability based on their specific use case.
SRT dynamically adjusts the bit rate of the media stream based on the available network bandwidth. It can adapt to fluctuating network conditions, allowing the stream to continue even in situations with varying levels of available bandwidth.
SRT incorporates NAT (Network Address Translation) traversal techniques, making it easier to establish connections between devices behind firewalls and routers. This feature simplifies the process of setting up and managing streams across different network topologies.
SRT provides valuable statistics and feedback to both the sender and receiver, allowing them to monitor the health of the stream and adjust as needed. This helps diagnose issues and optimize the streaming experience.
Developed by Apple, HLS is a protocol for streaming live video content over the internet. HLS is short for HTTP Live Streaming. HLS is an adaptive, HTTP-based streaming protocol that sends video and audio content over the network in small, TCP-based media chunks that get reassembled during playback.
Initially, HLS was supported only by iOS. However, HLS has now become a proprietary format, and almost every device supports it. That means a stream delivered via HLS will guarantee playback on the majority of devices — thereby expanding your audience. All Google Chrome browsers, as well as Android, Linux, Microsoft, and macOS devices can play streams delivered using HLS.
As the name suggests, HLS delivers video content via standard HTTP web servers. This means that you don’t have to integrate any special infrastructure to deliver HLS content.
HTTP Live Streaming (HLS) is a popular video streaming protocol developed by Apple. It has become widely adopted and is used for various applications in video streaming due to its adaptive streaming capabilities and compatibility with multiple devices and platforms. Here are some key applications of HLS in video streaming:
HTTP Live Streaming (HLS) is a popular streaming protocol developed by Apple for delivering live and on-demand multimedia content over the internet. It is widely used for streaming video and audio content to various devices, including smartphones, tablets, computers, and smart TVs. HLS works by breaking the content into small, manageable segments and using HTTP to deliver these segments to the client devices. Here’s an overview of how HLS streaming works:
The media content (video/audio) is first encoded into multiple versions at different bit rates and resolutions to accommodate various network conditions and device capabilities. These different versions are known as “variants” or “renditions.” Each variant is divided into smaller segments, typically lasting 2 to 10 seconds, but this duration can be adjusted based on the use case.
The server creates a manifest file, known as the “m3u8” playlist, which contains references to the available variants and their corresponding segment URLs. The manifest file is a plain text file in the HLS format and serves as the entry point for the client to access the content. It provides information about the available bit rates, resolutions, and segment URLs for each variant.
When a client (e.g., a web browser or media player) requests to play a stream, it first fetches the manifest file over HTTP. The manifest file contains the URLs to the media segments for each variant, allowing the client to choose the most suitable variant based on factors like network bandwidth and device capabilities.
HLS utilizes adaptive bitrate streaming to ensure smooth playback regardless of varying network conditions. The client selects an initial variant to play based on its capabilities and network conditions. As the playback progresses, the client continuously monitors the network and switches to a different variant if the available bandwidth changes. This way, the client can adjust the video quality in real-time, providing a better viewing experience.
Once the client selects a variant, it starts downloading the media segments in sequence over HTTP. Each segment is a standalone file, so even if a connection is interrupted, the client can resume playback easily. As segments are fetched, they are played in order, resulting in a continuous playback experience.
HLS is designed to support continuous streaming for both live and on-demand content. For live streaming, the media segments are generated in real-time and appended to the manifest file. This allows viewers to join the live stream at any time and receive the most recent segments.
MPEG-DASH is the latest and by far, the best competitor of HLS. Created by Moving Picture Experts Group between 2009 and 2012, it uses standard HTTP web servers like HLS. DASH is short for Dynamic Adaptive Streaming over HTTP that means that like HLS, it’s an adaptive bitrate protocol.
MPEG-DASH is codec and resolution agnostic, which means MPEG-DASH can stream video and audio of any format (H.264, H.265, AAC, etc.) and supports resolutions up to 4K. Otherwise, MPEG-DASH functions much the same as HLS. to know more about HLS & MPEG-DASH, go through our blog on HLS vs MPEG DASH: Which Streaming Protocol Should You Choose?
MPEG-DASH (Dynamic Adaptive Streaming over HTTP) is a streaming protocol that enables efficient video delivery over the internet. It works by dividing the video content into small segments and dynamically adapting the quality of the stream based on the user’s network conditions and device capabilities. Here’s a step-by-step explanation of how MPEG-DASH works:
The video content is encoded into various bitrate representations or quality levels, typically using H.264 or H.265 video codecs and AAC audio. Each representation is divided into small segments, usually 2-10 seconds in duration.
The server generates a Media Presentation Description (MPD) file, which is an XML manifest that contains information about the available representations, segment URLs, and other metadata required for playback.
The client, such as a web browser or streaming application, initiates a streaming session by sending an HTTP request to the server, asking for the MPD file.
Upon receiving the MPD, the client parses it and identifies the available Adaptation Sets, each representing a set of representations with different qualities (bitrates and resolutions). The client then selects the appropriate representation based on factors like available bandwidth, device capabilities, and user preferences.
The client begins downloading video segments from the server using HTTP GET requests. Initially, the client may download segments of lower quality to start playback quickly and to ensure a smooth start.
As the video playback progresses, the client continuously monitors the network conditions. If the network bandwidth improves, the client may request higher-quality segments to enhance the viewing experience. Conversely, if the network conditions deteriorate, the client may request lower-quality segments to avoid buffering.
The client can smoothly switch between representations during playback. This process is usually achieved by buffering a few segments ahead and behind the current playback point to ensure a seamless transition.
The streaming session continues until the user stops playback or exits the application. The client will stop requesting segments, and the streaming session is terminated.
Streaming protocols perform differently in different areas, and one should carefully analyze them before narrowing down upon one. Some of the parameters that decide the performance of streaming protocols are as follows :
Prioritizing the above parameters helps you to narrow down on what’s best for you.
While SRT is a great bet for first-mile contribution, both HLS and DASH win hands down when it comes to playback. Better playback compatibility leads to a wider outreach, which leads to more engagement.
If latency or poor network conditions aren’t an issue, then HLS or MPEG-DASH beats out SRT. Both DASH and HLS are ABR enabled which helps in delivering the best possible video quality to viewers with different network conditions. Also, DASH and HLS are more straightforward to set up than SRT.
If you compare DASH and HLS, the weighing scale of compatibility would tip towards HLS. Here’s why- iOS users represent 25.26% in the global mobile operating system market share. Most of these users can’t play MPEG-DASH video streams unless they use third-party browsers.
Muvi supports RTMP and HLS feeds for your Live Streaming service. You just have to enter your live feed URL in the backend and Muvi’s Online Video Player will embed the feed for immediate playback to end-users.
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Which is More Widely Supported?
HLS and MPEG-DASH were more established and widely supported, while SRT was gaining traction and seeing increased adoption in specific use cases.
Which Offers Higher-Quality Streaming?
All three protocols (SRT, HLS, and MPEG-DASH) can offer high-quality streaming experiences when implemented appropriately and with the right video encoding settings. The adaptive bitrate streaming capabilities of HLS and MPEG-DASH contribute to smoother playback by adjusting the quality to match network conditions.
Which Protocol is More Reliable?
SRT is designed explicitly to address challenges related to unreliable networks and is likely the most reliable choice among the three protocols. It provides error recovery, retransmission, and other mechanisms to maintain a stable video stream even under adverse network conditions. HLS and MPEG-DASH, on the other hand, are more focused on adaptive bitrate streaming and are generally reliable in typical network scenarios, but they may not offer the same level of resilience as SRT for particularly challenging network conditions.
Which Protocol Should You Use?
The best protocol for your use case depends on factors such as the type of content you are delivering, the target audience and their devices, the level of reliability required, and the network conditions you expect to encounter. It’s essential to assess your specific streaming needs and conduct thorough testing to determine which protocol aligns best with your requirements.
Which is better: low latency HLS or DASH?
Both low latency HLS and low latency DASH have their advantages and are capable of reducing latency for live streaming. The decision on which is “better” depends on your specific use case, platform support requirements, existing infrastructure, and implementation preferences. Evaluate your streaming needs and conduct tests to determine which protocol aligns best with your desired latency and viewing experience.
Written by: Sreejata Basu
Sreejata is the Manager for Muvi’s Content Marketing unit. She is a passionate writer with a background in English Literature and music. By week Sreejata spends her time in the corporate world of Muvi, but on weekends she likes to take short hiking trips, watch movies and read interesting travelogues.
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