Video Transcoding: What It Is and How It Works

September 13, 2021 by
A wall of monitors playing live and on-demand video streams.
 

Transcoding allows broadcasters to convert live and on-demand streams using a streaming software or service to optimize content for each step of the workflow. This ensures greater accessibility, improved efficiencies, and a higher quality experience — while minimizing costs and complexity at the encoding stage.

Read on to learn what video transcoding is, how it works, and why it’s critical to most streaming workflows.

 

Table of Contents

 

What Is Video Transcoding?

Video transcoding involves decompressing an encoded video file, (often) altering it, and then recompressing — potentially in a different encoding format — for delivery to end users. This conversion process can take place at the media server or in a cloud-based streaming platform. By transcoding, content distributors can re-encode the data into a more common codec, transize the video into a lower resolution, or transrate the file into a lower bitrate.

 


Let’s break down that trio of Ts:

  • Video Transcoding: An umbrella term for converting a video/audio file via a multi-step process of decompressing an encoded file, possibly manipulating it in some way, and recompressing for delivery. Transrating and transizing are both subcategories of transcoding.
    • Transrating: Changing the bitrate of the decompressed file to accommodate different connection speeds. This enables more efficient storage and delivery by reducing the file size.
    • Transizing: Resizing the video frame to accommodate different screens. This allows broadcasters to adjust the resolution for delivery to various devices.
 

Why Transcode a Live Stream?

So now that we know what it is, why is video transcoding necessary? And why not just encode the stream into its final codec, resolution, and bitrate to begin with?

It has to do with the fact that the best streaming formats and configurations for first-mile contribution aren’t always the best for last-mile delivery. What’s more, creating multiple video renditions at the encoder to support adaptive bitrate (ABR) streaming is less efficient and economical than doing so using a video transcoding solution.

For instance, say you want to convert a single-bitrate Web Real-Time Communications (WebRTC) source stream into multiple output renditions that will be played back over HTTP Live Streaming (HLS). The benefits of this workflow are plenty. Sticking with WebRTC on the ingest side would enable low-latency and browser-based contribution. From there, transcoding the stream into multi-bitrate HLS would ensure large-scale delivery via a content delivery network (CDN), playback support on a number of devices, and a high-quality experience for viewers regardless of their connectivity.

Video transcoding would play an essential role in harnessing the benefits of a WebRTC to HLS workflow. And you’d likely want to use a streaming server or cloud-based streaming platform for the heavy lifting.

 

What Processes Occur During Video Transcoding?

More specifically, a live streaming platform like Wowza is critical for the following video transcoding processes:

  1. Codec conversion: WebRTC and HLS use different audio codecs, so a live transcoder would allow you to change the incoming Opus audio to a more typical format like AAC.
  2. Creating multiple output renditions: Adaptive bitrate streaming requires broadcasters to stream multiple renditions simultaneously. A video transcoding solution lets broadcasters convert the single source stream into a variety of resolution and bitrate options, enabling each viewer to play the highest-quality stream available for their device and connection speed. Even better, the stream will dynamically adjust to deliver a superior rendition if a viewer’s connectivity improves.
  3. Adding graphics: Since WebRTC enables browser-based encoding, broadcasters looking to include additional graphics in their live stream might choose to do so at the streaming server. Lower-third overlays, watermarks, and logos can all be added during video transcoding.
  4. Transmuxing: Transmuxing occurs when a media server ingests the compressed video data and repackages it into a different container format. In this example, the stream is repackaged from WebRTC to HLS. Content distributors can thereby deliver the stream to more devices using various protocols without manipulating the actual file.
 
WebRTC-to-HLS Broadcasting Workflow.
Fig 4. Typical live streaming architecture using WebRTC from the broadcaster
 

Steps one, two, and three are examples of transcoding. The fourth step, transmuxing, doesn’t necessitate decompressing and recompressing the stream. For this reason, it’s less computationally intensive than transcoding. In this case, however, transcoding the codec was an essential first step to repackaging the stream.

 

How to Transcode Live Video Streams With Wowza

We designed our live streaming software and services to make transcoding a snap. There are numerous live transcoding workflows supported in both Wowza Streaming Engine and Wowza Streaming Cloud. Below we’ve included a how-to tutorial on the architecture illustrated above: converting WebRTC to adaptive bitrate HLS.

 
 

Benefits of Video Transcoding

Video transcoding benefits everyone by keeping your content optimized for each stage of the streaming lifecycle. Here are the obstacles that transcoding eliminates for broadcasters and viewers.

On the publishing side, video transcoding resolves:

  • High costs and complexity associated with encoding multiple different resolution and bitrate options.
  • Limited playback capabilities based on the codecs, protocols, and configurations available in the encoder.
  • Inability to leverage next-generation technologies and hybrid workflows.

On the viewer side, video transcoding resolves:

  • Buffering due to low-bandwidth connections.
  • Incompatibility due to lacking format support.
  • Playback failure due to lacking device support for the resolution streamed.
  • Low-quality delivery to end-users with better connectivity and resolution capabilities than that of the stream delivered.
 

Encoding vs. Transcoding: What’s the Difference?

 

1. Encoding occurs first; transcoding occurs second.

This one might be obvious, but to belabor the point: Just as one must write a book before translating a book, a stream must be encoded before it can be transcoded.

Think of the two as the steps involved when packing for a vacation. Initially, you compress (encode) your clothing into a bag for easy transportation to wherever you’re headed. Once you arrive at your destination, you unpack, discard the items you no longer need (like that empty toothpaste tube), add trinkets gathered during your travels, and then repack your bag for the next step of your journey. This is transcoding.

 

2. Encoding is necessary; transcoding might not be.

It’s not possible to live stream a video over the internet without encoding. This process of condensing raw video into a digital format for efficient delivery across the web always occurs, even if the encoder is built into the capture device you’re broadcasting from.

Video transcoding, on the other hand, isn’t do-or-die. Plenty of workflows, such as those using WebRTC from end to end, don’t require any transcoding infrastructure. A stream can also be converted from RTMP to HLS without requiring video transcoding — but you’d miss out on adaptive bitrate streaming without transcoding the single high-bitrate RTMP stream into a multi-bitrate encoding ladder, which is a top driver for using HLS.

 

Conclusion

If every viewer had a 4K home theater plugged into high-speed internet, delivering video content would be easy. But that’s not the case. Today’s viewers are out and about, accessing streams from a variety of devices. Different screens and varying internet speeds make video transcoding and processing essential. Plus, this functionality allows you to repackage content into various formats for reliable playback on any device. Choosing a streaming platform like Wowza that offers protocol flexibility and adaptive bitrate delivery will ensure that your streams play back seamlessly across many endpoints.

 
 

Why Wowza

With more than a decade of experience powering video for 35,000 plus organizations, Wowza’s full-service platform is the gold standard for live video transcoding. Our on-the-fly technology ensures interoperability across all devices and high-quality streaming for all connection speeds — while keeping things simple at the encoder.

 

About Traci Ruether

As a Colorado-based B2B tech writer, Traci Ruether serves as Wowza's content marketing manager. Her background is in streaming and content delivery. Aside from writing, Traci enjoys cooking, gardening, and spending quality time with her kith and kin. Follow her… View more