In the event you’re thinking about streaming media, you probably fall into one in all two camps: Either you already know something about transcoding, or you’re wondering why you keep hearing about it. If you happen to aren’t sure you want it, bear with me for a couple of paragraphs. I’ll explain what transcoding is (and isn’t), and why it is perhaps critical in your streaming success — particularly if you want to deliver adaptive streams to any device.
So, What Is Transcoding?
First, the word transcoding is commonly used as an umbrella term that covers a number of digital media tasks:
Transcoding, at a high level, is taking already-compressed (or encoded) content material; decompressing (decoding) it; after which somehow altering and recompressing it. For example, you may change the audio and/or video format (codec) from one to a different, reminiscent of converting from an MPEG2 supply (commonly used in broadcast television) to H.264 video and AAC audio (the most well-liked codecs for streaming). Different fundamental tasks could embody adding watermarks, logos, or other graphics to your video.
Transrating refers specifically to changing bitrates, corresponding to taking a 4K video enter stream at 13 Mbps and changing it into one or more lower-bitrate streams (also known as renditions): HD at 6Mbps, or other renditions at 3 Mbps, 1.eight Mbps, 1 Mbps, 600 kbps, etc.
Transsizing refers specifically to resizing the video frame; say, from a decision of 3840×2160 (4K UHD) down to 1920×1080 (1080p) or 1280×720 (720p).
So, if you say “transcoding,” you might be referring to any mixture of the above tasks — and typically are. Video conversion is computationally intensive, so transcoding usually requires more powerful hardware resources, including faster CPUs or graphics acceleration capabilities.
What Transcoding Is Not
Transcoding should not be confused with transmuxing, which will also be referred to as repackaging, packetizing or rewrapping. Transmuxing is once you take compressed audio and video and — without changing the actual audio or video content — (re)package it into completely different delivery formats.
For example, you might need H.264/AAC content material, and by changing the container it’s packaged in, you’ll be able to deliver it as HTTP Live Streaming (HLS), Clean Streaming, HTTP Dynamic Streaming (HDS) or Dynamic Adaptive Streaming over HTTP (DASH). The computational overhead for transmuxing is way smaller than for transcoding.
When Is Transcoding Critical?
Merely put: Transcoding is critical whenever you need your content to reach more end users.
For instance, let’s say you need to do a live broadcast using a camera and encoder. You is perhaps compressing your content material with a RTMP encoder, and select the H.264 video codec at 1080p.
This must be delivered to online viewers. But should you attempt to stream it directly, you will have a couple of problems. First, viewers without adequate bandwidth aren’t going to be able to view the stream. Their players will be buffering always as they wait for packets of that 1080p video to arrive. Secondly, the RTMP protocol is not widely supported for playback. Apple’s HLS is way more widely used. Without transcoding and transmuxing the video, you will exclude almost anyone with slower data speeds, tablets, mobile phones, and related TV devices.
Utilizing a transcoding software or service, you may simultaneously create a set of time-aligned video streams, each with a special bitrate and frame size, while changing the codecs and protocols to reach additional viewers. This set of internet-pleasant streams can then be packaged into several adaptive streaming codecs (e.g., HLS), permitting playback on nearly any screen on the planet.
One other widespread instance is broadcasting live streams utilizing an IP camera, as would be the case with surveillance cameras and traffic cams. Again, to achieve the largest number of viewers with the best possible quality allowed by their bandwidth and gadgets, you’d need to support adaptive streaming. You’d deliver one HD H.264/AAC stream to your transcoder (typically positioned on a server image in the cloud), which in flip would create multiple H.264/AAC renditions at totally different bitrates and resolutions. Then you definately’d have your media server (which might be the identical server as your transcoder) package those renditions into one or more adaptive streaming formats earlier than delivering them to finish users.
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