What is Video Transcoding
It refers to the process of converting a video file from one format or codec to another. This allows video files captured or encoded in one format to be played back on devices that support different formats. Transcoding is necessary because video formats have different technical specifications for things like resolution, frame rate, audio channels and compression standards.
Need for Video Transcoding
The need for transcoding arises because videos today need to be consumed across a wide variety of platforms like smartphones, tablets, desktops and streaming devices. However, not all devices or platforms support the same video formats. While a high-resolution movie may play fine on a high-end desktop, the same file may be too large for a mobile device with limited processing power and storage. Transcoding allows video content distributors to create optimized versions of a video tailored for specific devices or networks.
Some key reasons why transcoding is required include:
- Device and Platform compatibility: As mentioned earlier, different devices have varying support for video formats. Transcoding ensures the video can play on the target device.
- File size optimization: Transcoding to lower resolutions and bitrates helps reduce file sizes, important for streaming over cellular networks or for devices with limited space.
- Encoding optimizations: Transcoding allows re-encoding videos using optimal encoder settings, codecs and profiles best suited for the target environment.
- DRM restrictions: Video Transcoding may need to be converted to formats that support Digital Rights Management (DRM) for distribution through licensing platforms.
- Subtitle/Closed caption embedding: Non-burned subtitle/caption streams can be burned into the video during transcoding.
Transcoding Workflow
A typical video transcoding workflow would involve the following basic steps:
1. Import and Analysis: The source video file is imported into the transcoding system which then analyses key attributes like resolution, frame rate, audio/subtitle streams etc.
2. Profile Mapping: The analyzed data is mapped to pre-defined transcoding profiles configured for various target device classes or bitrate tiers.
3. Transcoding: The source file is transcoded to the appropriate target format(s), resolutions and encoding parameters as per the matched profile using CPU/GPU transcoding.
4. Optimizations: Additional optimizations may be applied like deinterlacing, denoising, ad insertion etc.
5. Quality Check: Random transcoded clips can be checked for quality issues using automated or manual review.
6. Delivery/Distribution: The transcoded files are delivered to various streaming servers, packaged for OTT/VOD platforms or downloaded directly for local playback.
Transcoding Formats and Codecs
Some common formats generated during transcoding include:
- MP4: A popular wrapper format generated at lower resolutions for platforms like iOS, Android, Roku etc. H.264 video with AAC audio is common.
- MPEG-2 Program Stream (M2PS): Used for distribution to set-top boxes and cable/satellite systems.
- Flash Video (FLV/F4V): Used for progressive download and streaming delivery to desktop browsers.
- Microsoft Smooth Streaming (MSS): An adaptive bitrate format optimized for Silverlight/HTML5 delivery.
- HLS: A standard HTTP Live Streaming format for OTT on mobile/desktop with H.264/AAC.
- DASH: An ISO-standard dynamic adaptive format popular for premium OTT with H.264/AAC or HEVC/AAC.
Popular codecs used include H.264, H.265/HEVC for video compression and AAC, MP3 for audio. Selecting the right codecs and container depends on the target audience and delivery network.
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