Youtube Design - Video Publishing and Delivery

"Publishing videos on YouTube is a multifaceted procedure encompassing several stages. This discussion will address:

• Uploading videos
• Segmenting and transcoding videos
• Distributing and delivering videos via content delivery networks (CDNs)"

Video Upload - Original Storage

When a video is uploaded to YouTube, instead of being transferred as a single, large file, it is first divided into smaller, manageable segments or "blocks." This segmentation happens client-side, before the upload to YouTube's servers begins. The size of these blocks can vary, optimized for the best balance between upload speed and reliability.

Once the video blocks are uploaded, they are stored in what is referred to as the "Original storage." This storage system is designed to be highly durable and ensuring that the original, unaltered video data is preserved safely.

The original storage serves multiple purposes:

• Source for Transcoding: The stored video blocks in the original storage act as the source for the transcoding process, where videos are converted into various formats and resolutions to support different devices and bandwidth conditions.
• Backup and Recovery: In case of any issues with transcoded files or the need to create new formats in the future, the original video files serve as a backup that can be reprocessed.

The original storage system is built on a distributed storage infrastructure, capable of handling petabytes of data.

Once a video is uploaded to YouTube and stored in the original storage, it undergoes a complex process involving transcoding, storage in a transcoded format, and distribution through Content Delivery Networks (CDNs).

The Transcoding Process

Transcoding is the core of YouTube's video processing system, converting the original video file into multiple formats and resolutions. A multi-stage video transcoding process prepares uploaded videos for distribution and streaming.

Pre-Transcoding Filtering Processor

Before any video is transcoded, it undergoes a pre-processing or filtering stage. This initial step is crucial for optimizing the transcoding process and ensuring quality control.

1. Content Analysis: Videos are analyzed for various attributes, including resolution, bitrate, and format
2. Noise Reduction and Quality Enhancement: Filtering may also involve cleaning up the video and audio tracks. Noise reduction algorithms are applied to improve audio clarity.
3. Normalization: Videos are normalized to a standard format and specifications to streamline the transcoding process. This includes adjusting the video's frame rate and aspect ratio to fit within predefined parameters that accommodate a wide range of playback devices.

Encoding Processor

The core of the process, transcoding, is where the actual conversion of video files into multiple formats and resolutions takes place. This ensures that videos can be streamed over different network conditions to various devices.

1. Codec Conversion: Videos are converted from their original codecs to more efficient ones that are optimized for streaming, such as H.264. This conversion is crucial for reducing file sizes without impacting video quality.
2. Resolution and Bitrate Adaptation: Each video is transcoded into multiple resolutions and bitrates, from low-quality versions for slow mobile networks to high-definition versions for broadband connections.
3. Parallel Processing: To expedite the transcoding process, YouTube employs distributed computing, where the transcoding tasks are parallelized across multiple servers.

Upload Processor

Once videos are transcoded, they need to be delivered to viewers as efficiently as possible. This is where CDNs come into play.

• Segmentation and Storage: Transcoded video files are stored across YouTube's global network of servers and CDNs
• Edge Caching: CDNs cache these video segments close to the user's location. By serving videos from geographically distributed servers, YouTube minimizes latency and ensures smooth playback for viewers around the world.

Content Delivery Networks (IXP and ISP)

CDNs are the backbone of YouTube's video delivery system. They are distributed networks of servers that cache content like video files closer to where users are located. When a user clicks on a video, the request is routed to the nearest CDN server holding the cached content, significantly reducing the delivery time

Internet Exchange Points (IXPs)

IXPs are physical infrastructure through which Internet Service Providers (ISPs) exchange internet traffic between their networks. YouTube leverages IXPs to efficiently distribute its content across different ISPs, enhancing the speed and reliability of video streaming.

• Reduces Latency and Costs: By facilitating the direct exchange of traffic between YouTube's network and ISPs at IXPs, the distance data travels is significantly reduced. This not only improves speed and reduces latency for the end-user but also lowers the cost of data transit for YouTube and the ISPs.
• Enhances Bandwidth Capacity: IXPs provide YouTube with the bandwidth capacity needed to handle massive volumes of data, ensuring that high-definition video content can be streamed smoothly to users without buffering, even during peak times.

Internet Service Providers (ISPs) and ISP Caches

ISPs connect users to the internet and play a crucial role in the final delivery of YouTube videos to viewers. They provide:

• Direct Peering: YouTube often establishes direct peering relationships with ISPs, where YouTube's servers are directly connected to the ISP's network. This allows for more efficient routing of content and reduced congestion, enhancing the user experience.