CDN Video Streaming & Media Delivery 4 — Questions and Answers
Question 1: In server-side ad insertion (SSAI), what problem does it solve compared to client-side ad insertion?
- Eliminates ad blockers by stitching ads into the video stream at the server (Correct answer)
- Reduces origin storage costs by compressing ad assets
- Allows viewers to choose their own ad content
- Improves DRM security for premium content
Correct answer: Eliminates ad blockers by stitching ads into the video stream at the server
SSAI stitches advertisements directly into the video stream server-side, making the ads indistinguishable from content and immune to client-side ad blockers.
Question 2: What is the purpose of a CDN 'token authentication' mechanism for video content?
- Ensures only authorized users with valid signed URLs can access protected video segments (Correct answer)
- Speeds up segment delivery by pre-authenticating edge nodes
- Compresses video tokens to reduce manifest file size
- Enables multi-CDN failover without re-authentication
Correct answer: Ensures only authorized users with valid signed URLs can access protected video segments
Token authentication uses cryptographically signed URLs or cookies to ensure only authenticated users can retrieve protected video content from the CDN.
Question 3: Which metric best measures viewer-perceived video quality during adaptive bitrate streaming?
- Mean Opinion Score (MOS) or Video Multimethod Assessment Fusion (VMAF) (Correct answer)
- Total bytes delivered per session
- Number of HTTP 206 partial content responses
- Average CDN edge node CPU utilization
Correct answer: Mean Opinion Score (MOS) or Video Multimethod Assessment Fusion (VMAF)
VMAF and MOS are perceptual quality metrics that correlate with how viewers subjectively experience video quality, unlike purely technical throughput metrics.
Question 4: A CDN delivers a 2-hour VOD film. Which caching strategy is most appropriate for the video segments?
- Long TTL with immutable cache headers since VOD segments never change (Correct answer)
- Short TTL of 30 seconds to ensure freshness
- No caching; always fetch from origin
- Cache only the first 10 minutes of the film
Correct answer: Long TTL with immutable cache headers since VOD segments never change
VOD segments are static and never change, so immutable cache headers with long TTLs maximize cache efficiency and minimize origin load.
Question 5: What is 'chunked transfer encoding' and why is it relevant to live video streaming?
- Sends data in chunks without knowing the total content length, enabling streaming of live segments as they are generated (Correct answer)
- Splits large video files into 10MB chunks for parallel download
- Encrypts video segments in fixed-size blocks for DRM
- Divides CDN bandwidth among concurrent viewers equally
Correct answer: Sends data in chunks without knowing the total content length, enabling streaming of live segments as they are generated
Chunked transfer encoding allows HTTP to send data in pieces without a predetermined content length, which is essential for delivering live video as it is encoded.
Question 6: What is the function of a 'media manifest' in adaptive streaming?
- Describes available quality levels and provides URLs or templates for video segments (Correct answer)
- Stores the actual encoded video data for playback
- Contains viewer authentication credentials for DRM
- Defines CDN routing rules for segment requests
Correct answer: Describes available quality levels and provides URLs or templates for video segments
A media manifest (like HLS .m3u8 or DASH MPD) is a metadata file that lists available bitrate renditions and tells the player where to fetch each segment.
Question 7: During a major live event, a CDN operator observes a sudden 10x spike in concurrent viewers. Which CDN feature automatically handles this traffic surge?
- Elastic scaling with request coalescing to prevent origin overload (Correct answer)
- Static IP allocation for all edge nodes
- Reducing segment duration to 2 seconds
- Disabling DRM verification for faster delivery
Correct answer: Elastic scaling with request coalescing to prevent origin overload
Request coalescing (or request collapsing) on elastic CDN infrastructure combines simultaneous cache-miss requests for the same segment into a single origin fetch, protecting origin during traffic spikes.
CDN Video Streaming & Media Delivery 4
In server-side ad insertion (SSAI), what problem does it solve compared to client-side ad insertion?