CDN Video Streaming & Media Delivery 3 — Questions and Answers
Question 1: In MPEG-DASH, what does the 'MPD' file contain?
- Media Presentation Description with all available representations and segment URLs (Correct answer)
- Master playlist with encryption keys
- Real-time viewer analytics data
- CDN node health status
Correct answer: Media Presentation Description with all available representations and segment URLs
The MPD (Media Presentation Description) is DASH's manifest file that describes all available quality representations, segment templates, and timing information.
Question 2: A sports broadcaster wants to minimize live stream latency to under 3 seconds. Which technology stack best achieves this?
- Low-Latency HLS (LL-HLS) with partial segments (Correct answer)
- Standard HLS with 10-second segments
- Progressive download over HTTP/1.1
- RTMP to Flash player
Correct answer: Low-Latency HLS (LL-HLS) with partial segments
LL-HLS uses partial segments and blocking playlist reloads to achieve sub-3-second latency while maintaining CDN scalability.
Question 3: What is 'just-in-time packaging' (JIT) in the context of CDN video delivery?
- Segments are transcoded and packaged at the edge only when a viewer requests them (Correct answer)
- Video is pre-packaged 24 hours before broadcast
- Manifests are cached permanently at origin
- DRM keys are generated at viewer device startup
Correct answer: Segments are transcoded and packaged at the edge only when a viewer requests them
JIT packaging generates adaptive streaming segments on-demand at the CDN edge or origin, eliminating the need to pre-package every format and bitrate.
Question 4: Which HTTP header is primarily used to instruct CDN edges on whether to cache a video segment and for how long?
- Cache-Control (Correct answer)
- Content-Encoding
- X-Forwarded-For
- Accept-Ranges
Correct answer: Cache-Control
The Cache-Control header with directives like max-age tells CDN edge nodes how to cache responses and for how long.
Question 5: A video platform notices that 4K stream requests are frequently missing CDN cache and hitting origin. What is the most likely cause?
- High bitrate variants have low request frequency, reducing cache hit rates (Correct answer)
- 4K streams use a different transport protocol that bypasses CDN
- Origin servers block 4K content from being cached
- CDN nodes do not support files larger than 1 GB
Correct answer: High bitrate variants have low request frequency, reducing cache hit rates
4K content is less popular than lower resolutions, so its segments are requested less frequently, leading to cache evictions and more origin fetches.
Question 6: What does the term 'glass-to-glass latency' measure in live video streaming?
- Total delay from camera capture to display on the viewer's screen (Correct answer)
- Time for a CDN request to travel to origin and back
- Duration of a single video segment
- Delay introduced by DRM license acquisition
Correct answer: Total delay from camera capture to display on the viewer's screen
Glass-to-glass latency measures the end-to-end delay from the moment a camera captures a frame to when it appears on the viewer's display.
Question 7: Which encoding concept defines the set of bitrate and resolution options offered to an ABR player?
- Bitrate ladder (Correct answer)
- Segment manifest
- DRM profile
- Edge routing table
Correct answer: Bitrate ladder
A bitrate ladder is the predefined set of encoding profiles (bitrate + resolution pairs) from which an ABR player selects based on network conditions.
CDN Video Streaming & Media Delivery 3
In MPEG-DASH, what does the 'MPD' file contain?