CDN Video Streaming & Media Delivery 2 — Questions and Answers
Question 1: Which CDN technique reduces startup latency for live video streams by pre-positioning the first few segments at edge nodes before viewers request them?
- Segment prefetching (Correct answer)
- Manifest caching
- Origin shielding
- Token authentication
Correct answer: Segment prefetching
Segment prefetching pushes the initial video segments to edge nodes proactively, reducing the time-to-first-frame for live streams.
Question 2: In HLS streaming, what is the purpose of the EXT-X-DISCONTINUITY tag in a playlist?
- Marks a break in stream continuity such as an ad insertion point (Correct answer)
- Signals the end of the playlist
- Defines the target segment duration
- Indicates an encrypted segment
Correct answer: Marks a break in stream continuity such as an ad insertion point
EXT-X-DISCONTINUITY signals that there is a break in continuity between the preceding and following media segments, commonly used at ad insertion boundaries.
Question 3: A CDN reports a high 'rebuffering ratio' for video streams. Which metric most directly indicates the severity of this problem?
- Percentage of total playback time spent buffering (Correct answer)
- Total number of unique viewers
- Average segment size in kilobytes
- Cache hit ratio for manifests
Correct answer: Percentage of total playback time spent buffering
The rebuffering ratio — buffering time divided by total playback time — directly measures how often viewers experience stalls relative to watch time.
Question 4: Which protocol allows CDN edges to push video segments to viewers over a single persistent connection without repeated HTTP polling?
- WebSocket
- HTTP/2 Server Push (Correct answer)
- RTMP
- MPEG-DASH over HTTP/1.1
Correct answer: HTTP/2 Server Push
HTTP/2 Server Push enables the server to proactively send resources to clients over the same connection before they are explicitly requested.
Question 5: What is the role of a 'packaging service' in a video CDN pipeline?
- Converts encoded video into adaptive streaming formats like HLS and DASH (Correct answer)
- Compresses raw video files using H.264
- Authenticates viewer tokens before delivery
- Monitors cache fill rates at edge nodes
Correct answer: Converts encoded video into adaptive streaming formats like HLS and DASH
A packaging service takes encoded video and wraps it into adaptive streaming manifests and segment formats (HLS, DASH) suitable for CDN delivery.
Question 6: When a viewer switches from a high-bitrate to a low-bitrate rendition mid-stream, which ABR behavior is occurring?
- Downshift or quality downgrade (Correct answer)
- Segment revalidation
- Manifest refresh
- Origin failover
Correct answer: Downshift or quality downgrade
An ABR downshift occurs when the player detects insufficient bandwidth and switches to a lower-bitrate rendition to prevent rebuffering.
Question 7: Which CDN configuration setting controls how long a video segment is stored at an edge node before it is considered stale?
- Cache TTL (Time-To-Live) (Correct answer)
- Segment duration
- Manifest version
- Bitrate ladder step
Correct answer: Cache TTL (Time-To-Live)
Cache TTL defines how long cached content remains valid at the edge before the CDN must revalidate or re-fetch it from origin.
CDN Video Streaming & Media Delivery 2
Which CDN technique reduces startup latency for live video streams by pre-positioning the first few segments at edge nodes before viewers request them?