# Resolve CDN ad break timing and synchronization issues for MediaTailor
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AWS Elemental MediaTailor content delivery network (CDN) ad break timing must be precisely synchronized with content markers. If ads appear at incorrect times or ad break timing is inconsistent:

1. Verify ad break markers in content:
   + Check that SCTE-35 markers are properly placed in your origin content
   + Verify ad break duration matches actual ad content length
   + Confirm that ad break timing aligns with content boundaries
   + Validate SCTE-35 marker format and timing accuracy in your origin manifests
   + Test ad break markers with different content types (live vs VOD)

1. Check CDN caching impact on timing:
   + Ensure manifest TTL is set to 0 to prevent timing drift
   + Verify that time-sensitive parameters are not being cached
   + Check for clock synchronization issues between the content source, MediaTailor, and the CDN
   + Monitor for timing drift in long-running live streams
   + Verify CDN edge server time synchronization with NTP

1. Validate SCTE-35 marker implementation:
   + Verify EXT-X-DATERANGE tags include proper SCTE35-OUT and DURATION specifications
   + Check for paired SCTE35-OUT and SCTE35-IN markers when using explicit cue-in timing
   + Validate START-DATE timestamps align with actual content timing
   + Test different SCTE-35 marker formats (duration-based vs paired markers)

1. Test ad break timing across different scenarios:
   + Compare ad break timing with direct MediaTailor requests vs CDN requests
   + Test timing consistency across different CDN edge locations
   + Verify ad break timing with different player types and buffering behaviors
   + Monitor timing accuracy during peak traffic periods

1. Debug timing issues using logs and monitoring:
   + Enable debug logging to track ad break processing timing
   + Monitor CloudWatch metrics for ad insertion timing patterns
   + Check CDN logs for timing-related request patterns
   + Use player debugging tools to verify ad break timing from client perspective

**Expected timing tolerances:**
+ Ad break timing should align with SCTE-35 markers in your content
+ Ad duration should match the duration specified in your ad decision server response
+ Clock synchronization between content source, MediaTailor, and CDN should be within 1 second
+ SCTE-35 marker timing should be accurate to within 100ms of actual content timing

**Additional troubleshooting resources:**
+ For SCTE-35 marker format and implementation, see [Integrating a content source for MediaTailor ad insertion](integrating-origin.md)
+ For debug logging setup and timing analysis, see [Generating AWS Elemental MediaTailor debug logs](debug-log-mode.md)
+ For CDN caching configuration and timing impact, see [Caching optimization for CDN and MediaTailor integrations](cdn-optimize-caching.md)
+ For comprehensive testing procedures including timing validation, see [Testing and validation for CDN and MediaTailor integrations](cdn-integration-testing.md)
+ For monitoring ad insertion timing and performance, see [Monitor MediaTailor CDN operations and performance](cdn-monitoring.md)

**Success criteria:** When resolved, ad breaks should appear at precisely the times specified by SCTE-35 markers, with consistent timing across all CDN edge locations and player types. Debug logs should show accurate ad break processing timing without drift or synchronization errors.