Dynamic ad insertion and substitution are increasingly popular to monetize OTT services. A key enabling technique is the signaling of timeslots for insertion or substitution. In practice, SCTE 35 has been used for this, but OTT implementations have been somewhat inconsistent in practice. This paper highlights advances in ad insertion from both practical and a standardization perspectives to realize consistent and robust ad slot signalling in end-to-end OTT workflows. Guidelines for server or client-based ad substitution using SCTE 35 in DASH and ISO base media file formatted files are presented. It addresses the SCTE 35 fields, ISO BMFF and DASH fields and their relationship. The guidelines have been recently developed through joint discussions by DVB and SCTE resulting in publications as DVB-TA part 3 and SCTE 214 (2022) (and in its upcoming guidance annex) respectively. Additionally, this paper provides examples and illustrates specific use cases, such as the early termination of ad breaks, insertion of ads, and MPEG DASH period splitting. To showcase usage in a DASH manifest manipulator a cloud function implementation for period splitting of large dynamic presentations in real-time is described. Additionally, this paper details emerging techniques to carry SCTE 35 upstream in ISO BMFF and CMAF timed metadata tracks based on the recently published event message track ISO/IEC 23001 – 18 specification. This metadata track format mainly targets storage and upstream use cases. An implementation is described that generates example files based on this format with ad slot signaling and it is used to implement a distributed live CMAF uplink.