Proof of play: what it proves and what it does not
Proof of play is a log entry recording that a specific piece of content played on a specific screen at a specific time. It is the closest thing this channel has to a verifiable delivery record, and it is a considerably stronger basis than a planned schedule.
It is also frequently described as though it measured something it does not.
What does a proof-of-play log contain?
Content identifier, screen identifier, timestamp, and usually duration. Better implementations add a confirmation that the content rendered rather than merely that it was scheduled.
The rendering confirmation is the part that distinguishes a real proof of play from a schedule with a timestamp attached.
What does it prove?
That the content played. That is a real and useful claim: it verifies delivery, it supports billing, and it allows under-delivery to be detected and remedied.
It does not prove that anybody was present, that anybody looked, or that anybody understood. Those are separate questions requiring separate evidence, and no log can answer them.
How does it relate to impressions?
An impression figure is generally plays multiplied by an audience estimate for the screen and time. The plays half is measured; the audience half is modelled, and the modelling is where the uncertainty lives.
A network that separates the two in reporting is being transparent. One that reports only impressions has combined a measurement and a model into a single figure that cannot be interrogated.
Can proof of play be audited?
Yes, and it is one of the more auditable parts of the channel. Logs can be reconciled against the plan, against uptime, and against the invoice, and discrepancies are straightforward to identify.
Ask whether logs are available at the level you would want to audit. A summary is a report; the underlying log is evidence.
What are the limits?
The log records the player's view of what happened. A player that rendered content to a screen that was switched off, or to a display with a fault, will log a play that nobody could have seen.
That is the specific gap between proof of play and delivery, and it is why uptime and playout should be reported together rather than separately.
How should it be used in measurement?
As the compliance record for a test. A lift analysis should exclude or flag stores where delivery fell materially short, and proof of play is the data that makes that possible.
Without it, a flat result cannot be distinguished from a campaign that did not run properly, which is a common and expensive ambiguity.
What should a contract specify?
Log availability, granularity, retention and format. Those four determine whether the record is usable when a question arises months later.
Frequently asked questions
Is proof of play an industry standard?
Logging is standard practice and the specifics vary between platforms. What matters commercially is whether the network will provide the log and at what granularity, which is a contractual question rather than a technical one.
Does it replace independent verification?
It is first-party evidence, which is stronger than nothing and weaker than an independent audit. Where the value at stake justifies it, third-party verification of the logs is available in the wider out-of-home market.
Can logs be reconciled with the invoice?
They should be, and doing it once at the end of a flight is a reasonable discipline. It is the check that detects under-delivery, and most buyers never run it.
What granularity is useful?
Play-level by screen is ideal and daily by store group is workable. Anything coarser than that cannot support a compliance analysis.
How long should logs be retained?
Long enough to cover any measurement or billing dispute, which is months rather than weeks. Confirm the retention period before you need it.
Does a screen count as delivered if nobody was in the store?
The play occurred and the audience did not, which is exactly why plays and audience estimates should be reported separately. Conflating them is how an impression figure becomes unfalsifiable.
What about programmatic buys?
The same records apply and the transaction layer differs. Industry practice on digital measurement standards is discussed by bodies such as the IAB.
Should proof of play be in the reporting pack?
A summary should, with the underlying log available on request. A buyer who never asks for it still benefits from the network knowing it can be asked for.
What is the single most useful thing to do with it?
Reconcile it against the plan and the invoice once per flight. It takes an hour and it is the only way to know the campaign ran as sold.
### How should logs be used during a flight rather than after?
As an early warning. A weekly check against the plan catches under-delivery while there is still time to remedy it, which is considerably more useful than discovering it in a post-campaign report.
That requires the reporting cadence to be weekly rather than at the end, which is a specification to agree in the plan. Most networks can provide it and few are asked.
Can proof of play support a co-op claim?
It is unusually good evidence for one, because it records what actually played where. Whether it satisfies a specific programme depends on how that programme's evidence requirements are written.
### What should be retained after a campaign?
The summary in the report and the underlying log in a form that can be reopened. Disputes and measurement questions arrive months later, and a log held only by the network is a record you do not control.
Agreeing the retention period and the format in the contract is straightforward and it is rarely done, which is why so many post-campaign questions end in recollection.
Can logs be independently audited?
Third-party verification exists in parts of the out-of-home market and adoption varies. For a large commitment it is worth asking whether the network has been audited and what the scope was.
Does a log prove viewability?
No. It proves the content rendered, which is a delivery claim. Viewability and attention are separate questions requiring different evidence.
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