Want to use different tracking url by mediafile

[kyungtae]

In DSP side, I want to know what mediafile was played among multiple files.
ChatGPT 4o replied below as an answer. Is it valid method?
If not, is there any other method ?

<VAST version="3.0">
  <Ad id="12345">
    <InLine>
      <Creatives>
        <Creative>
          <Linear>
            <Duration>00:00:30</Duration>
            <TrackingEvents>
              <Tracking event="start">
                <![CDATA[http://tracking.example.com/start?file=video1]]>
              </Tracking>
              <Tracking event="start">
                <![CDATA[http://tracking.example.com/start?file=video2]]>
              </Tracking>
            </TrackingEvents>
            <MediaFiles>
              <MediaFile id="video1" delivery="progressive" type="video/mp4" bitrate="1500" width="640" height="360">
                <![CDATA[http://example.com/video1.mp4]]>
              </MediaFile>
              <MediaFile id="video2" delivery="progressive" type="video/mp4" bitrate="1500" width="1280" height="720">
                <![CDATA[http://example.com/video2.mp4]]>
              </MediaFile>
            </MediaFiles>
          </Linear>
        </Creative>
      </Creatives>
    </InLine>
  </Ad>
</VAST>

[aleksUIX]

That suggested markup will not do what you want. Two <Tracking event="start"> entries in the same <TrackingEvents> block both fire on start, regardless of which <MediaFile> the player selected. Tracking events live on the <Linear> creative, not on individual media files, so there is nowhere in that structure to express "this URL, but only for video1".

VAST has a purpose-built macro for exactly this: [ASSETURI].

Field	Value
Introduced	VAST 3.0
Support	Optional
Contexts	All tracking pixels
Description	The URI of the ad asset currently being played

So one tracking URL, with the player filling in which file it chose:

<TrackingEvents>
  <Tracking event="start">
    <![CDATA[http://tracking.example.com/start?file=[ASSETURI]]]>
  </Tracking>
</TrackingEvents>

The player URL-encodes the substitution, so you get file=https%3A%2F%2F...%2Fvideo1.mp4 back and can map it to a rendition on your side.

Two caveats worth knowing before you build on it:

1. Support is marked Optional in the macro spec, so player coverage is not universal. Plan for the macro arriving unsubstituted and treat a literal [ASSETURI] in your logs as "unknown rendition" rather than dropping the row.
2. It gives you the URI, not an ID. If your renditions share a filename across CDN paths, or if you sign or cache-bust the URLs, normalise before matching.

If you need something stronger than best-effort, the reliable answer is server side: make each <MediaFile> URL unique to a rendition on your own origin and correlate at delivery time. That does not depend on player macro support at all.

Since you are on VAST 3.0, [ASSETURI] is available to you. [MEDIAPLAYHEAD] in the same macro family is often useful alongside it if you also want playback position on the ping.