# Negative Sample deltas in STTS box

**URL:** <https://community.wowza.com/t/negative-sample-deltas-in-stts-box/51596>\
**Category:** Wowza Streaming Engine\
**Tags:** recording\
**Created:** [July 10, 2018, 2:35pm UTC](https://community.wowza.com/t/negative-sample-deltas-in-stts-box/51596 "2018-07-10T14:35:02Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Moreno\_Gentili](https://avatars.discourse-cdn.com/v4/letter/m/838e76/32.png) [@Moreno\_Gentili](https://community.wowza.com/u/Moreno_Gentili)\
**Post date:** [July 10, 2018, 2:35pm UTC](https://community.wowza.com/t/negative-sample-deltas-in-stts-box/51596/1 "2018-07-10T14:35:02Z")

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Hello there,

I’m having an issue with recorded RTSP streams using the **rtp-record** media caster type. The mp4 recording contains some negative sample deltas, which are shown here in Mp4 Explorer as being huge since they’re read as unsigned ints, as it should be.

According to the [specification](http://l.web.umkc.edu/lizhu/teaching/2016sp.video-communication/ref/mp4.pdf#page=32), “_d\*\*urations in the ‘stts’ box are strictly positive (non-zero)_” and this is causing us unresolvable synchronization and clip issues which appear more evident for longer videos.

We’ve noticed that this issue is **not** present when we use the **rtp** media caster type and then record the stream using an incoming stream recorder.

Why do the rtp-record media caster and the stream recorder show this different behavior?

Thanks.