The only phone I've had a lot of personal experience with is my Lumia 920, so I'll use that as an example. It has 32GB of flash storage with 29.1GB available for use after formatting. System files consume 2.83GB, and let's assume we have 1.27 GB of critical apps, leaving us with 25GB to actually use for video. (I'm making a lot of assumptions so take everything with a grain of salt.) A sample video uses 20Mb/s of data, but it's not particularly high-motion or demanding to decode, so lets bump that up to 30Mb/s as a worst case scenario. This comes to about ~3.58MB/s of data that needs to be saved to storage. 25GB of storage = 25600 MB, so 25600/3.58 = ~7151 seconds of video, or about 2 hours worth. You're probably not recording 2 hours of high-motion video at a time, so that's probably not it. One of two scenarios is more likely: a) Your phone has an arbitrary cap on video length/size, or b) it has a 32-bit filesystem that only allows for files up to 4GB, so your phone stops recording at that point because no more data can fit in the file. You could try recording longer videos in an effort to get them to forcefully stop recording and then compare them and see what kind of common attributes they have.
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