Why are some files soo large when using rtmpdump?

[korexaj]

I have noticed that rtmpdump uses crazy amount of storage compared to other recording methods. e.g.

I was recording a stream using ffmpeg (for chaturbate) and after a while i thought i should record using rtmpdump to see difference in size.

The results are that the recording using ffmpeg came to around 300Mb (36min long) in 720p whereas when using rmtpdump the exact same stream came to around 900Mb and was 23min long because both werent started at same time.

So why a HUGE difference in size?