Brief bitrate drops when using "Constant Bitrate"


Ever since HitFilm 3 was released, I've been dealing with this problem.

When I take any sort of footage, run it through HitFilm and want to render it using Constant Bitrate in 60FPS, regardless of the other settings, I see massive bitrate drops during playback. Like it plays back beautifully and suddenly the footage goes completely dithered for a split-second, then back to the normal quality.

I need to use Variable Bitrate to avoid it, however Variable seems to have some of the same tendencies albeit much, much less visible. 

Here's an example. Granted it's a fairly poor example but gives you an idea what I'm talking about; - Obviously this is heavily compressed due to being a .webm, however what I'd like to point out is the sudden massive dither / blur that happens a few seconds in, twice in a row. That is VERY pronounced when viewing it back in 1080p at a 100k+ bitrate. 

And it happens every single time, despite of the original source, whether it's a game recording fresh off ShadowPlay, something rendered pre-hand in Sony Vegas or otherwise. As long as I use Constant Bitrate, it happens.



Windows 8.1

5960x @ 4.4GHz

2 x Asus 980 



  • NullUnit
    NullUnit Posts: 779 Just Starting Out
    edited January 2015

    I have also had this happen to me. So, far it seems (for me) that this really only happens if I use a compressed mp4 file as my source footage. For instance, I wanted to do a quick color grade on a clip I took with my samsung galaxy. The format it records in is, of course, compressed mp4. I didn't feel like converting it to an editing format so I imported it directly into HF3 and got pretty much the exact type of rendering issues I see in your clip and they would happen in the same place every time. Same with when I needed to help a friend with a quick edit and all they had were compressed mp4s. 

    So, I was able to "fix" the problem by taking the time to converting the mp4s into DNxHD (a proper editing format) and the renders looked fine after that. I wonder if the screen capture software that your using is recording in mp4 or a similar compressed format?

    Here is a thread with more details about good file formats for HF.

  • Sethos
    Sethos Posts: 9


    Appreciate the reply.

    My primary source of footage is indeed .mp4 as I'm working on video game machinimas primarily. ShadowPlay, Nvidia's recording software outputs in .mp4 exclusively and when I render / re-render anything in Vegas Pro 13, I use MainConcept AVC/AAC which also outputs in .mp4. 

    So it's very likely that it's the problem.

    However, I have no real option of changing the output format. Would you have any recommendations for a (Free?) decent piece of converting software I could use as a bandaid fix for now?

    In the long run however, it would be great if the issue was sorted as I sometime work with tons of .mp4 file recordings, having to convert everything would just get tedious in the long run.

    I like to export / render with HitFilm, as Vegas' 60FPS renderings have caused some headaches in the past for me. 

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