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Choppy encoding

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Tim BentleyChoppy encoding
by on Oct 18, 2014 at 1:53:55 pm

Hi all - I wondered if anyone might be able to help with a small encoding issue. This film:

has a couple of moments (1m05s and 1m11s) where the video becomes quite choppy. It was encoded using the bog-standard Vimeo 1080p HD 2-pass setting in Media Encoder (25fps) from a lossless (and not choppy) AE export. I'm using AE CC 2014 on an iMac - the pencil graphics are Tiff sequences and the other images are composited in AE using imported camera data.

I've tried to research the subject online but apart from the fact that the very fast movements are causing this, which I'd already figured out, I can't find any advice on how to address an issue which only appears for such a brief moment(s).

Any tips / advice gratefully appreciated!

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David BaudRe: Choppy encoding
by on Oct 18, 2014 at 2:39:59 pm

Have you played your H.264 encoded file on your computer before sending it to Vimeo? do you see the same issue?

It would help if you could tell us your chosen frame rate of compositing.
Also what is the bit rate of your Vimeo 1080 HD output?

David Baud
Post & VFX
Denver - Paris

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Tim BentleyRe: Choppy encoding
by on Oct 18, 2014 at 6:04:39 pm

Yes I certainly played the video before uploading it, and it's nothing to do with the Vimeo player.
The frame rate is 25 fps and I'm using the default 2-pass Vimeo settings, for which the target and maximum bit rates are 5 Mpbs. I've tried at 7 and 10 but the problem persists, though less noticeably.

Maybe I'm just being too conservative with the bit rate, but it seems odd to practically double the file size for the sake of a few seconds of choppiness. That's what I'll do if necessary but I've never had this problem (or never so pronounced) at 5 Mbps before (VBR obviously).

Happily, upgrading to Yosemite has bricked my backup drive which has given me something to keep my mind off it :-)

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Doyle LewisRe: Choppy encoding
by on Oct 24, 2014 at 7:31:56 pm

According to Kush's guage (a formula for calculating adequate bit-rates,) Frame height x frame width x frame rate x motion scale variable(1,2, or 4) x Kush's constant variable(0.07). You get the number of bits per second required for a constant bit rate. For variable you take 3/4 of that number. That being said your target bitrate should be around 10.89Mbps. If you would like a better explanation for that number look at the link below.

Now you said you tried around that bitrate and it didn't fix the problem. the fact that you said that the file had this problem before sending it to vimeo means that it is not vimeo's display/compression settings. Now when I looked at the video I did see a couple small artifacts in the color especially in the papyrus colors, but I did not see which choppiness you were referring to exactly. Was it the aliasing you were referring to? because there is quite a bit of that, but that is naturally going to happen on a h.264 compression of such tight small lines.

Doyle Lewis, Assistant Videographer

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Tim BentleyRe: Choppy encoding
by on Oct 24, 2014 at 7:41:37 pm

Thank you for your reply, I should have updated this post. In fact I finally went for exactly that target bit rate (more or less, it was around 12). I think I was just surprised by the amount it was necessary to increase the bit rate by before I was able to get rid of artefacts which appeared for such a short time. Anyway I'm glad you couldn't detect any choppiness as I guess that means the problem's solved. Thanks again!

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