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I'm using a Powershot S100 with CHDK. The default video bitrate of the S100 is around 4 MByte/sec at the highest quality. Using CHDK and the options "Mode=Quality" and "Quality=99", you can get 14MByte/sec video.

I just did a quick test with a low-light scene. The noise leads to blocking in the 4MByte/sec version. In the 14MByte/sec version, the noise is much crisper, and the blocking is gone.

I wonder is there a sweet spot here? 14MByte/sec is clearly too much to store, but looks better than 4MByte. Is there a particular quality level I should choose?

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  • Although this would still probably be closed as "opinion based" there - what settings you choose depends on what you're going to do with it.
    – Philip Kendall
    Dec 11 '14 at 21:54
  • More likely too broad. I have edited to hopefully prevent it from being too broad.
    – AJ Henderson
    Dec 12 '14 at 14:47
  • do you actually mean MBps and not mbps? Codec data rates are almost exclusively given in mbps normally, which is bits, not bytes.
    – AJ Henderson
    Dec 12 '14 at 14:57
  • Yes, it's actually megabyte, these are values I calculated from the filesize. 14 MByte per Second is therefore 112 MBit.
    – LTR
    Dec 13 '14 at 1:18
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No, there is no sweet spot for compression, whether it is on a camera or in encoding after the fact. The needed data rate depends heavily on the content being recorded and is a complex field, though the best bet to handle it simply is to try adjusting it and decide when it works for your needs. You can eventually get an idea of the quality from each bitrate for your camera, but we can't really give you guidelines as both noise level and the particular encoder used by your camera will also impact the way things turn out.

One important caveat to keep in mind when dealing with compression on a camera is that if you are going to edit the footage, you want to make sure you use a high enough quality that re-compressing after editing does not result in quality loss either. With lossy compression, each additional compression results in further quality loss and a video that looks fine initially may fall apart when compressed for final output. The larger your source videos are, the smaller you are likely to be able to compress your final video to. You may also want to shoot All-I if it is an option because this format is far more efficient in editing software than compressions that are group of picture based (IPB), though they also take far more space to get good quality.

Also, you say that 14MBps is obviously too high, but I would challenge you that it is not obviously too high. Uncompressed, 1080p video at 24fps would still take 150MBps or 1194mbps. You are still compressing over 90% at 14MBps. Bluray will often use in the neighborhood of 35 to 50mbps which is still up to almost half of the 112mbps data rate you quoted as the max. Particularly if that is All-I, 112mbps is not an unexpectedly high value at all.

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  • Wow, I wasn't aware how large uncompressed 1080p actually is. My camera is encoding H264, but I'm pretty sure, since it runs onboard a tiny consumer camera, that the compression level is much lower than H264 encoded on a Desktop PC with lots of CPU power. Therefore, it might well be that 112mbps from my camera looks equal to a proper 50mbps encode.
    – LTR
    Dec 13 '14 at 1:21
  • @LTR - exactly, single pass encoding on a camera in real-time isn't going to be as good at compressing as something like a 2 pass encoder that can run sub-realtime in order to maximize quality.
    – AJ Henderson
    Dec 13 '14 at 5:38

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