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In my output video there a pulse that occurs after the number of frames specified in the "GOP Size" setting. With the setting of 18 that I have in the image shown below, the pulse occurs every 18 frames. During this "pulse", the video seems to move to a lower picture quality and then quickly returns back to a high quality.

Here are my output settings: enter image description here

If I set "GOP Size" to zero, the picture quality of the video degrades substantially. The maximum value for "GOP Size" seems to be 100, so the pulses occur a little over 3 seconds apart.

Is there anything I can do to alleviate this?

Any idea what I might be doing wrong?

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    $\begingroup$ I think you need to increase the bitrate, or at least the gap between minimum and maximum. A GOP is group of pictures, it contains a full image followed by areas of the image that have changed. By having to keep the bitrate within a narrow margin the full image uses most of the bitrate so the following frames need to use less to prevent going over the maximum, therefore the lower quality to maintain the bitrate within given limits. $\endgroup$ – sambler Nov 20 '13 at 11:41
  • $\begingroup$ That's a typical behaviour in the MPEG-4 Codec. You should switch to H.264 and that should be much better. Worked for me. Some people advice to set the GOP to the Framerate, others say half the Framerate, maybe that helps as well. $\endgroup$ – Samoth Jan 27 '16 at 20:58
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The problem may be caused by some sort of glitch in the encoder included in Blender. The poor quality can be avoided by using lossless output. In v2.71 this is done by choosing H.264 format under Encoding, and ticking the Lossless Output box.

enter image description here

Here is a detailed video explaining lossless rendering in Blender.

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The minimum bitrate is the problem. You need to set the Minimum and Maxium bitrate number to be the same. That fixed it for me. :)

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