When I start to render my videos the output file contains some "sound artifacts". I mean, sometimes the sound oscilates. Here is an example:

http://www.youtube.com/watch?v=qao52shBWgQ

At 0:13 and 0:14 the sound is not correct. There's something wrong. Can you notice it? Thanks.

Ps: no audio effects were used and I use latest kdenlive svn. The original audio track was AAC encoded from a Flip Ultra HD pocket cam.

I have had some audio problems with Flip HD videos as well (most annoyingly, the video's sound sometimes stops playing in Kdenlive). I have found that if I convert the Flip's video files to .mkv instead, then I have no problems. This command provides a lossless conversion:

ffmpeg -i VID00001.MP4 -acodec copy -vcodec copy VID00001.mkv

Of course, change the input and output filenames to match the video you are trying to convert. In my case, I created a script to batch convert an entire folder of Flip videos at a time. Here is the script:

#!/bin/bash
mkdir flipconverted
for f in *.MP4; do ffmpeg -i "$f" -acodec copy -vcodec copy "flipconverted/${f%.MP4}.mkv"; done

Copy the above script into a text editor and save it as "flipconvert". Open a terminal and navigate to the folder where you created your "flipconvert" script, and then type the following two lines, each followed by the enter key:

chmod +x flipconvert
sudo cp flipconvert /usr/local/bin

After that, you should be able to type "flipconvert" in a folder of Flip videos, and they will all be converted to .mkv and placed in a subfolder called "flipconverted".

Note: these instructions are for Ubuntu, but should work on most other distros as well.