[MPlayer-users] mencoder to join files: keyframes gone?

[Johan]

I've sucessfully used mencoder and -copy switches to concatenate several 
  avi files. The original files all seek very well; without the floating 
colored blocks effect.  The concatenated file plays perfectly (great 
sync), but seeking results in upto a second or two of image degradation 
(ie, blotchy blobs) before quality is restored.  I'm concluding that the 
original had more keyframes than the concatenated version. The 
concatenated version is also smaller than the sum of the parts, so this 
may well be the case.

Is there someway to request more keyframes (or that all keyframes are 
kept?), or am I misdiagnosing the problem?

the command:

cat "$1"*avi | mencoder -ovc copy -oac copy -forceidx -o "$1_joined.avi"


As a contrast,

avimerge -i "$1"*avi -o "$1_joined.avi"

seeks fine, but has sync problems more often than not.

Johan