These appear to be the relevant errors:
Maybe the info might help? Data is not aligned
JojuOct '16
I solved the problem for myself. I opened the MLT as file and exported it after that to mp4-file. And everything is now ok. But I still do not understand, why the export failed.
swscaler @ 0000000052567300] Warning: data is not aligned! This can lead to a speedloss
wav @ 00000000325c2e40] parser not found for codec pcm_s16le, packets or times may be invalid.
wav @ 00000000325c2820] parser not found for codec pcm_s16le, packets or times may be invalid.
[avi @ 000000003203a3e0] parser not found for codec msvideo1, packets or times may be invalid.
[avi @ 000000003203a3e0] parser not found for codec pcm_s16le, packets or times may be invalid.
[avi @ 000000003203a3e0] parser not found for codec msvideo1, packets or times may be invalid.
[avi @ 000000003203a3e0] parser not found for codec pcm_s16le, packets or times may be invalid.
[avi @ 00000000320342e0] parser not found for codec msvideo1, packets or times may be invalid.
[avi @ 00000000320342e0] parser not found for codec pcm_s16le, packets or times may be invalid.
[avi @ 00000000320342e0] parser not found for codec msvideo1, packets or times may be invalid.
[avi @ 00000000320342e0] parser not found for codec pcm_s16le, packets or times may be invalid.
[avi @ 000000003203a9e0] parser not found for codec msvideo1, packets or times may be invalid.
[avi @ 000000003203a9e0] parser not found for codec pcm_s16le, packets or times may be invalid.
[avi @ 000000003203a9e0] parser not found for codec msvideo1, packets or times may be invalid.
[avi @ 000000003203a9e0] parser not found for codec pcm_s16le, packets or times may be invalid.