How I can resolve this problem?

What do you mean by this? It makes no sense..... Can you please explain in more detail of what you are trying to accomplish?

Every single words on the audio on the video is followed by the same words with few delays.

We know what an echo is. What we need is more details about your exact problem. Is it a single video, several videos from a single source, or from different sources? And what are the sources? What format(s) are they in and what codecs do they use? Does the problem happen with every multimedia player you try them on, or just one? What have you tried so far to fix the problem? And so on.

If the echo is in the original audio itself, then the only likely option is to separate the audio and video streams with a media editor of some kind, such as ffmpeg or avidemux, run the audio through a sound editing program like audacity or sox to remove the echo (if possible), then remultiplex the fixed stream back in with the video.

Ah ok.
I use mplayer.
The problem is present on different video (flv) but don't on all videos.
Naturally even after a format conversion on webm the problem remain the same.
Now i have found this article:
removing echo
unfortunately seem there isn't any way for perform an automatic operation for remove similar issue.