Video edited out of synch but then fooled it to synch perfectly; How come?

[johnharlin]

I have a number of videos all with the same format that I need to trim. I trimmed down a 1 hour 8 minute .flv movie to 57 minutes with the following properties

Codec: H264 - MPEG-4 AVC (part 10) (avc1)
Resolution: 640x360
Frame rate: 30
mime type video/x-flv
ffdshow video decoder
ffdshow audio decoder

Type: Audio
Codec: MPEG AAC Audio (mp4a)
Channels: Stereo
Sample rate: 44100 HZ

I tried to open the movie in AVI Demux several times but it just got stuck and could never even open the movie.

So I used AVS remaker. Here I managed to trim the movie down but then it came out totally out of synch with the sound by
at least 5 seconds. I then was able to open it with AVI demux and tried to use the time shift function but for some reason
no matter what I did, it didn't seem to have any effect.

I then reasoned that it might have something to do with key frames and if so, if I trim the movie down right before the opening where the person begins to talk then the speaker might not be out of synch with the sound.

I did that and the result was that the speakers voice began many seconds before the speaker began to speak but then when the speaker visually began to speak the sound started all over again and the speakers mouth and the sound were in perfect synch and it stayed like that for all the other speakers in the movie.

Somehow, someway by luck maybe, I got this movie synched though it has that weird start, however, I don't really understand what's going on here. Does anyone understand?

I have noticed in the past that when I converted an mp4 video to h.264 in a smaller frame size, it came out with synch problems. Could it be that h.264 is not good with synching video to audio. Should I not use that format?

Should I try a different video editor that won't result with synch problems?

[Selur]

you should first check if you input file is vfr because it sound like it and when editing or remuxing a vfr file, you also need to take care of the time codes,...