Audio/Video Out-of-Sync
Firstly, I thiNK we should aware of some basic info about Audio/Video(A/V) out of sync. Both situations: audio leading video and audio lagging video. Generally description, that is the audio is lagging behind/leading the video picture, or the pictures are moving at a faster/slower speed than soundtrack. Figuratively speaking, have you ever heard someone talking to you before you saw his mouth opening? Weird? Contrary to common understanding that light travels faster than sound? Actually, this weird audio/video out of sync phenomenon is widely present in various portable digital devices, video conversion and playback on PCs.
International Telecommunications Union Radiocommunications Sector recommendation (1998), average A/V out-of-sync detectability threshhold for ordinary people was set at about 45 milliseconds for audio leading video and 125 ms for audio lagging video, and A/V out-of-sync acceptability thresholds — meaning passing that people will reject the video, are set at 90 ms for audio leading video and 185 ms for audio lagging video.
Why, you might ask, is the tolerance tighter for audio coming before the video than lagging behind the video? This is because in our daily lives, human hearing system is more tolerant to audio lagging video than preceding video, due to the fact that light travels much faster than sound(30,000km per second for light, a few hundreds to a few thousands metres per second for sound depending on transmitting environment). We are used to hearing sound after seeing the actual view if the video/sound source is away from us, such as watching sports events in an open-air stadium. But we are easier to feel uncomfortable with the reversed situation where sound comes before the video that generates the sound.
For more info in wikipedia.
Reasons for Audio/Video Out-of-Sync
Is this a file issue? maybe the file is corrupted or otherwise screwed up? or is this a player issue? Most people do not realize that the audio and video inside of any file are two separate streams. This means that when someone tries to play an edited movie, the video starts and then the separate audio starts after. Because of this, it is very easy for the audio to play out of sync with the video. Actually, it also exist subtitle/audio/video out of sync problem, we can use the similar reason to explain it. But the subtitle problem is easier to deal with, it just a subtitle file, just a time display adjustment problem.
To be fair, A/V out-of-sync problem is not limited to videos on PCs. In theory and in practice, all digital video equipment have video/soundtrack sync problem. The first generally accepted reason for A/V out-of-sync is that digital processing of video signal is always more resource intensive than digitally processing audio signal, therefore video processing always needs more time than the corresponding audio processing.
The second generally accepted reason for A/V out-of-sync on digital video is wrongly produced sampling clock. This could come in many different flavours. One typical situation in PC video editing is that the sampling clock used by the PC differs from that used by the original video source.
The third common cause of audio/video out of sync is using the third party software to do realtime video / audio compression. Most video capture processes on PCs need to compress video in realtime into a suitable format for a particular application: analogue video need to be compressed in DV, MPEG, or streaming format, DV video need to be compressed into MPEG or streaming format, etc.
The fourth, reality is that people download video/movie off youtube, google, yahoo, dailymotion etc social video sites, because of the video formats incompatible, we need to convert video to various formats for different portable devices, so we need to adjust the video to the right Frame Rate(frames per second), Frame size, Pixels. Also, device itself such as configuration, resolution, all those are likely lead to the out-of-sync problem. Remember that? The interrelationship is that audio&video inside of any file are two separate streams.
Besides, it isn’t only with eps that are cut also download files that aren’t complete downloaded might lead to the video/soundtrack out-of-sync problem. Concerning the video quality losing problem, will encounter in other post.
Possible Ways to Fix/Reverse It
– When I sync albums to my iPod Touch they don’t seem to play in the order they are listed. So far I have done a soft reset (no joy), deleted the albums and re-loaded them (no joy), and a few minutes ago I did a complete restore and the songs are still out of sync. I checked on itunes to see if the files are in order and they are fine. I loaded the same albums onto my iPhone and they play in order as they should do.
– I just went to Settings –> General –> Reset –> Reset All Settings. Not quite sure what settings were reset or changed in the first place for that matter but it works fine now. Whatever, it’s an efficient way.
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