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Re: Sync all over the place

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Ken Glaza
Re: Sync all over the place
on Apr 2, 2010 at 12:40:14 am

I really didn’t want to get into this level of complexities. There is no room to teach here. I like a brisk conversation but can we dispense with the slams Mr. Moderator?

Audio- A single file example!
“MP3 files are segmented into zillions of frames, each containing a fraction of a second's worth of audio data, ready to be reconstructed by the decoder.” Left and right audio are interlaced (“to unite, interwoven, interlocked, intermixture”; Websters’ Third c1966); according to the codec to create a single file. Look at this simple example.

http://www.mp3-converter.com/mp3codec/mp3_anatomy.htm

Video and Audio in one file!
A bit more complex because they are described as being a container type of file used to provide a single file of audio and video to the user.
“A container or wrapper format is a meta-file format whose specification describes how data and meta-data are stored (not coded). By definition, a container format could wrap any kind of data. Most container formats are specialized for the specific requirements of the data. For example, a popular family of containers is found among multimedia file formats. Since audio and video streams can be coded and decoded with many different algorithms, a container format can be used to provide a single file to the user.”
http://www.answers.com/topic/container-format-digital
I have provided a link so that you can see a graphic of the single file structure that a popular type of AV file is made of.
http://graphcomp.com/info/specs/ms/editmpeg.htm
In this container format, it is almost always with out exception that audio is interwoven with picture as the single file is created. Some do it similar to the MP3 frame by frame method and others use big groups of pictures (GOP) with different compression schemes. Some codecs break the sound into a frame by frame timed piece so that editing would be the easiest. But it is up to the secret sometimes pricy codecs used to encode and decode the interwoven audio with video files.
Once again maybe the encoder or decoder is missing “Container” and Coding information and the settings need to be looked at. Or if they are separate audio and video files it might be the choice of a few settings that are not matched as well. I am suggesting the checking of drop v non drop frame for the video compatibility, sample rates, even bit depth, audio and video and who knows what else may be an option. Granted I could have said that "Some softwares keep audio and video in separate files". Nothing lost or gained here, nothing reversed.
Truly Your Forensic Expert Ken Glaza


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