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Command Prompt Anomaly


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#1 mykul

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Posted 28 January 2006 - 04:09 PM

I use command prompt copy syntax to combine consecutive tracks of opera cds into a few longer files. This only works when the individual .wav tracks are first converted to mp3 files. Why doesn't the same syntax combine the original wav files? The command prompt window indicates the tracks have been combined but only the first file of the set actually plays.

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#2 Platypus

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Posted 28 January 2006 - 07:05 PM

This happens because of the different way data is handled in the different file format.

MP3s are formed of many independent "frames", each frame has its own header describing the contents so the player knows what to do with the data. When MP3s are concatenated, it just becomes a bigger MP3.

A WAV has a header which describes the format of the particular file, including the size of the data "chunk". If you concatenate WAV files, this header information is unchanged, so a player doesn't know about the extra data.

To combine WAV files, you can bring them into a WAV editor like the free Audacity, adding each to the end of the existing sample then save the complete file, thus updating the header.

This is much more involved than concatenation, and I don't recall if Audacity has a batch processing facility. However I think the original free version of Cool Edit (now Adobe Audition) did do batch processing, and can probably still be found with a Google search.

Edited by Platypus, 28 January 2006 - 07:08 PM.

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#3 mykul

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Posted 03 February 2006 - 12:31 PM

Thank you platypus. It sounds as though all the files have been combined but the player is only reading the amount indicated in the header of the first file if they are .wav, but not if they are .mp3?

#4 Platypus

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Posted 04 February 2006 - 06:04 PM

the files have been combined but the player is only reading the amount indicated in the header of the first file if they are .wav, but not if they are .mp3?


Yes, you've understood correctly. With a concatenated .wav file, the player is still only pointed to the data in the first file and doesn't know the rest has been added on. An .mp3 player keeps playing as long as it finds more frames in a file, and each frame has its own header information defining its contents.

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