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Topic: Several doubts about adding CRC to MP3s... (Read 2176 times) previous topic - next topic
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Several doubts about adding CRC to MP3s...

Hi all.
I've been reading some LAME documentation and I've founded the "-p" switch, that
"adds CRC error protection" to the MP3 files...

Searching here I've founded some data about this, but the question is still very
unclear to me...

The conclusions I've got to now (advice me If I'm wrong please).
- CRC adds a little data to de MP3s frames, a checksum.
- The data of the CRC is really small (maybe considered "unapreciable")
- If some data in the MP3s frames changes the CRC check will fail (logical).

A now the doubts that round me...

1.- This CRC data may cause problem of reproduction in some players? Its a kind
of standard o is more likely a "tweak" of the MP3 file structure...

2.- This CRC info may be used to repair damages MP3s? How?

3.- Its possible to add / remove CRC data to a file with / without it?

4.- Changing TAGs of the files affects CRC, or the CRC data is attached to the
"musical data" itself instead the whole file?

And last resuming:
Is recomended to use this switch?

Best regards and TIA for your answers.
b:.

Several doubts about adding CRC to MP3s...

Reply #1 –
Hi,

Quote
This CRC data may cause problem of reproduction in some players? Its a kind
of standard o is more likely a "tweak" of the MP3 file structure...

No.. it shouldn't cause any problem. If I'm not mistaken, you can basically add any data in the frames - as long as you don't refer to it.

Quote
2.- This CRC info may be used to repair damages MP3s? How?

You can't repair anything with it. It's only an error detection feature.

Quote
3.- Its possible to add / remove CRC data to a file with / without it?

In theory, yes. You basically have to drop 32 bits of audio data in each frame, and put in the CRC's.

Quote
Changing TAGs of the files affects CRC, or the CRC data is attached to the
"musical data" itself instead the whole file?

The CRC is calculated on the musical data..  only a mp3gain (which patches coefficients in the audio) would make crc's wrong.

Quote
Is recomended to use this switch?

Nope. There are far better ways to ensure integrity (and/or fault-tolerance) of your data.

Several doubts about adding CRC to MP3s...

Reply #2 –
Quote
Is recomended to use this switch?

as far as i remember, its only usefull for streaming
 

Several doubts about adding CRC to MP3s...

Reply #3 –
Thanks for solve my doubts!
Best regards.

b:.