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Subject: Re: Bad Recorded MP3s - may not be (solely) a DAC issue

Re: Bad Recorded MP3s - may not be (solely) a DAC issue

From: Bluechip <csbluechip_at_gmail.com>
Date: 2005-11-06

At 10:33 05/11/2005, you wrote:
>On 05.11.2005, Linus Nielsen Feltzing wrote:
>
> > Bluechip wrote:
> >> 1. Why does RB append a blank 4K ID3v2 header to the start of
> >> every file?
>
> > It's there for convenience, so that the file can be updated
> > with a valid tag without rewriting the entire file.
>
>Yes eaxactly. Rockbox did this all the time, but only for the
>first file when using time split. Recently it does this for all
>recorded files. One might argue that this might make joining the
>files a bit harder, but why would you split them in the first
>place if you want them joined? Recent version also always add
>a xing header with complete (basic) info.

I record shows with time-split to make preliminary editing easier - then
splice it all together as the last step ...working on massive files is
unbearable on my machine.

> >> 2. Each ID3v2 tag is followed by 212 (0xD4) 0's ...which
> >> afaict serve no purpose.
> >> Is this a bug, or is there something I don't know?
>
> > If there are 212 0's between the tag and the Xing header, then
> > it's a bug.
>
>The number of zero bytes before the xing header varies because
>the size of the xing header varies depending on the mp3
>samplerate. This isn't exactly a bug, at the start of the
>recording rockbox doesn't know the size of the xing header
>yet, but needs to reserve thespace in the file, so it simply
>reserves the possible maximum. Most often the actual xing header
>is smaller, hence the space. It has always been that way, but
>due to changes in the handling the amount of zero bytes also
>depends on the rockbox version.

http://www.codeproject.com/audio/MPEGAudioInfo.asp#Anchor-4.-34080
(and others) seem to suggest that the header is always the same length -
can you point me in the right direction for the information you have please?

>This could be properly fixed by adjusting the size info of the
>id3v2 tag to include this empty space.

Yes, that is probably the smartest option, as removing them will mean
copying the entire file.

> >> 3. There is next a corrupt Xing (VBRI) header containing the
> >> text "Rockbox - rocks your box" Again, is this helpful? Why
> >> not put the text in the tag? I presume VBRFix will blat out
> >> the comment when you try to make the file useable.
>
> > It's a Xing header, not VBRI. What makes you think the tag is
> > corrupt? It just lacks the TOC, which is perfectly valid. The
> > text is there for the fun of it and nothing else.
>
>Additionally, the text lies outside the defined data area of
>the xing header, so it doesn't make the header invalid.

It seems I must take a closer look at this frame to see exactly what is
going on.

I am all for "fun text" (just take a look at my games! LOL) ...I just
thought it would be nicer placed where it will be read by people :)

>Regards, Jens

Cheers m8,

BC
Received on Sun Nov 6 05:12:03 2005


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