mad-user September 2004

mad-user@lists.mars.org

5 participants
4 discussions

Where the hell is definition of struct id3_file????
by tj 29 Sep '06

29 Sep '06

In trying to learn how to use libid3, since there sems to be no documentatio. I am looking at soure trying to figure out how to use it. The first problem is the practically every call uses a pointer to a "struct id3_file" . Now, the problem is that there is no definition for id3_file structure in any .h file. I finally found it in file.c, a source file. How the hell are you supposed to use it in your app when the prototype is in a package source file? Seems that something is really broken here. tj

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MAD and Jack.....
by andrew＠fnarg.demon.co.uk 08 Sep '04

08 Sep '04

Hi there, I'm writing a playout system which utilises Jack and MAD to play MP3 files. I've written a simple app which under libao (I was using this prior to Jack) will happily play any MP3 file I throw at it. However, upon adding the relevant code to make it a Jack client I've run across a problem. MAD seems to output audio at either 24bit fixed point or 16bit signed whereas Jack expects audio in 32bit floating point. Is there an easy way to make this work, am I being thick? Please help! Cheers, Andy M

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How to manipulate both V1 and V2 tags in the same file
by Cedric Tefft 07 Sep '04

07 Sep '04

I've been playing around with libid3tag 0.15.1b for a couple days now, and I'm at a loss when it comes to manipulating multiple tags in the same file. When reading a file with only one tag (either V1 or V2), reading/parsing the frames and fields works more or less as I'd expect given the API functions in id3tag.h. Where I run into trouble is when I read an MP3 file with both V1 and V2 tags. The first thing I do after opening the file is call id3_file_tag() to get a pointer to a tag. What I find confusing is that even though the tag's ID3_TAG_OPTION_ID3V1 option is set, walking the field list only gives me the frames from the V2 tag: for(i=0;i<tag->nframes;i++) { frame=tag->frames[i]; /* etc. */ } Poking around a bit in file.c it appears the id3_file structure maintains references to all of the individual tags in the file, but looking through the API functions available in id3tag.h, I don't see how to access any tag other than the primary (via the id3_file_tag() function). So my question is, how do I access the fields of a V1 tag when a file has both V1 and V2 tags? Are the V1 fields stored in the primary tag structure along with the V2 fields? If so, why can't I access them when I walk the list of the other (V2) frames? If they're stored in a tag structure other than the primary, how do I access it? Thanks, - Cedric

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Re: [mad-user] MAD and Jack.....
by jens-lippmann＠t-online.de 07 Sep '04

07 Sep '04

Hi! I'm new to the list and I'm not familiar with libmad, but have a look at this function from the madlld sample. You can easily change it to produce 32-bit floating point: float f; if (Fixed & (1<<31)) { // negative Fixed = Fixed & ((1<<31)-1); // strip sign f = -(float)Fixed / (1<<MAD_F_FRACBITS); } else { f = (float)Fixed / (1<<MAD_F_FRACBITS); } return f; hope this helps Jens /**************************************************************************** * Converts a sample from mad's fixed point number format to an unsigned * * short (16 bits). * ****************************************************************************/ static unsigned short MadFixedToUshort(mad_fixed_t Fixed) { /* A fixed point number is formed of the following bit pattern: * * SWWWFFFFFFFFFFFFFFFFFFFFFFFFFFFF * MSB LSB * S ==> Sign (0 is positive, 1 is negative) * W ==> Whole part bits * F ==> Fractional part bits * * This pattern contains MAD_F_FRACBITS fractional bits, one * should alway use this macro when working on the bits of a fixed * point number. It is not guaranteed to be constant over the * different platforms supported by libmad. * * The unsigned short value is formed by the least significant * whole part bit, followed by the 15 most significant fractional * part bits. Warning: this is a quick and dirty way to compute * the 16-bit number, madplay includes much better algorithms. */ Fixed=Fixed>>(MAD_F_FRACBITS-15); return((unsigned short)Fixed); }

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mad-user September 2004