mad-dev May 2002

mad-dev@lists.mars.org

20 participants
15 discussions

Upsampling
by armin.gerritsen＠philips.com 30 May '02

30 May '02

Hello, Is is possible to do automatic upsampling of MP3's? I mean, if for instance a MPEG file is 32kHz, the output can be 44,1kHz anyway. Unless I missed it, I had the impression it was not possible and have to go looking for other sources. Regards, Armin

4 3

libid3tag: writing tags to files
by Sam Clegg 30 May '02

30 May '02

I am finishing of the id3 editor for xmms-mad and I am at the point where I would like to add/update tags in files. Does/will libid3tag support writing tags to a file? It looks like id3_file_update is supposed to do this but isn't implemented yet. Line 454 of file.c: /* ... */ Is this the plan (in which case I will wait (or send patches!)) or should I just write my own code that used the render functions and then somehow prepends a v2 tag and appends a v1 tag like the code in audacity? sam -- sam clegg :: samc(a)superduper.net :: http://superduper.net/ :: PGP :: D91EE369 $superduper: .signature,v 1.4 2002/04/27 11:54:02 samc Exp $

2 1

mad on arm processor -- strange problems.
by Reza Naima 30 May '02

30 May '02

I'm trying to write some mp3 playing software (www.reza.net/rio/rrr.html) for the rio receiver using the mad libraries. I've followed the example from minimad, and I've been able to make some progress, but there are some issues I'm having. First though, the system specs : Linux version 2.2.14-rmk4-mercury17-v1.01 (root(a)sticky.mock.com) (gcc version 2.95.2 19991024 (release)) #15 Sun Feb 25 19:24:49 PST 2001 Processor : ARM/VLSI arm720 rev 2 I've compiled the libs using these options : ./configure --enable-fpm=arm --host=armv4l Now, when I to decode it, the following things happen : - input callback called - error callback called (MAD_ERROR_LOSTSYNC at frame 0) * i ignore this and keep processing * This error also occurs with minimad playing - output callback is called multiple times * I get some audio out, music + loud clicks, till it runs out of data to decode - input callback is called - error callback called (MAD_ERROR_LOSTSYNC) - error callback called * the error code varies here, so far I've seen either MAD_ERROR_BADSAMPLERATE or MAD_ERROR_BADDATAPTR - i stop decoding at this point. now, as I'm also getting the MAD_ERROR_LOSTSYNC with minimad, I'm guessing (hoping) that I'm feeding some incorrect compile option to the madlibs. Any thoughts would be greatly appreciated. Reza

4 14

Decode MP3 at tx39
by davidlee 27 May '02

27 May '02

Dear All: I just do some work to make my develope board with tx3911 play MP3 with 22.05K sample rate. But when I use --downsample option to play 44.1Khz MP3, I must use another option -m, else there is terriable distortion. I wonder if somebody can give me some advise to improve the efficiency of my player(madplay). 李大冀 Email: davidlee(a)gv.com.tw

2 2

frame decoding questions
by Russell O'Connor 26 May '02

26 May '02

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 [To: mad-dev(a)lists.mars.org] I'm trying to implement better seeking in my application. First, easy question: I believe after calling mad_decode_header, the amount of (decoded) data in the next frame is: 64*MAD_NSBSAMPLES(&(sync.frame.header))*MAD_NCHANNELS(&(sync.frame.header)) Next question: after calling mad_decode_header, am I allowed to call mad_decode_frame to actually decode the frame? The idea being to seek to where I want be by calling decode_header a bunch of time till I get to where I want to be. I think decode_frame returns -1 after I call decode_header. I'm not sure if this the the behaviour to expect, or if I'm doing something wrong. - -- Russell O'Connor roconnor(a)math.berkeley.edu <http://www.math.berkeley.edu/~roconnor/> ``Later generations will regard set theory as a disease from which one has recovered.'' -- Poincare -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (SunOS) Comment: For info see http://www.gnupg.org iD8DBQE87v6KuZUa0PWVyWQRAnYWAJ9KyLO66lp5wJjSb4pKj0SOWp7tzQCcDubu mQRz82MfkI6fWF85Y97dzCw= =COB6 -----END PGP SIGNATURE-----

2 7

resample library
by Sam Clegg 16 May '02

16 May '02

I have noticed that there are many projects that reproduce the same sample conversion routines for changing sample rate / frequency / endieness / channels. Of the top of my head: esd/arts/xmms/madplay/ libaudiofile. Perhaps there is already such a library, but if not I was hoping that this could warrant the creation of a second 'companion' library to mad (libresample or something). It could also contain down mixing routines for combining channels. just a thought sam -- sam clegg :: samc(a)superduper.net :: http://superduper.net/ :: PGP :: D91EE369 $superduper: .signature,v 1.4 2002/04/27 11:54:02 samc Exp $

3 5

Equaliser style effect.. i.e visualisation.
by Thomas Rathbone 16 May '02

16 May '02

In what stage of the decoding process can i find the information I would need to create an equaliser (a frequencies bar graph) visualisation? Do I just look at the subband levels or is that totally wrong? Has anybody done this? Much thanks. Tom.

2 4

using libmad for Arm processor...
by Simone SN. Naso 15 May '02

15 May '02

Hi all, I'm trying to use libmad under WindowsCE in an ARM system (pocket PC). I've modified minimad.c so it open a file .mp3 and try to write the PCM samples in an output file. I've experienced an error when minimad read the header of the input file, but I've ingored it as Rob Leslie said in an older mail. Now the program don't give me any error, but it writes void PCM samples in the output file. Does someone know what does it mean? Note that the problem is not writing the samples to the output file: the function of libmad that decompress the .mp3 returns all 0 PCM samples!!! Another problem: I would like to write a .wav file, so I need to get various information about the file .mp3 that minimad is reading. For example, I need to know the sample frequency; in the comments of minimad.c there's written: "header->sfreq contains the sample frequency of the input file" So I've used this variable and I've discovered that header->sfreq conteined 0! Is this thing correlated with the former I've written of?

1 0

errors and MAD_RECOVERABLE()
by Thomas Rathbone 14 May '02

14 May '02

Using the high level API. In the error callback if MAD_RECOVERABLE(stream->error) returns true how do I deal with the error? Do I just report the error and return MAD_FLOW_CONTINUE? Will madlib recover the error itself or do I have to fix the error before resuming?

2 1

rio receiver replacement software
by Reza Naima 13 May '02

13 May '02

I'm currently working on an open-source re-write of the client software for the rio receiver (http://www.reza.net/rrr.html). The device is based on a linux ARM processor built by the empeg team. I've noticed the audio_empeg.c file which is probably the way I want to go, but I'm not sure what to use for documentation. I've looked at both minimad.c and madlld.c files, but I still don't have a good feel for the best way to go about implementing the code. I basically have two buffers, one with raw MP3 data, and one where I need to write the post-processed data in empeg-friendly format. Any suggestions for a good reference? Should I go the low-level or high-level route? Thanks, Reza

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mad-dev May 2002