mad-dev October 2001

mad-dev@lists.mars.org

7 participants
7 discussions

(no subject)
by Rene Rebe 03 Nov '01

03 Nov '01

Hi. > I was looking through the MAD examples (minimad and madplay) in order for > me to integrate MAD into Apollo. It became apparent pretty quickly > that this is no easy task, with just one of the files for the madplay > example touching 2000 lines of compact, fairly complex code. That combined > with no documentation easily destroyed most of my motivation. > > I wondered if anybody has written a fairly decoupled C++ wrapper class. It > doesn't have to be quite: A C+… [View More]

3 3

MAD 0.14.1b available
by Rob Leslie 23 Oct '01

23 Oct '01

MAD version 0.14.1b is now available. Since the release of 0.14.0b, a number of issues were immediately raised that warrant a new release. Directly from the CHANGES file: - Updated config.guess and config.sub to latest upstream versions. - Enabled libtool versioning rather than release numbering. - Renamed `libid3' to `libid3tag' and enabled installation as a separate library. - Enabled the plug-in for Winamp to use libid3tag. - Fixed a NetBSD compatibility issue in audio_sun. … [View More]

1 0

Some information about programming with MAD (in synchronous mode)
by Joe Drew 22 Oct '01

22 Oct '01

As the author of mpg321, I too faced the problem of MAD not being documented. However, in looking at minimad.c, and re-writing mpg321 to use MAD, I came to understand it better. Here's some information which will help anybody start out with MAD: First, some basic information. MAD operates with callbacks for functions. Each of these functions is expected to return type enum mad_flow; this allows you to control the decoding process. MAD always outputs 32-bit (well, mad_fixed_t) little-endian … [View More]data. Take this into account when outputting samples to the sound card. Related to the above, since MAD outputs type mad_fixed_t, unless you can output with 32-bit accuracy (most sound cards can't), you will have to quantize, round, dither, etc these samples to 16-bit (or whatever you need.) While there is a sample routine in minimad.c, if you want good quality you'll either want to roll your own or take a look in madplay's sources. Integral to understanding MAD: MAD is a decoding library only. You handle input and output; you're responsible for fast-forwarding and rewinding, if you want that type of functionality. All that MAD will do is take input from you, decode the MPEG frames, give you some information about them, and give you the decoded PCM data. Now, the nitty-gritty information. First, you need a mad_decoder struct. This holds all information about how you want your stream decoded, such as input/output functions, error handling functions, etc. mad_decoder_init() sets this structure up for you. struct mad_decoder decoder; struct my_playbuf playbuf; mad_decoder_init(&decoder, &playbuf, input_func, header_func, /*filter*/ 0, output_func, /*error*/ 0, /* message */ 0); In this example, the function called to get more data is set to input_func, the function called after MPEG headers have been decoded is header_func, the function called after all sound data has been decoded to PCM (for output) is output_func, and the filter, error, and message functions are unset. Now, MAD runs in a constant decoding loop. It runs something along the following lines: if I'm out of data call input_func if input_func says there's no more data, quit decode the header and call header_func decode the mpeg audio data call the filter function call the output function loop Now, this is an oversimplification obviously. The important thing to realise is that at every step of the process you can tell MAD what to do. Since all of these functions return enum mad_flow, you can tell MAD to do any of the following: enum mad_flow { MAD_FLOW_CONTINUE = 0x0000, /* Keep decoding this stream */ MAD_FLOW_STOP = 0x0010, /* Stop decoding this stream, but exit normally */ MAD_FLOW_BREAK = 0x0011, /* Stop decoding this stream, and exit with an error */ MAD_FLOW_IGNORE = 0x0020 /* Don't decode this frame, but continue afterwards */ }; Most of the time you'll probably want to return MAD_FLOW_CONTINUE. In every case, you'll have to return one of these values from the functions you define. This is the definition of each of the functions: enum mad_flow (*input_func)(void *, struct mad_stream *); enum mad_flow (*header_func)(void *, struct mad_header const *); enum mad_flow (*filter_func)(void *, struct mad_stream const *, struct mad_frame *); enum mad_flow (*output_func)(void *, struct mad_header const *, struct mad_pcm *); enum mad_flow (*error_func)(void *, struct mad_stream *, struct mad_frame *); enum mad_flow (*message_func)(void *, void *, unsigned int *); In each of these functions the void* pointer passed to the function is your "playbuf" structure. This can hold whatever you want - for example, song title, length, number of frames - just remember to re-cast it to the type you've defined. input_func takes a mad_stream pointer. Most of the time what you'll want to do is something along the lines of the following: if (more_data_available) buffer = refill_buffer(); mad_stream_buffer(stream, buffer, length_of_buffer); return MAD_FLOW_CONTINUE; else return MAD_FLOW_STOP; (On many systems you'll want to use mmap() for this.) header_func takes a mad_header pointer. This contains most of the important information about a given frame; in constant bitrate files, it can contain most of the important information about the stream. It will give you the length of that frame, using mad_timer_t; the audio layer; extension; bitrate... the list is long. Read frame.h or mad.h in the frame.h area for more information. Again, return MAD_FLOW_{CONTINUE,STOP,BREAK} depending on outside conditions. The only other function I have firsthand information on is output_func; in this case, you are given a pointer to struct mad_pcm. This gives you the sampling rate, number of channels, and number of samples per channel; doing something like the following should work: mad_fixed_t *left_channel = pcm->samples[0], *right_channel = pcm->samples[1]; int nsamples = pcm->length; signed int sample; unsigned char * buffer = some_buffer; unsigned char * ptr = buffer; while (nsamples--) { sample = (signed int) do_downsample(*left_ch++) *ptr++ = (unsigned char) (sample >> 0); *ptr++ = (unsigned char) (sample >> 8); sample = (signed int) do_downsample(*right_ch++) *ptr++ = (unsigned char) (sample >> 0); *ptr++ = (unsigned char) (sample >> 8); } output buffer to device. Be sure to handle the big-endian case (autoconf can test for this), and also the mono (1 channel) case. See mad.c in mpg321, at the end of the file, for an example. Information on the other (error, filter, message) functions would be appreciated, though I think in knowing this information anyone should be able to puzzle it out. Now that the decoder is set up with all these callback functions, you call mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC); and then mad_decoder_finish(&decoder); Once you've called mad_decoder_finish, you can re-use the decoder struct, if you're, for example, within a playlist. Incidentally, all MAD structures have similar mad_(whatever)_init and mad_(whatever)_finish functions. I hope this helps people get their feet wet with MAD. Read the source, and particularly mad.h - there are a lot of things there you might not expect. Rob has done a good job in making MAD a complete solution. :) -- Joe Drew <hoserhead(a)woot.net> <drew(a)debian.org> Please encrypt email sent to me. [View Less]

3 2

C++ wrapper?
by Marius Sundbakken 22 Oct '01

22 Oct '01

I was looking through the MAD examples (minimad and madplay) in order for me to integrate MAD into Apollo. It became apparent pretty quickly that this is no easy task, with just one of the files for the madplay example touching 2000 lines of compact, fairly complex code. That combined with no documentation easily destroyed most of my motivation. I wondered if anybody has written a fairly decoupled C++ wrapper class. It doesn't have to be quite: MP3File m("my_song.mp3"); m.play(); but at … [View More]

3 6

MAD 0.14.0b available
by Rob Leslie 22 Oct '01

22 Oct '01

MAD version 0.14.0b is now available. Highlights of this release include: - a new ID3 tag manipulation library implementation - a new dithering algorithm for (hopefully) even better sound quality - keyboard controls for `madplay' (see the man page for details) - a fix for `madplay' segfaults on files that are a multiple of 4K - improved code portability, and new MSVC++ project files - other various small code improvements The new ID3 tag manipulation library is the most … [View More]

2 2

Credit where credit is due
by Rob Leslie 19 Oct '01

19 Oct '01

It has come to my attention that I have overlooked giving proper credit to folks who suggested some of the improvements in the latest release of MAD. Such was certainly not my intention. Given the time elapsed since the previous release it seems I may have forgotten to add a few lines to the CREDITS file. If anyone here believes they should be given credit for something in the latest release of MAD and I didn't acknowledge it in the CREDITS file, would you kindly send me a private note to … [View More]

1 0

hang in huff code
by Brett Paterson 18 Oct '01

18 Oct '01

Posted with wrong from address.. here it is again. Hi im new to the list. Im trying to decode some data using the low level api, I want to decode it a frame at a time , but currently im just trying to do something simple, give it 8k of data and have it call decode without hanging. in is a pointer to the data, I just put 8192 in for the hell of it. The 8k of data is valid mpeg data and I can decode it fine with my own fpu based mp3 code. I tried this mad_stream_init(&stream); … [View More]

3 5

2025

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

mad-dev October 2001