mad-dev July 2003

mad-dev@lists.mars.org

16 participants
17 discussions

Quantizing mad_fixed_t?
by Arve Knudsen 20 Jul '03

20 Jul '03

I see that the algorithm for 32 bit output in madplay quantizes to 24 bit; I'm a little daft when it comes to fixed point representations, but why are some of the fractional bits discarded even when you're outputting in full 32 bit? There's also one more thing I don't understand; the original sign bit of the fixed point number isn't kept (as far as I can see), instead the least significant whole part bit occupies the sign position. Does this whole part bit represent the sign (a little confused here)? Regards Arve Knudsen

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MAD Documentation
by Zeon 16 Jul '03

16 Jul '03

Hello, I'm looking for MAD documentation. Thanks

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samplerate/channels computation on layer 2
by Patrick Cernko 10 Jul '03

10 Jul '03

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, I'm one of the developers of NMM (thanks for your link to use on your Website). We are using libmad to decode MPEG Audio Layer 2 as received by Digital Video Broadcast (DVB) via satelite. After remuxing the received MPEG transport stream to a MPEG 2 PES stream (first part: DVBReadNode) it is demultiplexed into its audio and video parts by our MPEG Demultiplexer Node (= demuxer unit). The resulting MPEG Audio part is MPEG Audio layer 2 with 48000 Hz sample rate (at least we did not found any other one yet) and one ore 2 channels. It is decoded by the MPEGAudioDecodeNode based on libmad version 0.14.2b. The code was inspired by the minimad example from your distribution although we had do make many changes, e.g. unlooping the while loop to process the incoming buffers or computing timestamps for the decoded audio buffers for later syncronisation with the video frames. Now back to my problem. I discovered, that some few times, the mad_pcm struct seems to contain invalid values for samplerate and number of channels. Although the mad_header struct in the mad_frame says, that the frame has 48000 Hz and 1 channel, in the mad_pcm struct, the values are 24000 Hz and 2 channels (see: the total number of samples is 96000 in both cases). I already tried the newer version 0.15 of the mad library, but I get the same effects. We also have mad a "simulation", where we use a recorded DVB-Stream. The effect apears here also indeterministically. Also playing the demulitplexed audio stream is affected. The "accident" occures not so often and most times, it is not reproduceable directly after it occured, except if the application is left running. When the app is left running we can reproduce it a few times and after 4-5 tries, the decoder gets it right. We also tried not to use the values from the mad_pcm struct but the ones from the mad_header struct, but as we heard, the decoded audio data was also affected (or wrong interleaved). Can you give me some hints where I can search for the error or do you think, this is a bug in the library perhaps? I would like to test it also with the current development library. Do you have something like anonymous CVS access? CU/all P.S.: If you want to see our implementation, you can download the latest NMM release. The Code in this release is (at least for the MPEGAudioDecodeNode) nearly identical with our current CVS head! - -- Patrick Cernko | mailto:errror@errror.de | http://www.errror.de Quote of the Week: "Is net scheen, das Bild, awwer einmalisch!" (Markus Sand) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.0 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQE/DatgB6g1EUxThvcRAg0OAKCsYBqKTWuN2suqQlIlVxszLavSPQCfYxrT TMXLriDskDnecWV4KNCcH8M= =LvIq -----END PGP SIGNATURE-----

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mad_frame subbands and filtering
by Bill Zissimopoulos 08 Jul '03

08 Jul '03

I need to process frame subbands before synthesis occurs. Libmad conveniently makes them available through its filtering feature. However the information around filtering is rather limited. I have studied the source code in filter.c and (think that I) have read all the relevant articles in this list, so I understand the basics, however I do have a few more questions: 1. What are the units and range of values for each subband? Must these values be scaled before they can be used? [I saw in a list article that subband values range from -MAD_F_ONE to MAD_F_ONE. Have these values been scaled?] 2. What are the frequency ranges that each subband covers? Many thanks. Bill

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question about libmad install
by Shiming Dong 06 Jul '03

06 Jul '03

Hi there: I downloaded the source code for libmad and try to install it on Windows. But I don't know how to install it, do I need to write a make file ? I have no idea at all. From the document, it said I can use either MSVC++ or cygwin. But there is no readme file for how to install using MSVC++. I installed cygwin, but I don't know how to use it to install? Sorry for my questions, but I'm a beginer and I really have no idea. If anyone could help me, I'd appreciate it very much. Thank you! shiming --------------------------------- Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month!

2 1

mad ogg support
by Joe Drew 03 Jul '03

03 Jul '03

Hi Rob, I remember you mentioning that you might implement a sort of mad-ogg which was a integer-only ogg vorbis decoder, but you were stymied by the lack of a proper specification for the ogg vorbis format. Now that Tremor has been released, do you still plan on making such a project? Thanks, Joe

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Crosscompiling for ARM - Zaurus
by Dave 03 Jul '03

03 Jul '03

Hi I've Successfully compiled madplay and it's libs for the Zaurus. Everything works. I used the following options for configure: CC=/usr/local/Embedix/tools/bin/arm-linux-gcc \ RANLIB=/usr/local/Embedix/tools/bin/arm-linux-ranlib \ ./configure --host=arm-linux \ --enable-speed \ --enable-fpm=arm \ --libdir=/opt/Qtopia/sharp/lib \ --includedir=/opt/Qtopia/sharp/include The playback sounds great. The only problem I've got is occasionally "skipping" which I'm assuming are some sort of buffering problem. The skips only occur when I run other apps while playing an MP3. They occur more often if the MP3 file is stored on an SD card or fetched from an SMB mounted file system. I haven't yet taken a good look at how madplay reads and buffers the data. I originally built it with mmap. After thinking about it - if my understanding of mmap is correct - it makes little sense on a device like the Zaurus. I rebuilt madplay without mmap (is the correct way to do this to edit config.h ?) and the skipping remains. So it seems that mmap had little effect. If mmap works on the Zaurus - when it's enabled madplay will request to have the full MP3 file "mapped" into memory to avoid disk reads while playing it (is this correct?). On the Zaurus, the MP3 will already be stored in memory, and mmap would just copy it from one chunk of memory to another. Perhaps this would save the time it take to execute the filesystem code but it would chew up memory on a limited device. Buffering - I don't know how the buffering in madplay works. I assume that buffering would be better for the Zaurus. Is madplay meant to be a robust generic MP3 player or is just to demonstrate how to use libmad? Finally, are there any other config options I should try? I'm not familiar with the ARM family of processors - I've noticed other posts that specify a specific arm chip in the config options. How about other options for libmad/madplay? Is there a way to get configure to tell you the full list of options? I tried --help but people here are mentioning options that aren't shown. I'm impressed with the work thats been done on MAD - it compiled and worked right out of the box and sounds great. The only trouble I had was figuring out how to cross compile it, and those questions were answered right here in other posts. Thanks in advance for any help offered. Dave ---------------------------------------------------------------- Dave Belser (mad(a)newww.com)

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mad-dev July 2003