I am looking for some general advice about the mp3 format before I start a small project to make sure I am not on a wild-goose chase.
My understanding of the internals of the mp3 format is minimal. Ideally, I am looking for a library that would abstract those details away. I would prefer to use Python (but could be convinced otherwise).
I would like to modify a set of mp3 files in a fairly simple way. I am not so much interested in the ID3 tags but in the audio itself. I want to be able to delete sections (e.g. drop 10 seconds from the 3rd minute), and insert sections (e.g. add credits to the end.)
My understanding is that the mp3 format is lossy, and so decoding it to (for example) PCM format, making the modifications, and then encoding it again to MP3 will lower the audio quality. (I would love to hear that I am wrong.)
I conjecture that if I stay in mp3 format, there will be some sort of minimum frame or packet-size to deal with, so the granularity of the operations may be coarser. I can live with that, as long as I get an accuracy of within a couple of seconds.
I have looked at PyMedia, but it requires me to migrate to PCM to process the data. Similarly, LAME wants to help me encode, but not access the data in place. I have seen several other libraries that only deal with the ID3 tags.
Can anyone recommend a Python MP3 library? Alternatively, can you disabuse me of my assumption that going to PCM and back is bad and avoidable?
If you want to do things low-level, use pymad. It turns MP3s into a buffer of sample data.
If you want something a little higher-level, use the Echo Nest Remix API (disclosure: I wrote part of it for my dayjob). It includes a few examples. If you look at the cowbell example (i.e., MoreCowbell.dj), you'll see a fork of pymad that gives you a NumPy array instead of a buffer. That datatype makes it easier to slice out sections and do math on them.
I got three quality answers, and I thank you all for them. I haven't chosen any as the accepted answer, because each addressed one aspect, so I wanted to write a summary.
Do you need to work in MP3?
Transcoding to PCM and back to MP3 is unlikely to result in a drop in quality.
Don't optimise audio-quality prematurely; test it with a simple prototype and listen to it.
Working in MP3
Wikipedia has a summary of the MP3 File Format.
MP3 frames are short (1152 samples, or just a few milliseconds) allowing for moderate precision at that level.
However, Wikipedia warns that "Frames are not independent items ("byte reservoir") and therefore cannot be extracted on arbitrary frame boundaries."
Existing libraries are unlikely to be of assistance, if I really want to avoid decoding.
Working in PCM
There are several libraries at this level:
LAME (latest release: October 2017)
PyMedia (latest release: February 2006)
PyMad (Linux only? Decoder only? Latest release: January 2007)
Working at a higher level
Echo Nest Remix API (Mac or Linux only, at the moment) is an API to a web-service that supports quite sophisticated operations (e.g. finding the locations of music beats and tempo, etc.)
mp3DirectCut (Windows only) is a GUI that apparently performs the operations I want, but as an app. It is not open-source. (I tried to run it, got an Access Denied installer error, and didn't follow up. A GUI isn't suitably for me, as I want to repeatedly run these operations on a changing library of files.)
My plan is now to start out in PyMedia, using PCM.
Mp3 is lossy, but it is lossy in a very specific way. The algorithms used as designed to discard certain parts of the audio which your ears are unable to hear (or are very difficult to hear). Re-doing the compression process at the same level of compression over and over is likely to yield nearly identical results for a given piece of audio. However, some additional losses may slowly accumulate. If you're going to be modifying files a lot, this might be a bad idea. It would also be a bad idea if you were concerned about quality, but then using MP3 if you are concerned about quality is a bad idea over all.
You could construct a test using an encoder and a decoder to re-encode a few different mp3 files a few times and watch how they change, this could help you determine the rate of deterioration and figure out if it is acceptable to you. Sounds like you have libraries you could use to run this simple test already.
MP3 files are composed of "frames" of audio and so it should be possible, with some effort, to remove entire frames with minimal processing (remove the frame, update some minor details in the file header). I believe frames are pretty short (a few milliseconds each) which would give the precision you're looking for. So doing some reading on the MP3 File Format should give you enough information to code your own python library to do this. This is a fair bit different than traditional "audio processing" (since you don't care about precision) and so you're unlikely to find an existing library that does this. Most, as you've found, will decompress the audio first so you can have complete fine-grained control.
Not a direct answer to your needs, but check the mp3DirectCut software that does what you want (as a GUI app). I think that the source code is available, so even if you don't find a library, you could build one of your own, or build a python extension using code from mp3DirectCut.
As for removing or extracting mp3 segments from an mp3 file while staying in the MP3 domain (that is, without conversion to PCM format and back), there is also the open source package PyMp3Cut.
As for splicing MP3 files together (adding e.g. 'Credits' to the end or beginning of an mp3 file) I've found you can simply concatenate the MP3 files providing that the files have the same sampling rate (e.g. 44.1khz) and the same number of channels (e.g. both are stereo or both are mono).
Related
I want to make software for displaying PIP(Picture in Picture) of 2 video streams. How can i know, pyglet allows play video only from file source.
May be i decide to use wrong lib (pyglet), please, advice what lib is bettor for my goals.
I'm also will be appreciated if you advice some books or articles connected with generating video streams.
Thank you!
Pyglet is fully capable of playing video, however, as you said, I do not think it is capable of streaming video. A much more popular library for this kind of program would be GStreamer. It offers much more functionality, and it can be extended with plugins. Here is a Wikipedia page for it, and here is the official website. If you look at the features page, you will see this:
container formats: asf, avi, 3gp/mp4/mov, flv, mpeg-ps/ts, mkv/webm, mxf, ogg
streaming: http, mms, rtsp
codecs: FFmpeg, various codec libraries, 3rd party codec packs
metadata: native container formats with a common mapping between them
video: various colorspaces, support for progressive and interlaced video
audio: integer and float audio in various bit depths and multichannel configurations
So, it seems perfect for what you want to do (The bold bullet points are the ones I thought would interest you most).
Luckily GStreamer has bindings for Python.
Another library I have found, which you could use for the encoding part and all under-the-hood part is PyMedia. Maybe that would be something of interest too. However note that you do not need to use it as GStreamer can do everything that PyMedia can. I just put it in, incase you wanted to take a look at it, for future use perhaps.
Good luck.
I'd like to seperate the channels of a mp3 file in Python and save it in two other files.
Does anybody know a library for this.
Thanks in advance.
I assume you want to split the channels losslessly, without decoding MP3 and re-encoding it - otherwise you would not have mentioned MP3 at all and would have easily found many tools like Audacity to do that.
There are 4 channel modes of MP3 frames - this means 4 types of MP3 files: simple stereo, joint-stereo, dual-channel, mono. joint-stereo files can't be split without loss. mono files doesn't need splitting. The rest: stereo and dual-channel, consists of less than 0.1% of all MP3 files, technically can be split into 2 files, each for a channel, without loss. However there is not any tool on the Internet to do that - not any command line tool nor any GUI tool, because few need the function.
There are not any python library for you neither. Most libraries abstracted MP3 files into a common audio which you can manipulate, after decoding. pymad is the only one specific to MP3 file, and it can tell if a file is using any of the 4 channel modes, but does not offer to extract a channel without decoding it. If you write a new tool, you will have to work on raw MP3 files or produce a library for it.
And it is not easy to write a tool or library for it. It's one stream with 2 channels and not two streams interleaved on a frame level. You cannot simply work on MP3 frames, drop some frames, keep others, and manage to extract a channel out that way. It's a task for a professional, and perhaps best happen in a decoder project (like lame or libmad) and not in a file manipulation project (like mp3info or the python eyeD3). In other words, this feature is likely written in C, not python.
Implementaiton Note:
The task to build such a tool thus suits well for a computer science C-programming language course project:
1. it takes a lot of time to do;
2. it requires every skill learned from C programming course;
3. it can get wrong easily;
4. it is likely built on the work of other projects, a lesson of adaptating existing work;
5. is a damn-hard endeavor that no-one did before and thus very rewarding
6. perhaps can be done in 300 difficult lines of code instead of bloated simple Visual Basic code, thus is a good lession of modesty and quality;
7. and finally: nobody is waiting in an hurry for a working implementation.
All condition fits perfectly for a C-programming course project.
Implementation Note 2:
some bit-rates are only possible in mono mode (80kbps), and some bit-rates are only possible in stereo mode (e.g. 320kpbs). Luckily this does not present a problem in this task, because all dual-mp3 bit-rate can be mapped into a fitting mono-mp3 bit-rate -- but not vice versa!
I have a shoutcat radio station and now want to build a player for it. I know how to "get" thet stream from the server, thanks a lot to bobince , but I am not sure how to convert that stream into playable samples. How is it done?
Shoutcast streams are typically (but not always) MP3. To get playable samples, you have to decode the stream's MP3 data.
Have you seen the resource at http://codeboje.de/playing-mp3-stream-python/? Looks like a simple solution, but requires an awful lot of libraries.
There are quite a few possibilities for MP3 decoding under Python. PyMedia is one I've had some success with in the past (but for which development seems to have stopped). It's not just an MP3 decoder though, but a playback interface with support for many audio and video formats via ffmpeg. There's also pyffmpeg which seems to have come back to life recently (haven't tried it yet).
Then there's PyGame can also play MP3, though this is a pretty small part of what it does. pymad is more lightweight possibility, being a direct interface to the libmad decoder library. And then there's always the possibility of handing the task off to an external multimedia library such as DirectShow, or GStreamer (via gst-python)...
Well, from what I can read on python, try this page. If that doesn't work, try the PythonInMusic article on the python wiki.
I am looking for a python package or library that will allow me to programmatically output a file format (e.g. MIDI) that can be read by audio/sound processing programs, like LogicPro or iDrum. What are the best options for this?
A large number of possibilities are listed here, especially under the "Midi Mania" header. For your requirements, and the various packages' descriptions, it seems to me that pythonmidi might suit you best, but I have no first-hand experience with it.
I'm looking for a cat for aac music files (the stuff iTunes uses).
Use Case: My father in law will not touch computers except for audiobooks he downloads to his iPod. I have taught him some iTunes (Windows) basics, but his library is a mess. It turns out, that iTunes is optimized for listening to podcasts and random songs from your library, not for audiobooks.
I would like to write a script (preferably python, but comfortable with other stuff too) to import his audiobook cds in a sane fashion, combining the tracks of each cd into a bookmarkable aac file (.m4b?) and then adding that to iTunes so it shows up in the audiobooks section.
I have figured out how to talk to iTunes (there is a COM interface in Windows, look for the iTunes SDK). Using that interface, I can use iTunes to rip the CD to aac format. It's the actual concatenation of the aac files I'm having trouble with. Can't find the right stuff on the net...
I created a freeware program called "Chapter and Verse" to concatenate m4a (AAC) files into a single m4b audiobook file with chapter marks and metadata.
If you have already ripped the CD's to AAC using itunes (which you say you have) then the rest is easy with my software. I wrote it for this exact reason and scenario. You can download it from www.lodensoftware.com
After trying to work with SlideShow Assembler, the QT SDK and a bunch of other command line tools, I ended up building my own application based on the publicly available MP4v2 library. The concatenating of files and adding of chapters is done using the MP4v2 library.
There are quite a few nuances in building an audiobook properly formatted for the iPod. The information is hard to find. Working with Apple documentation and open libraries has its own challenges as well.
Best of Luck.
Not programming related (well, kinda.)
iTunes already has functionality to rip as a single track (e.g. an audiobook.) Check this out: http://www.ehow.com/how_2108906_merge-cd-single-track-itunes.html
That fixes your immediate problem, but I guess people can keep discussing how to do it programatically.
The most powerful Python audio manipulation module out there seems to be Python Audio Tools. The download comes with CLI tools that would probably do everything you'd want to do, even ripping, so you can even get by with shell scripting the whole thing. The module itself is also pretty powerful and has a handy set of functions to manipulate audio files. If you want to stick with writing everything in python, you can possibly learn enough to do what you want to do after studying their CLI source code. Specifically they have a tool that just does audio file cat in any codec. (They do depend on FAAC/FAAD2 for AAC support, but that'd be true for every library you'll find)
I haven't seen an aac codec library for python, but you could use wav files as an intermediary format.
You can pull the tracks off the cd as wav files, and then use the wave module to concatenate them into one large file, which could then be converted by itunes to aac. This may increase your processing time considerably because of the size of the data, but it would be fairly easy, and you don't need any external libraries.