Intermediate File Format for New Media Producers: MP2

mp2-file If you are in the audio production business or involved in some sort of collaborative Podcast effort, moving large lossless audio files to and from various locations can be challenging.

Slow internet speeds, Hotel WiFi, and server bottlenecks have the potential to cripple efficient file management and ultimately impede timely delivery. And let’s not forget how quickly drive space can diminish when storing WAV and/or AIFF files for archival purposes.

The Requirements for a Suitable Intermediate

From the perspective of a Spoken Word New Media Producer, there are two requirements for Intermediate files: Size Reduction and Retention of Fidelity. The benefits of file size reduction are obvious. File transfers originating from locations with less than ideal connectivity would be much more efficient, and the consumption of local or remote disk/server space would be minimized. The key here is to use a flexible lossy codec that will reduce file sizes AND hold up well throughout various stages of encoding and decoding.

Consider the possible benefits of the following client/producer relationship: A client converts (encodes) lossless files to lossy and delivers the files to the producer via FTP, DropBox, etc. The Producer would then decode the files back to their original format in preparation for post production.

When the work is completed, the distribution file is created and delivered (in most cases) as an MP3. Finally with a bit of ingenuity, the producer can determine what needs to be retained for archival purposes, and convert these files back to the intermediate format for long term storage.

How about this scenario: Podcast Producer A is located in L.A.. Producer B is located in NYC. Producer B handles the audio post for a double-ender that will consist of 2 individual WAV files recorded locally at each location.

DA

Upon completion of a session, the person in L.A must send the NY based audio producer a copy of the recorded lossless audio. The weekly published program typically runs upwards of 60 minutes. Needless to say the lossless files will be huge. Let’s hope the sender is not in a Hotel room or at Starbucks.

The good news is such a codec exists …

MPEG 1 Layer II (commonly referred to as MP2 with an .mp2 file extension) is in fact a lossy “perceptual” codec. What makes it so unique (by design) is the format’s ability to limit the introduction of artifacts throughout various stages of encoding and decoding. And get this – MP2’s check in at about 1/5th the size of a lossless source. For example a 30 minute (16 bit/44.1kHz) Stereo WAV file currently residing on my desktop is 323.5 megabytes. It’s MP2 counterpart is 58.7 megabytes.

Public Radio

If you look into the file submission requirements over at PRX (The Public Radio Exchange) and NPR (see requirements), you will notice MP2 audio files are what they ask for.

In fact during the early days of IT Conversations, founder and Executive Director Doug Kaye implemented the use of MP2 audio files as intermediates throughout the entire network based on recommendations by some of the most prominent engineers in the Public Radio space. We expected our show producers and content providers to convert their audio files to MP2 prior to submission to our servers using third party software applications.

Eventually a proprietary piece of software (encoder/uploader) was developed and distributed to our affilates. The server side MP2’s were downloaded by our audio engineers, decoded to lossless, produced, and then sent back up to the network as MP2 in preparation for server side distribution encoding (MP3).

From a personal perspective I was so impressed with the codec’s performance, I immediatly began to ask my clients to submit MP2 audio files to me, and I’ve never looked back. I have never experienced a noticeable degradation of audio quality when converting a client’s MP2 back to WAV in preparation for post.

Storage

In my view it’s always a good idea to have unfettered access to all previously produced project files. Besides produced masters, let’s not forget the accumulation of individual project assets that were edited, saved, and mixed in post.

On average my project folders that include audio assets for a 30 minute program may consume upwards of 3 Gigabytes of storage space. Needless to say an efficient method of storage is imperative.

Fidelity Retention

If you are concerned about the possibility of audio quality degradation due to compression artifacts, well that’s understandable. In certain instances accessability to raw, uncompressed audio will be more suitable. However I am convinced that you will be impressed with how well MP2 audio files hold up throughout various workflows.

In fact try this: (Suggested encoders listed below)

Convert a stereo WAV file to stereo MP2 (256 kbps). Compare the file sizes. Listen to the MP2 and assess fidelity retention. Then convert the stereo MP2 directly to stereo MP3 (128 kbps). Listen for any indication of noticeable artifacts.

Let me know what you think …

My recommendation would be to first experiment with converting a few of your completed project assets to MP2 in preparation for storage. I’ve found that I rarely need to dig back into old work. I have on a few occasions, and the decoded MP2’s were perfectly fine. Note that I always save a copy of the produced lossless master.

Specifications and Software

The requirements for mono and stereo MP2 files:

Stereo: 256 kbps, 16 bit, 44.1kHz
Mono: 128 kbps, 16 bit, 44.1kHz

There are many audio applications that support MP2 encoding. Since I have limited exposure to Windows based software, the scope of my awareness is narrow. I do know that Adobe Audition supports the format. In the past I’ve heard that dBPowerAmp is a suitable option.

On the Mac side, besides the cross platform Audition – there is a handy utility on the Mac App Store called Audio-Converter. It’s practically free, priced at $0.99. File encoding is also supported in FFmpeg either from the Command Line or through various third party front ends.

Here is the syntax (stereo, then mono) for Command Line use on a Mac. The converted file will land on your Desktop, named Output.mp2:

ffmpeg -i yourInputFile.wav -acodec mp2 -ab 256k ~/Desktop/Output.mp2

ffmpeg -i yourInputFile.wav -acodec mp2 -ab 128k ~/Desktop/Output.mp2

Here’s a good place to download pre-compiled FFmpeg binaries.

Many modern media applications support native playback of MP2 audio files, including iTunes and Quicktime.

In Conclusion

If you are in the business of moving around large Spoken Word audio files, or if you are struggling with disk space consumption issues, the use of MP2 audio files as intermediates is a worthy solution.

-paul.

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2 thoughts on “Intermediate File Format for New Media Producers: MP2

  1. Thanks for this Paul. I had forgotten about MP2 encoding. You’re right we did use that during the IT Conversations days. And yes my audio project folders seems to keep getting larger and larger. I’m going to do some comparisons as you say and see if I get my clients to do the conversion. Great insights as usual from you! Thank you for putting all this together so nicely.

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