MP3 vs. AAC

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MP3 vs. AAC: Audio Quality Comparison

MP3 Audio Compression

MP3, or MPEG Audio Layer-3, is a widely-used audio format known for its efficient compression. It uses perceptual coding techniques to discard certain audio frequencies that are less perceptible to the human ear. This compression allows for smaller file sizes while maintaining an acceptable level of audio quality.

AAC Audio Codec

AAC, or Advanced Audio Coding, is a successor to MP3 and offers improved audio quality at similar bitrates. AAC utilizes more advanced compression algorithms, including perceptual noise shaping and temporal noise shaping, resulting in better sound reproduction and higher fidelity compared to MP3.

Differences in Audio Quality

When comparing MP3 and AAC in terms of audio quality, there are several factors to consider. AAC generally provides better sound quality than MP3 at similar bitrates. This is because AAC is capable of preserving more audio details and nuances, resulting in a more accurate reproduction of the original sound.

Bitrate Efficiency

One advantage of MP3 over AAC is its superior bitrate efficiency. MP3 achieves good audio quality while keeping file sizes relatively small. This makes it suitable for applications with limited storage or low bandwidth, such as online music streaming or portable audio players.

Transparent Compression

AAC is often considered a “transparent” audio codec, meaning it can achieve audio quality indistinguishable from the original source, even at lower bitrates. This makes AAC a preferred choice for high-quality audio applications, such as digital music distribution and professional audio production.

Compatibility and Support

MP3 enjoys broad compatibility across various devices and platforms due to its widespread adoption. It is supported by virtually all audio players, software, and hardware devices. AAC, on the other hand, may require specific codecs or software support, although it has gained significant popularity and compatibility in recent years.

Application Considerations

Choosing between MP3 and AAC depends on the specific application and user preferences. If file size and compatibility are the primary concerns, MP3 may be the preferred choice. However, for applications where audio quality is paramount, such as music production or high-fidelity audio playback, AAC offers a superior option.

Transcoding and Conversion

Transcoding or converting audio files from one format to another may result in some loss of audio quality. If transcoding from MP3 to AAC, the original MP3 compression artifacts may be retained or exacerbated. It is generally recommended to use the highest-quality source file available to maintain audio fidelity.

Subjective Listening Tests

Subjective listening tests involving trained listeners have consistently shown that AAC often provides better audio quality compared to MP3 at similar bitrates. However, individual preferences can vary, and some listeners may not perceive significant differences between the two formats in certain scenarios.

Choosing the Right Format

Ultimately, the choice between MP3 and AAC depends on factors such as the intended use, available storage or bandwidth, desired audio quality, and compatibility requirements. Evaluating these factors and conducting listening tests can help determine the most suitable audio format for a specific application or use case.

Optimizing Audio Quality

To optimize audio quality, it is important to consider not only the choice of audio format but also factors such as the source recording quality, mastering techniques, and the playback equipment used. Additionally, using higher bitrates

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Should I use the MP3 or AAC codec for the .mp4 file?

We have a coding process. This process will take the original video and a couple of files from it: .m3u8 video, .mp4 video, and .mp3 audio file.

By default, we use video from our m3u8 process, which is h264 video (via libx264) with AAC audio (via libfaac).

We mainly use these videos on mobile devices (hence m3u8 files), but we also use .mp4 files for Android phones, Windows, etc. Increasingly, we also have to offer these same videos on the Internet through a flash player. or HTML5 player.

So we would like to have a better combination of audio / video codecs for all these purposes … where I am confused is what is the “standard” for an .mp4 file?

If .mp4 uses mp3 codec then it plays fine everywhere except QuickTime, in QuickTime the video plays, but there is no sound (it works fine in VLC player though).

They told me it has something to do with the way QuickTime uses file extensions to get information about the video instead of trying to get the codec data from the file. It makes some sense, if we encode the same file but use AAC for the audio codec, then it works fine in QuickTime.

So what is a “correct” or “ideal” combo audio / video codec? Is it the best and safest to use AAC (ie will it work on a wide range of devices) even if it is not a “free” codec?

AAC Audio Codec (Advanced Audio Coding)

AAC Audio Codec (Advanced Audio Coding)

AAC is a lossy audio compression method developed by MPEG Group (Moving Picture Experts Group). It was specified as a further development of MPEG-2 in the MPEG-2 standard. During development, known weaknesses and issues in the MP3 encoding process were taken into account and greatly improved.

Well, the sound quality is excellent. However, it comes at a price, and very few operators of video forums and vlogs will invest in the costs of the license. This is where open source solutions like FAAC (Free Advanced Audio Codec) become interesting. The AAC audio codec has the great advantage that it can deliver (reasonably) good stereo quality at bit rates around 64 kb.

As for the H.264 video codec, several profiles have been defined for the AAC audio codec. In this case, however, from the International Organization for Standardization, or ISO for short. Above all, they make it easier for hardware manufacturers to use this compression method. Here we will briefly introduce the most common profiles.

Low complexity profile (AAC-LC)

Designed primarily for medium to high bit rates. This profile is compatible with most AAC-compliant hardware end devices. Due to its advantages in terms of encoding and decoding efficiency and better sound quality at higher bit rates, this profile is the most common profile among all hardware manufacturers and music store providers.

Main Profile (Main AAC)

This profile is designed for low to medium bit rates. Due to its much higher encoding and decoding performance compared to AAC-LC, this profile is relatively inefficient. The sound quality at medium bit rates is better than that of the AAC-LC profile, but in no way justifies this inefficiency.

High Efficiency Profile (HE-AAC)

This profile is also designed for low to medium bit rates. However, thanks to the technical implementation of spectral band replication, or SBR for short, it offers significantly better quality at very low to medium bit rates than with the other two profiles. The high efficiency profile of the AAC audio codec is mainly used in streaming. However, at higher bit rates, the sound quality of the AAC-LC profile is better.

AAC improvements over MP3

Advanced Audio Coding is designed to be the successor to MPEG-1 Audio Layer 3, known as MP3 format, which was specified by ISO / IEC at 11172-3 (MPEG-1 Audio) and 13818-3 (MPEG-2 Audio).

Blind tests in the late 1990s showed that AAC demonstrated higher sound quality and transparency than MP3 for files encoded with the same bitrate.

The improvements include:

higher sampling frequencies (8-96 kHz) than MP3 format (16 to 48 kHz);
up to 48 channels (MP3 supports up to two channels in MPEG-1 mode and up to 5.1 channels in MPEG-2 mode);
Arbitrary bit rates and variable frame length. Standardized constant bit rate with bit deposit);
higher efficiency and simpler filter bank (instead of hybrid MP3 encoding, AAC uses pure MDCT);
higher coding efficiency for stationary signals (AAC uses a block size of 1024 or 960 samples, allowing more efficient coding of sample blocks than MP3 576);

higher coding precision for transient signals (AAC uses a block equal to 128 or 120 samples, allowing more precise coding of blocks of MP3 192 samples);
possibility of using derivatives of the Kaiser-Bessel window function to eliminate spectral dispersion at the expense of enlarging the main lobe;
much better management of audio frequencies above 16 kHz;
more flexible joint stereo (different methods can be used in different frequency ranges);
additional modules (tools) added to increase compression efficiency: TNS, Back Prediction, PNS, etc. These modules can be combined to form different encoding profiles.
In general, the AAC format allows developers more flexibility in codec design than MP3 and corrects many of the design choices made in the original MPEG-1 audio specification. This increased flexibility often leads to multiple simultaneous encoding strategies and consequently more efficient compression. However, in terms of whether AAC is better than MP3, the advantages of AAC are not entirely conclusive, and the MP3 specification, while dated, has proven surprisingly robust despite notable flaws. AAC and HE-AAC are better than MP3 at low bit rates (typically less than 128 kilobits per second). This is especially true at very low bit rates where superior stereo, pure MDCT encoding, and better transform window sizes let MP3 compete.

While the MP3 format has almost universal hardware and software support, mainly because MP3 was the format of choice during the crucial early years of music sharing / distribution over the Internet, AAC is a strong competitor due to some unwavering support from the industry.

How AAC works

AAC is a wideband audio coding algorithm that takes advantage of two main coding strategies to dramatically reduce the amount of data required to represent high-quality digital audio:

Components of the signals that are perceptually irrelevant are discarded.
Excess in the encoded audio signal is removed.
The actual encoding process consists of the following steps:

The signal is converted from the time domain to the frequency domain using the Forward Modified Discrete Cosine Transform (MDCT). This is done using filter banks that take an adequate number of time samples and convert them to frequency samples.
The signal in the frequency domain is quantized based on a psychoacoustic model and encoded.
Internal error correction codes are added.
The signal is stored or transmitted.
To avoid corrupted samples, a modern implementation of the luhn mod N formula is applied to each frame.
The MPEG-4 audio standard does not define a single or small set of highly efficient compression schemes, but rather a complex set of tools to perform a wide range of bitrate encoding operations, from low speech to audio encoding. high quality and musical synthesis.

The ‘MPEG-4 family audio coding algorithm covers the range from low speech coding bit rate (up to 2 kbit / s) to high quality audio coding (at 64 kbit / s per channel and higher).
AAC offers sample rates between 8 kHz and 96 kHz and any number of channels between 1 and 48.
In contrast to MP3’s hybrid filter bank, AAC uses Modified Discrete Cosine Transform (MDCT) in conjunction with increasing window lengths of 1024 or 960 points.