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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?

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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.