On the 1st of May the TV streaming giant Netflix announced that it’s increasing the bitrate of some of their audio streams. We, the audio people are well acquainted with bitrate issues, so let’s reflect upon what this holds for streamed video!
So, first the primer in audio bitrate. It’s basically the universal measure in audio resolution and for lossless audio it’s calculated by this handy formula – (bit depth)*(sample rate)*(number of channels). So for redbook standard audio it’s 16*44100*2=1411.20kbps. One can then employ lossless compression to bring the bitrate down to say 850kbps, without losing any of the original data. In other words – lossless compression is just a more efficient way of expressing the same information.
With lossy compression it’s much more complicated as different compression algorithms work in different ways to strip the original material of information. The idea behind lossy compression is that the human auditory apparatus isn’t able to distinguish some audio information and thus we should be able to safely eliminate it from the recording. For example very soft sounds will be masked by louder transients, hence their loss shouldn’t be picked up by the listener.
The discussion behind lossy format bitrate was especially fiery in the early days of MP3, because back then the compression mechanics weren’t too sophisticated and just about everyone could hear the difference between every quality tier from the abysmal 64kbps to the elite 320kbps. There’s a good chance that you remember the aluminum foil crinkle sound artefact which was present in all but the highest quality MP3’s. Nowadays even the MP3 has been much improved and the most popular streaming service Spotify uses an even better .ogg file format. Even if the compression at 128kbps is noticeable when compared to the lossless source file, it’s way less annoying as when compared to the lossy music of MP3’s heyday.
What Netflix has done?
The gist of the matter is that 5.1 and Dolby Atmos material has had its maximum audio bitrate increased from 192kbps to 640kbps for 5.1 and 764kbps for Atmos. No word about stereo audio streams, so we’re presuming that these remain at 128kbps. From a purely audio perspective 128kbps doesn’t look too promising, however when one’s attention is focussed on the screen, the shortcomings of audio compression are less noticeable.
When we compare Netflix’s audio bitrate to one provided by physical media like Blu-ray, it certainly gets dwarfed. Only Dolby Digital, a movie sound standard from the late nineties compares.
|LPCM (Lossless)||Dolby Digital||Dolby Digital Plus||Dolby TrueHD (Lossless)||DTS Digital Surround||DTS-HD Master Audio (Lossless)|
|SMax. Bitrate||27.648 Mbps||640 kbps||4.736 Mbps||18.64 Mbps||1.524 Mbps||24.5 Mbps|
|Max. Channel||8 (48 kHz, 96 kHz), 6 (192 kHz)||5.1||7.1||8 (48 kHz, 96 kHz), 6 (192 kHz)||5.1||8 (48 kHz, 96 kHz), 6 (192 kHz)|
|Bits/sample||16, 20, 24||16, 24||16, 24||16, 24||16, 20, 24||16, 24|
|Sample frequency||48 kHz, 96 kHz, 192 kHz||48 kHz||48 kHz||48 kHz, 96 kHz, 192 kHz||48 kHz||48 kHz, 96 kHz, 192 kHz|
So Netflix still has room to grow in terms of audio resolution. What needs to be kept in mind is that storage space in physical media like the aforementioned Blu-ray disks is plentiful, while internet bandwidth has started to grow very recently as older telecom infrastructure gets replaced. And when given a chance, we’d expect Netflix to increase its picture quality first, as that would yield a very noticeable benefit to the largest amount of viewers.
A bitrate arms race
Will movie streamers go Pono on us and try to romance people with promises of audio bliss brought through sky high sample rates? Highly unlikely. If Neil Young couldn’t do it for audiophiles, then a picture streaming service wouldn’t bother to try it that way. Especially when the audio hardware many Netflix watchers use is hardly hi-fi.
Our VP of Strategy and Business Development Sayed Tarif comments: “I think the Netflix story is similar to the music industry Hi-res story. It is obvious that delivering sound over higher bitrates is not enough.” He then added that the hardware that does the actual playback still remains the biggest obstacle to a quality sound. Here at Sonarworks we are focused on digitally fixing the shortcomings of sound playback, which makes all music sound better and with our upcoming personalization tech we’ll make sure that the “better” works for everyone.