H3XED
Web and Internet   Browse Topics
YouTube Audio Quality Bitrate Used For 360p, 480p, 720p, 1080p, 1440p, & Up

YouTube Audio Quality Bitrate Used For 360p, 480p, 720p, 1080p, 1440p, & Up

Posted Nov 20, 2014 by Nick Vogt
YouTube streams video and audio separately and the website player combines them on the fly. Due to this, the audio bitrate is no longer affected by the video quality selected. In most cases, the audio you hear while watching a YouTube video is approximately 126 kbps AAC (MPEG-4 audio in an M4A container). Changing the video quality will not impact the audio stream that is playing.

126 kbps might sound like a low bitrate, but the compression YouTube uses is very good. I compared it to a 192 kbps version and had a hard time telling the difference (two audio streams playing in tandem <audio> elements with JavaScript flipping between them seamlessly).


Testing Method


I created test videos with 320 kbps and 256 kbps AAC audio at three resolutions: 3840x2160 (2160p), 1280x720 (720p), and 640x360 (360p). After uploading them to YouTube and allowing them time to process, I analyzed the network traffic during playback to determine the size of the audio stream YouTube was using.

At all resolutions, from 144p to 2160p, I found that YouTube did not change the audio stream that was playing. I tested it both in the embed iframe and on the YouTube website, in both Chrome and Firefox (HTML5 and Flash players).

I was able to determine the exact size of the audio stream in bytes, which then leads to an easy kbps calculation with the length in seconds of the video (or average kbps if VBR). For more information on how I determined this through network traffic, please see this post. My test videos had approximately 126.3 kbps.

To make sure YouTube doesn't give special treatment to big name artists, I also tested two 1080p music videos from YouTube's trending page. Here is the raw data that I was able to extract from the network traffic:

http://www.youtube.com/watch?v=e-ORhEE9VVg
272 seconds long
4,374,789 bytes total audio file size
16,083.8 bytes/second
128,670.3 bits/second
125.7 kbps

http://www.youtube.com/watch?v=Ezc4HdLGxg4
283 seconds long
4,558,921 bytes total audio file size
16,109.3 bytes/second
128,874.1 bits/second
125.9 kbps

No real difference in kbps here. Still around 126 kbps.


Listening Test


I did an additional unscientific listening test, and found no change in audio sound while changing video qualities. No surprise there as it just confirms what the network traffic shows.


Official Bitrate Table


My findings are counter to what Google has published in this article, which has this bitrate table:

ResolutionMono BitrateStereo Bitrate5.1 BitrateFormat
2160p (4k)128 kbps384 kbps512 kbpsAAC
1440p (2k)128 kbps384 kbps512 kbpsAAC
1080p128 kbps384 kbps512 kbpsAAC
720p128 kbps384 kbps512 kbpsAAC
480p64 kbps128 kbps196 kbpsAAC
360p64 kbps128 kbps196 kbpsAAC

My tests all showed around 126 kbps audio for videos big and small. I did not test 5.1 though, only stereo.


Technical Details of Network Traffic


For more details on how YouTube streams video and audio, and the http requests involved, please see this post.


Legacy Audio Quality


YouTube didn't always have a set audio stream. Prior to 2014, YouTube would play a specific audio bitrate depending on the video quality selected. For example: 240p would get 64 kbps MP3, 360p would get 128 kbps AAC, and 720p would get 192 kbps AAC. For a full list of the legacy bitrates that YouTube used, see these tables.

From July 2012 to some time in 2013, YouTube used these bitrates, as long as the originally-uploaded video had a high-enough bitrate or was lossless.

ResolutionAudio Bit RateCompression
Original192 kbpsAAC
1080p192 kbpsAAC
720p192 kbpsAAC
480p128 kbpsAAC
360p128 kbpsAAC
240p64 kbpsMP3

  • Occasionally you could find a 240p-only video that had a 96 kbps audio bitrate.
  • YouTube would often update older videos to play better audio quality, if that higher quality audio was saved when it was originally uploaded.


Prior to July 2012, YouTube used these audio qualities:

ResolutionAudio Bit RateCompression
Original152 kbpsAAC
1080p152 kbpsAAC
720p152 kbpsAAC
480p128 kbpsAAC
360p128 kbpsAAC
240p64 kbpsMP3


Prior to May 2011, YouTube used these audio qualities:

ResolutionAudio Bit RateCompression
1080p128 kbpsAAC
720p128 kbpsAAC
480p128 kbpsAAC
360p128 kbpsAAC
240p64 kbpsMP3


Prior to March 2011, YouTube used these audio qualities for several years:

ResolutionAudio Bit RateCompression
1080p128 kbpsAAC
720p128 kbpsAAC
480p96 kbpsAAC
360p96 kbpsAAC
240p64 kbpsMP3
Share This Post
Facebook Twitter

Comments


H3XED © Nick Vogt   RSS   Privacy Policy   @Facebook   @Twitter   @Google+