Audio on youtube

[themoog]

Guys I know there are many posts on the quality of audio on youtube, here is my problem

http://www.youtube.com/watch?v=Xpd0FuJbjDs

I wanted to guarantee a good -18dbFS audio resource on the web (check out my blog post http://www.themoog.org/archives/338).

Anyway I upload a clean sine wave to youtube and when it plays back via the browser there is some serious aliasing going on.

My upload settings are the following

For video

Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L3.2
Format settings, CABAC : No
Format settings, ReFrames : 2 frames
Format settings, GOP : M=1, N=24
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 30s 0ms
Bit rate : 316 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Progressive

For audio

Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 30s 0ms
Bit rate mode : Constant
Bit rate : 181 Kbps
Nominal bit rate : 256 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 44.1 KHz
Compression mode : Lossy

Ive tried playing back in HQ mode..... Same......To be honest I get the same with vimeo.

Any ideas on how I can cheat the youtube transcode?

Many thanks

Neil

[poisondeathray]

Any ideas on how I can cheat the youtube transcode?

If you mean "cheat" them so it doesn't re-encode both video & audio, it's currently not possible for YT


There is a "cheat" for blip.tv, if you upload wrapped in flv, it will allow passthrough, but flash only supports 44.1Khz audio streams

[intracube]

Anyway I upload a clean sine wave to youtube and when it plays back via the browser there is some serious aliasing going on.

How are you measuring this aliasing?

I've just done a comparison of a file uploaded to YouTube, and the same file downloaded with DownloadHelper - which eliminates any issues with Adobe Flash.

Comparing the sine waves in Audacity, the YouTube converted sound has some instability in the amplitude (I can post some screenshots tomorrow if you're interested). As Flash plays no part in this, it must be YouTube's conversion process that's causing the drop in quality.

I guess I'd describe the sound distortion as 'fluttering'. But the common usage of flutter is a variation in frequency - and I'm not sure that this is.

This isn't the same issue that you're seeing, but it's worth downloading a file from YT and playing in various media players as a process of elimination.

[themoog]

Thanks intacube for your time out on this one.

To be fair aliasing might not be quite the right term and yes there is a "flutter" type feel, but as you say flutter and aliasing are both frequency domain artefacts... I'm using my fav tool http://www.audiofile-engineering.com/spectre/ to measure the signal, and yes I'm seeing amplitude variations.

Other than aliasing though I can't think what compression type atrifact might cause this effect...? Next time I'm at my computer I'll run it (the you tube converted siine wave) through spectre again and look at it with the spectrum analyser to see if frequency variations are still the root cause..

Good tip on download helper btw...

Thank in advance

Neil

[intracube]

This is what I'm seeing from audacity:


I'm half wondering if YouTube is adding some sort of watermarking to the audio. I can't see any reason why 128kbps AAC audio should have such noticeable artefacts.

I double checked the original file I uploaded to YT (128kbps mp3 audio) and that looks fine.

[themoog]

So intracube as i thought, looking at the spectrograph there seems to be lots of harmonic content

http://youtu.be/uiDHHTsDRCQ

Might help demonstrate (you need to watch in fullscreen, and yes theres a screen flow watermark, I'm still deciding whether to buy it of not)

Next step is to try encoding sine waves at different rates, bit depths ect.... to see if I can replicate this.

Neil