Audio Commentary

Introduction

SDA allows audio commentary in the form of a secondary audio track in an existing H.264/AAC audio/video stream. In other words, one video stream and two audio streams in one MP4 container. However, you must disable the secondary audio track so that QuickTime won't play it at the same time as the first (but still letting people switch to it if they want). This is easy to do and instructions are given later on this page. You don't actually even need QuickTime to do it.

Multiple audio tracks in the AVI container is still not allowed. Windows Media Player also happens to play all audio tracks at the same time.

Record yourself

Editor's note: This is just some basic information. If you have more to add, please flesh this section out. I'm no sound expert.

First get a microphone if you don't have one. You'll need a recording program. Audacity is a good choice. You will probably want to play around with it first to know how loud to talk, where to put the microphone, how to edit afterwards, etc. If there is static in your test recording, try using the Noise Removal tool. Select a sample of just noise, then go to Effects, Noise Removal and select "Get Noise Profile." Now select the entire recording, go to Noise Removal again, and click "Remove Noise." If the slider was too far left, there will still be a lot of noise; if it was too far right, your voice will get distorted and sound like a robot. Try adjusting the slider until you find a good balance. If you talk louder, you will probably have an easier time removing static. You can also try using Noise Removal multiple times. The best thing to do is to play around until you find what works. After you have gotten rid of noise, if you want to remove other sounds, highlight them and click Generate, Silence. If you just delete, you will get out of sync. After you are done, you will want to amplify the sound. Select the entire recording and go to Effects, Amplify. The setting provided will probably be good, so click Okay. If you listen to it and it sounds distorted, undo and try a smaller amplification.

When you actually do your commentary, you'll want to do everything the same as you did for your test recording. Press record, then play your video. Make sure the sound is off (it's best to set it to mute within the media player itself) or you may end up automatically recording the game sound. The game sound and the commentary can still be mixed together later, but it's best to get just the commentary and then combine the two. If you do not want to do the commentary all at once, you can do it in parts and combine them. When you are done, stop it and do noise removal, amplification, etc. If you want to have your commentary be without the game sound, export as wav. If you want the game sound mixed in, go to Project, Import Audio and select your game audio. Adjust the volume of each using the sliders at the left. When you have found a good volume for each, export as wav. It's a good idea to save the project file as well.

Mixing / Compressing / Muxing the audio

Once you've recorded your commentary, you may want to consider mixing it with the gameplay audio, but at a low volume so that we can still hear you. Audacity, a free sound editor is capable of doing this.

Load your finished wav file in MeGUI for compression to AAC. DO NOT USE MP3! It is incompatible with QuickTime 7 and people will wonder why they can't open your run.

SDA is fairly strict about choosing the bitrate corresponding to whichever quality version you're encoding. However, with audio commentary it's quite lax; do whatever sounds good. Commentary with just the voice and no gameplay audio mixed in can go as low as 32 kbps and still sound good. If you're adding commentary to the LQ version, use mono 32 kbps.

Use MeGUI again to add the audio commentary. To add more streams, right click the "Audio 1" tab and select "add track". Don't get carried away, though, more audio tracks equals a bigger filesize. Consider lowering the bitrate of the commentary tracks if you have to. To make it easier for you later on, be consistent with which stream becomes input #1 and which stream becomes input #2. I suggest putting the gameplay audio as input #1.

Tip: YAMB can also mux files for you and has other useful features.

Disabling the audio commentary for QuickTime 7

You absolutely must do this, even if it may be tedious to do so.

You have three options:

• With DJGrenola's mp4nerf.exe.
• With Apple's dumpster.exe. (tedious)
• Mux with Mp4Box instead

mp4nerf

This program will look for all audio/video tracks and disable any that it finds after the second. So make sure the gameplay audio/video are tracks one and two, audio commentary as track three or higher.

• Download mp4nerf.
• Run mp4nerf through the command line or use the batch file by dragging MP4 files on top of nerfit.bat.
• The batch file will ask for confirmation, saying no will only display the matches that mp4nerf has found.
• All done!

dumpster

Note that this method does not work if you are running an x64 edition of Windows.

• First, you'll need to download and extract Dumpster (mirror).
• Drag the MP4 file over dumpster.exe to load the program.
• Double-click the line with 'moov'.
• You'll see three 'trak' items. The first is probably the video track, the third is probably your second audio track. Double-click on that third 'trak' item.
• Double-click 'tkhd'.
• Select the line with 'flags'

• Change $000001 into $000000
• Click Apply.
• All done!

Warning: If you do any re-muxing of a file, it may reset the flag to $000001 and you'll have to start over.

mp4box

MP4Box is the command line program behind MeGUI and YAMB responsible for muxing streams into an MP4 container. You'll need to call it directly from the command line to disable the commentary track, since MeGUI and YAMB do not expose this functionality.

Put your video in the same directory as MP4Box.exe, open a command prompt in that folder and run the following command:

mp4box -new -add source_video.mp4:name=Video -add "source_audio.mp4:name=Game Sounds" -add commentary.mp4:name=Commentary:disable final_video.mp4

Or, if you already have your MP4 file with audio on it and just want to add your commentary track to it:

mp4box -new -add source_video.mp4#video:name=Video -add "source_video.mp4#audio:name=Game Sounds" -add commentary.mp4:name=Commentary:disable final_video.mp4

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