Audio Commentary
From SDA Knowledge Base
Contents
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. It's about time, isn't it? The main reason it took so long is because QuickTime 7 doesn't handle multiple audio tracks properly, and it still doesn't but we've found a semi-solution. As it is now, QuickTime 7 will play all audio tracks at the same time, not very pleasant to the ears. The idea is simple: disable the secondary audio track so that QuickTime won't play it, while all other decent media players will still have the option.
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. MP3 will not work. 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. Notice the audio section lets you pick only two audio streams at a time. To add more, first save the file with the two streams. Load that into the Video Input field, it will recognize that there's already audio tracks inside. Then just repeat like before. 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. Be sure to double-check your work in QuickTime when you're done.
You have two options:
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
- 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.
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