Macenstein

Posted by Dr. Macenstein

What is normalization, and why would you want to do it to your video iPod files?

Well, normalization is the process of increasing (or in some cases, decreasing) the volume of an audio file by increasing the amplitude of the audio waveform to the maximum level possible without introducing any distortion into the recording. (see my illustration below).

Above: You can see the audio from my original EyeTV recording of SpongeBob Squarepants (left) is quite low. After normalization (right) the sound is loud and clear.

Why would you ever want to normalize the audio track of an iPod video? Well, in my case, I happen to bee an avid EyeTV user. I have my EyeTV hooked to my Dish Network receiver, and for whatever reason, the audio level in my recordings is always low. I do not know if this due to the level it comes out of the Dish receiver, or the way EyeTV records it (I suspect the DISH), but whatever the reason, I find the volume to be low. It isn’t so low as to be unlistenable, (for instance, it sounds just fine on the iPod using headphones) but when hooked to external speakers, I must set my iPod’s volume to 100% for a decent volume, where a setting of 50% or lower works for music.

I have also noticed this with DVD rips made directly using HandBrake (although it is not as severe), as well as with rips that I made by first using MacTheRipper, then Popcorn to export. In general, pretty much any video you have encoded yourself for the iPod/Apple TV (or downloaded via a Torrent) could likely use a little (or a lot) of normalization. [Note: you will not be able to normalize protected media such as videos purchased from the iTunes store].

The Problem

The big problem I faced is I wanted a solution that didn’t involve any video recompression, and preferably no audio compression as well. Since my collection of iPod videos is now over 400 titles (most of which are programs recorded off NICK or TOON for the kids), the thought of waiting through lengthy recompression times was frightening. On top of that, I was already starting with pre-compressed files, so I wanted to avoid doubly compressing a file if possible.

The 2-Part Solution: Fission and QT Pro

The answer to my problem came when we received a review copy of Fission from Rogue Amoeba Software. After playing with the program a little, I came to realize it was potentially the answer to my video normalization prayers. One of Fission’s biggest selling features is it can edit audio losslessly, meaning you can copy, paste and trim audio, as well as split files, all with no quality loss. You can also normalize audio, which is what I was really looking to do.

So here is my 2-5 minute solution for normalizing the audio in an existing iPod video, without having to recompress the video track. You’ll need a copy of Fission ($32), and QuickTime Pro ($29.99) to do it.

Step 1. Import your video into Fission. I started out by taking my existing SpongeBob SquarePants .m4v file (which I had previously recorded in Eye TV, edited out the commercials, and exported for the iPod) and opened it in Fission. (Only the audio of the movie will open in Fission).

Step 2. Normalize the Audio. Just select the entire track (Select All) and hit the “Normalize” button.

Above: Normalize the audio.

Step 3. Choose “Save Audio” from the File menu and choose “Save Audio AAC (Original Format Lossless)”. Be sure to give it a new name.

I ran into a little snag in Step 3 because the source of my videos is EyeTV. Apparently EyeTV exports its recordings to iPod with an audio sample rate of 48.000 kHz instead of the traditional 44.1 kHz sample rate used by Apple and apps like Handbrake. When I went to “Save Audio” in Fission, I was not presented with the standard “Save Audio AAC (Original Format Lossless)” option I usually see. Instead, because of the 48.000 kHz sample rate, I was forced to export using Fission’s QuickTime exporter. This is regrettable, as it means the audio is likely being recompressed, but to be honest, you would hard pressed to notice a difference, and the export happens extremely fast (maybe 2 minutes for a 1 hr 40 min movie).

Unfortunately, EyeTV does not let you customize your export to iPod settings, so I am stuck with 48 kHz audio, and an extra 2 minutes added to the process. However, if your source is Handbrake, or a video exported via Apple’s QuickTime app, then you should be fine.

Step 4. Open both your original iPod video and your newly “normalized from Fission” audio track in QuickTime Pro.

Step 5. Extract your video track. With your original video selected in QT Pro, choose WINDOW>Show Movie Properties (Cmnd + J). Highlight your “Sound Track” layer, and hit the DELETE button at the top of the Movie Properties window. You now have a video with no audio. Click back on your QuickTime video window, and SELECT ALL (Cmnd + A), then COPY (Cmnd + C).

Above: Delete your current audio track.

[NOTE FOR Eye TV USERS. If you are using EyeTV, and had to do the audio export thing I mentioned in step 3, when you open your exported audio in QuickTime, you will see 2 extra tracks listed in the Movie Properties box (an MPEG-4 SDSM Track, and an MPEG-4 ODSM Track). I have no idea what these are, and you can leave them if you want, but I prefer to select them and delete them at this point, as they seem to add nothing.

Step 6. Add your video to your new audio. In QuickTime Pro, click on your new, normalized audio, and then choose FILE> Add to Selection & Scale. I learned this step was important, as when you export audio from Fission it can sometimes come out a 100th of second shorter than the original. By choosing to scale the video, QuickTime will force the video to fit the exact length of the audio. I found that otherwise the final new video will not sync to the iPod. This retiming of the video does not seem to add any export time or cause a video recompression under export.

Step 7. Save movie. From QuickTime Pro, now save your new movie by choosing FILE> Save As. Choose “Self-Contained Movie”. QuickTime will quickly marry the two together (approx 30 seconds for a 1:30 hr movie), and give you a brand new movie that should be almost identical is size as your original iPod video, but the audio will now sound much louder and clearer, without any distortion.

Above: The finished new audio track married to the “old” video track. Notice the runtime is now .01 seconds shorter than the original.

The entire process should take you about 2 minutes as opposed to an hour-long (or more) traditional iPod video re-export, and your video should remain at the same quality as your original export. The audio should as well, depending on whether the original iPod video you are attempting to normalize has the correct 44.1 kHz sample rate to begin with. As I said, my EyeTV exports required an extra 1 to 2-minute audio export from Fission due to their 48.000 kHz sample rate.

One thing to note about your newly normalized videos. QuickTime will save the files out with a “.mov” extension, not an “.mp4” or “.m4v” extension you may have started with. You should leave the extension alone. While you can rename the file to a “.m4v” extension, and it will play fine on your computer and in iTunes, it will not copy to the iPod for some reason. So I suggest leaving it alone.

Above: ARRR you ready (for some louder audio) kids?!.

So there you have it, my solution for quick iPod video normalization without recompression. I’m not sure if anyone else on the planet feels the need to do this besides me, but I just thought I’d share.

Now, while it is only a 2-4 minute process, it is still not something I am looking forward to going though with all 400 of my videos. So my plan is to perform the procedure only on new recordings as I make them, and perhaps select older recordings that I anticipate watching more often. I am also looking into creating an Automator action or 2 to speed up the process.