Bug: Ignores AAC bitrate setting when converting VOB to MP4

[macr0t0r]

This has been mentioned briefly in the past, but the subject never really described the bug. So here it is:

I like to use MTR to rip my DVD to a title VOB, then encode using FFMPEGX. However, now that I am trying to fit these on an iPod, I have noticed a glitch:

The resulting MP4 file always seems to have the AAC sound encoded at around 190kbps. I can change the frequency, which then causes it to drop to around 183kbps, but I can't alter the bitrate. CBR, VBR, invert mapping, etc. The bitrate setting is ALWAYS ignored. Since the iPod can't handle anything over 160kbps, I'm at a bit of a loss.

This error doesn't show up with any other video source format. Currently, my solution is to go ahead and encode, then re-encode the audio in Quicktime Pro (since FFMPEGX does not support video pass-thru for MP4 files...but that's another post).

I'm using an iMac G4 (1GHZ) with FFMPEGX 0.0.9t. This glitch existed in the last two versions as well.

It should be noted that Handbrake does not have this glitch. However, I like the customization controls in FFMPEGX, so I'm hoping to make this work.

[macr0t0r]

Let's throw some more detail in, shall we?
I'm converting a quick BlueManGroup video to XVID MP4 wtih 128kbps AAC sound. Here is the log output:
=====================================
Encoding started on Thu Dec 8 08:39:35 PST 2005
Input #0, mpeg, from '/Users/jim/Movies/THECOMPLEXLIVEDVD Title 2 (Ch1 - Ch1)/VIDEO_TS/THECOMPLEXLIVEDVD Title 2 (Ch1 - Ch1).VOB':
Duration: 00:03:36.1, start: 0.280633, bitrate: 5307 kb/s
Stream #0.0: Video: mpeg2video, 720x480, 29.97 fps
Stream #0.1: Audio: ac3, 48000 Hz, stereo, 224 kb/s
Output #0, mp4, to '/Users/jim/Movies/singalong.mp4':
Stream #0.0: Video: xvid, 640x352, 29.97 fps, q=2-9, 2300 kb/s
Stream #0.1: Audio: aac, 48000 Hz, stereo, 128 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Stream #0.1 -> #0.1
video:38355kB audio:5022kB global headers:0kB muxing overhead 0.302942%
bench: utime=1018.440s
1 video MPEG-4 Unknown Profile(0), 216.249 secs, 98 kbps, 640x352 @ 29.97 fps
2 audio MPEG-4 AAC LC, 216.064 secs, 98 kbps, 48000 Hz
Warning:Sampling rate must 24KHz.
Encoding completed on Thu Dec 8 09:01:45 PST 2005
=====================================

Strange, no? It clearly states it intends to encode at 128, but the it claims the resulting streams are both at 98kbps (including video). Fine, let's load the resulting file into FFMPEGX and see what it says. Hmmmm....it lists no bitrates for either video or audio in the summary window. Let's try Quicktime Pro. Ah, now it shows 1450kbps for video and 190kbps for audio. The video plays fine, but the iPod won't accept it since the audio bitrate exceeds its capabilities.

Let's take a look at the terminal command:
/Applications/Video Utilities/ffmpegX_0.0.9ur2/ffmpegX.app//Contents/Resources/ffmpeg2 -i /Users/jim/Movies/VIDEO_TS/SINGALONG.VOB -y -threads 2 -map 0.0:0.0 -f mp4 -vcodec xvid -b 2300 -croptop 62 -cropbottom 62 -cropleft 6 -cropright 4 -s 640x352 -r ntsc -g 150 -me epzs -qmin 2 -qmax 9 -deinterlace -acodec aac -ab 128 -ar 48000 -ac 2 -map 0.1:0.1 -benchmark /Users/jim/Movies/singalong.mp4

Well, it shows the "aac ab -128" quite clearly, so the command is right.

I've tried this on both a G4 and G3 running OS X 10.4.2 with 640MB of RAM. I'm now using ffmpegx v0.0.9ur2.

What's driving me nuts is that this only happens with VOB files. Other files encode correctly to the proper bitrate. Unfortunately, this is the primary use I intend for FFMPEGX. Handbrake has proven to be limited and buggy.

Anyhow, I can continue to re-encode the audio in Quicktime Pro, but I know there will be a slight quality-loss because of that.

Any ideas? Any thing else I can do to provide additional information. major, I can send you a private link to the VOB (136MB) if you wish to test it. I have this issue with many other DVDs, but that is the smallest VOB that has the glitch. I doubt it would be kosher to post it in the forums.

[major]

OK, I'll look into this today.

[macr0t0r]

Thank you very much for looking into it, major! Good luck with it.

[macr0t0r]

Alright, my tinkering conitunes with this infuriating bug. It boils down to conversion of AC3 audio to AAC. It turns out that VLC has the same glitch.

The AC3 audio is stereo (2 channels) at 48khz. When I convert it to AAC at any bitrate, then Quicktime detects it as a 5(!) channel AAC file at about 190kbps. Not sure what is in the other 3 channels. Anyhow, it looks like it is a glitch in the flaac code. This isn't related to the ffmpegx gui. I'm going to see if there is an option to force 2 channel in the command-line.

[macr0t0r]

Am I the only one who has this problem? Sheesh. Anyhow, for those that DO have this problem I found the solution. It appears that major already fixed it, it's just not "turned on" yet in the current release. You know the deal: a fixed bug often generates 3 more bugs.

Anyhow, to re-cap, when I convert a *.vob file to *.mp4 using the iPod TV preset, I noticed that the audio bitrate is ignored. The resulting audio bitrate is usally around 170kbps to 190kbps. Since the iPod is capped at 160kbps, this makes an incompatible file. It also creates a 5-channel sound instead of a 2-channel media.

If you dig into the "contents" of FFMPEGX, you'll see two version of ffmpeg:
ffmpeg: this is the new CVS version.
ffmpeg2: this is from January 2005. A stable, static compile.

When you encode to XVID MP4, it uses ffmpeg2. That version has the AAC glitch. However, if you start to encode, open a terminal, and type:
ps -axwwo command | grep ffmpeg | grep -v grep

You'll get the entire ffmpeg2 command that FFMPEGX generates. Copy and paste the last chunk. Now, stop the process, and then paste the command in the terminal to use ffmpeg instead of ffmpeg2. It should look something like this:
/Applications/ffmpegX.app/Contents/Resources/ffmpeg -i SOURCE.VOB -y -threads 2 -map 0.0:0.0 -f mp4 -vcodec xvid -b 2000 -croptop 58 -cropbottom 54 -cropleft 24 -cropright 24 -s 640x288 -r ntsc -g 240 -me epzs -qmin 3 -qmax 15 -deinterlace -acodec aac -ab 128 -ar 48000 -ac 2 -map 0.2:0.1 -benchmark OUTPUT.MP4

This provides me with everything I want. If you want to take a risk, you could try replacing ffmpeg2 with the newer ffmpeg, but I'm guessing that the newer ffmpeg has some glitches that major was working around by employing two versions of the same program. You may break some other functionality. For me, I just use the terminal approach when converting a DVD.

Hey, major! Any chance of having FFMPEGX utilize the newer ffmpeg when the source is a VOB? Sounds like a potentially easy fix.

EDIT: Okay, here's the bugs of the new ffmpeg:
1) No "preview" ability. That's a biggie for me.
2) Resulting file seems to have some sort of aspect-ratio glitch. Quicktime shows it just fine, vut VLC pillars (stretches vertically) the video somewhat. Running the video through MP4box to clear all extra tags solves the problem. I use MP4Box to attach the subtitles anyway, so this is no biggie.

Anyhow, as I said, I found my solution.

[PaulCali]

I have been searching for answers to my problem with tranferring video to my iPod and stumbled across your post. The videos I would want to transfer were essentially created using the method you use with one exception. I do the following:

MTR -> VOB file -> .avi file (using Xvid mencoder). I do this to create a high quality file that I can watch on my TV's using an eyehome.

I then take the converted .avi files and use ffmpeg to encode them to .mp4s suitable for iPod.

Your post enlightened me that the iPod cannot accept audio bit-rates over 128kbs. That explained why some of my videos would not trandfer at all to the iPod. I used your suggestion to alter my script for converting the videos (used ffmpeg instead of ffmpeg2). Works like a champ!

I have one observation and 1 remaining problem.

Observation: An update must have been released that limited the iPod. I have 20+ movies on my iPod that have audio bit rates over 128kbs. After that update is when my transfers started being spotty.

The remaining problem is that on most any movie I have on the iPod, I start playing it, looks/sounds great. Then it freezes for a few seconds. The video starts rolling again, but there is no audio. If I advance or reqind the video a bit (even by a second), the audio will start playing again.

Sometimes I have to this a couple of times and then the movie will play fine thereafter. Sometimes, it just keeps doing it over and over.

Since you are working with a similar process, I was wondering if you had seen this as well?

And thanks a bunch for posting your solution! I am much closer to where I need to be.

[macr0t0r]

Ah me....you will see this "firmware bug" mentioned in multiple posts in the General section. I guess you have the 60GB version of the Video iPod? For some reason, the latest firmware wrecks havoc on it. I don't have the link, but I hear there is a hack to revert it to the old firmware.

Technically, the ipod can handle 160kbps audio, but AAC encoding always seems to vary a bit, so I limit my encodings to 128 to give me some margin. However, I hear the latest firmware has a bug that forces you to encode at 96kbps if you want a reliable transfer. Unacceptable in my opinion. Either revert your firmware, or hope for an "updated update" real soon.

- macr0t0r

[macr0t0r]

Latest update:

Not sure on how kosher this is...but, if you replace "ffmpeg2" executable in ffmpegx with the "ffmpeg" executable in the latest iSquint 1.2, then you pretty much have full functionality with no more AAC bug.

That pretty much ends this whole charade of debugging. Just needed a more updated compile of ffmpeg. I guess if iSquint uses some of ffmpegx's tools, then it's not too wrong to have ffmpegx use some of iSquint's resources, right? Right? Errrr....whatever it takes. I'm finally happy!

[macr0t0r]

Jeez, the AAC bug is still in version 0.0.9v? Why are you running such an old version of ffmpeg for vobs? Guess I'll replace the ffmpeg2 executable again.

[ArtemisG3]

So maybe this explains why iTunes won't let me copy my ffmpeg-encoded mp4's. I have the bitrate set to 128kbps. Since iTunes won't let me transfer the movies, I've been using this approach. I'll give the newer build of ffmpeg a try.

[rumplestiltskin]

So maybe this explains why iTunes won't let me copy my ffmpeg-encoded mp4's. I have the bitrate set to 128kbps. Since iTunes won't let me transfer the movies, I've been using this approach. I'll give the newer build of ffmpeg a try.

I'm using 9w and usually use 128kb for the audio (48K, of course). Occasionally I use 160kb if there's audio worth the extra bandwidth. I have no trouble dropping these files into my iPod. What are the settings you are using?

[macr0t0r]

It appears version "w" has finally fixed this issue. Cool!

[ArtemisG3]

I was using build 5026 and having problems, but now that I'm using build 5250, all seems to be working.

edit: Just to clarify, I am using ffmpeg (command-line), not ffmpegX.