Muxing Nightmare

[InPin]

I've been trying to mux together a mp2 audio and mpeg2 video track encoded from a QT mov (which was itself exported from iMovie) for eventual burning as a SVCD. Previewing the mpeg2 video layer in VLC shows that it's in fine shape; likewise, the mp2 audio layer sounds just like it should. However, the muxed mpeg is absolutely horrible -- the video is jerky, and the audio varies wildly in speed. I've tried both MissingMPEGTools and ffmpegX to encode the audio and video layers and mux them together, but both gave the same result (presumably because both use mplex to do the multiplexing?). I'm working on a 1GHz iMac, 768 MB RAM, so I should have the horsepower for VLC to preview the muxed video, I would think. I've been tearing my hair out trying to figure this out. Might anyone have any pointers on how I can get this to work? Thanks.

[galactica]

are the two of the same length in time?

ie. movie is 69 min audio is 69 min? If not, you will get what you are talking about.

also, what were you encoding from? Its generally a good idea to have ffmpegx do both encoding and muxing at the same time, rather than encoding first, then muxing later.

[InPin]

I assume they are -- I encoded the audio and video using both MMT and ffMpegX (having ffmpegx simulataneously mux them as well), with identical results. I've tried to verify the track lengths using VLC and it's not displaying any times at all. Is there any other way I can check to see how long they are? If they are not the same length, can I append an offset of some tip to make up the difference?

Thanks.

[galactica]

http://www.versiontracker.com/dyn/moreinfo/macosx/12845

mpeg info. will give you "INFO" on your mpeg and your mp2 files.

post results here.

[Mr.Radar]

the video is jerky, and the audio varies wildly in speed

While I'm a windows user I've had this problem in the past and it turned out to be a bad MP2 file. Try using a different audio encoder(or try linear PCM audio).

[InPin]

You're right -- they are of different lengths. Here's the info:

Audio : Mpeg 1 layer 2
Estimated Duration: 03:53.87s
224 kbps 44100 Hz
Frame size: 731 bytes
Stereo, No emphasis, copy

Mpeg 2 Video File
Estimated Duration: 03:00.54s
Aspect ratio 4/3 (TV)
Interlaced, chroma format: 4:2:0
Video Format: NTSC
Size [480 x 480] 29.97 fps 2.50 Mbps

This is my first SVCD project, so I'm a little confused. If the audio and video were encoded from the same QT file, how did they wind up being different lengths? Is there any way I can fix it? I'm trying ffmpegx as I type this, only this time I'm going to keep the elementary streams and see what they show. I imagine it will be the same story.

Thank you again. I'm learning alot.

[galactica]

actually, its quite common. I would always get this when i started learning SVCD conversions.

To be honest, its all got to do with where its coming from. you say QT file. Where did that come from? Did you convert it to QT? Was it a divx? etc.

For the best svcd (ie easiest to keep muxed properly) dvd to svcd would be the way to go.

If you have a source such as .avi or .mov or somethign thats already been encoded to something else, its more difficult (though doable)

It really depends on where the QT file came from. Quicktime can have "anchored" video. If you think about it take a rope 6 feet long (audio) and another of 6 feet 6inches (video). lay them down against each other and audio is longer! but, tape them in various portions where there's a little buckle of the video and it fits! this can be how the audio or video are differnet lengths.

for audio its noticable (pitch changes usually towards higher frequencies) result of pinning down a longer audio file.

For video its not so noticable (there, but your eyes cant really tell) that the video is streched or compressed.

SO, to make a long story short, where and how did you get the qt file?

[InPin]

Thanks again for the help. This is really enlightening. I exported the movie as Full Quality DV from iMovie, which resulted in its being saved as a QT .mov.

[havema-1]

http://www.versiontracker.com/dyn/moreinfo/macosx/12845

mpeg info. will give you "INFO" on your mpeg and your mp2 files.

Notice that MPEG Info X 0.2 still has a bug in "Estimated Duration" for MPEG2 files because it AFAIK has an old version of mpgtx. BTW the same bug affects also VCD Builder 1.1.1 and one needs to replace the mpgtx engine with a newer one to be able to insert chapter points to right places in VCD Builder.

mpgtx GUI has an updated version of mpgtx and it shows MPEG durations correctly:

<http://www.biermann.org/philipp/mpegcut/>

[ZeroSix]

there is another solution, but it involves creating an XSVCD.

Open your movie in quicktime and export it using the MPEG2 export. From the export dialog you can tell it whether or not to save the audio and in the case the answer is YES!

You will end up with a .m2v file and a .aif file. Since the .aif file is very large, it is necessary to convert this to a .AC3 or .MP2 file for the audio. I highly recommend AC3 for SVCD, but i have had some troubles on a few set top DVD players, so you might want to consider .MP2.

Regardless, open the .aif file in quicktime and export that to WAVE.

Open ffmpegX and convert the audio to a .ac3 file.

If you want to use .mp2, launch the terminal and type the following:

mp2enc -V -o /path/to/output.mp2 < /path/to/input.wav

Once you have your resulting .mp2 or .ac3 file, launch ffmpegx, go to the TOOLS tab open your audio file and your video file, tell it to mux as xsvcd and post-process, making a svcd images.

The entire purpose of using the apple quicktime 2 export is because it will automatically adjust the audio and the video so that they remain in sync and retain the exact same duration. The same holds true for the Toast VCD export. For example, you could take a source movie that has a framerate of 10fps, export it in quicktime and the resulting mpeg will in fact be 29.97 fps with ZERO loss in sync.

Just make sure that you use a standard SVCD bitrate for the video and then use a standard bitrate for the audio if using AC3. If you use the terminal command above, it will automatically make a SVCD/VCD compliant audio stream from your wave file.

This may sound like a lot of steps, but it is a very quick process, especially if you have a newer mac and it is a fool proof way that I have found to eliminate the problems that you are describing.

I'll try my best to help you get this going if you have any ?'s.

[InPin]

Thanks for the suggestion and your offer to help. I have a killer day at work tomorrow and I need to prep for it tonight, but I'll definitely give this a try tomorrow evening and let you know how it goes.

Thanks again.

[InPin]

ZeroSix:

I loaded my movie in Quicktime, but I don't see any options for exporting. I suppose I would need QT Pro for that kind of fuctionality?

[galactica]

well yea, qt pro AND you would need to have DVD STUDIO PRO installed, which gives you mpeg2 export.

[InPin]

Guess I'm stuck, then. I don't have either.

[InPin]

Is this really the only way (meaning QT Pro and DVD Studio Pro?)? Might it be possible to use one of the other export modes in iMovie?

[galactica]

uhhhh not that I am aware of. Perhaps there is and im just not thinking of it at the moment!