Why wont it accept mp4?

[lilhobo]

How can i hack it to accept mp4?

[yetanotherid]

It was really only designed to convert DVD files.
However, you can trick it into converting the video inside MP4 and MKV files. Rather than type it all again, read my post #5 here:
http://forum.doom9.org/showthread.php?t=158781
I mentioned the need for having the Haali splitter installed in that post. Thinking about it now, you probably don't need it for converting MP4s, but if it fails just install the splitter, or even better the entire CCCP if you're not already using it.

Because AutoGK expects VirtualDubMod to demux the audio from the files and convert the extracted audio streams, it won't convert the audio. You have to deselect it before you start the conversion or it'll fail before it gets to the video. As explained in my post in the other thread, for converting the audio I use foobar2000. I use it as an audio player anyway but it's a really easy to use audio converter once it's set up properly, especially as it'll load, play and convert the audio streams inside MP4 and MKV files so you don't even have to bother extracting them first. Plus by using two different programs you can convert the audio and video at the same time.
Once you've used AutoGK to convert the video and foobar2000 (or whatever) to convert the audio then you just have to open the AVI AutoGK produced with VirtualDubMod, add the audio stream and resave it as a new AVI and you're done. If you're not familiar with the process it's fairly easy but post back if you need help. Just make sure to select "Direct Stream Copy" when you save the video and audio as a completed AVI or VirtualDubMod will set about converting the video again rather than just copy the video you've already converted using AutoGK.

Some more information....
There's alternative methods which involve extracting the audio and video streams from the MP4 and putting them inside an AVI for converting with AutoGK, which means AutoGK can then extract and convert the audio itself. However it takes longer and you're still limited to the few types of audio AutoGK supports. MPEG, and AC3 etc. YAMB will extract the video stream from MP4s and put them inside an AVI, and MKVCleaver will do the same for MKVs. I don't think either will put the audio inside the AVI though. Once you've created an AVI using the video from your MP4 or MKV you still have to open it with VirtualDubMod, add the audio stream and resave the AVI for AutoGK to convert yourself, which means the process of converting them I mentioned in the other thread is generally easier.

One more tip. Sometimes audio inside MP4s and MKVs is delayed, just as it can be inside vob files (have you noticed when AutoGK extracts and converts the audio it saves the delay value as part of the audio file name?) So if the audio is delayed you've generally got to work out the delay yourself. I usually open the newly created AVI using Media Player Classic Home Cinema and alter the delay until it's right by tapping the plus and minus keys. Once I'm happy with it I use the delay value displayed on MPC-HC's status bar to resave the AVI using the same audio delay.
When converting MKVs it's possible to work out the delay used exactly (assuming it's correct, depending on where the MKV came from). You can open an MKV with MKVCleaver and select the audio and timecodes boxes (select timecodes only from the top menu) and then extract. MKVCleaver will save a text file containing the audio timecodes to your drive. The first number in the text file is the audio delay. I don't know how to work out the delay for MP4s as I rarely use them. The first thing I generally do with an MP4 is to remux it as an MKV with MKVToolNix so I can delete it. It's not that I've got anything against MP4s as such, it's just that MKVs are far more versatile, and as I waste too much time on this sort of thing I prefer to work with them. Re-muxing MKVs and adding and extracting streams etc is much, much, much, faster using MKVToolNix and MKVCleaver than it is when trying to do the same thing with YAMB and MP4s. Much faster. And MKVToolNix doesn't do my head in trying to work out why the change I made didn't have the expected effect when I've resaved the file like YAMB often does.

[yetanotherid]

I thought of yet one more method, and this one should let you open any file you can play on your PC and convert it with AutoGK if all else fails, but once again it still involves encoding the audio separately.

As you have AutoGK installed you'll also have AVISynth installed. You can create a basic script to open any video file yourself, or if you're lazy like me look for a program called AVISynthesizer via Google. It adds an Explorer right click option which lets you create a simple AVISynth script pointing to any file with just a mouse click or two. You can then open the script with Media Player Classic Home Cinema and it'll play just like it was playing the original file, only it's doing so via AVISynth.
Once you have your AVISynth script you've then got to get AutoGK to open it, which it won't because it doesn't open scripts. So using a little utility called MakeAVIS, which comes with the full version of ffdshow, or with another called avs2avi, you then wrap your AVISynth script into a new AVI. Now you have a new AVI which is probably only a few kilobytes in size and which AutoGK will open. It should convert the video as usual regardless of the original file's format or the type of video inside.... as long as you already have the right codec to play the original file on your PC.

Audio still needs to be converted separately so it's foobar2000 to the rescue again. If you have the foobar2000 AVS and DirectShow input plugins installed then once again if you can play the audio on your PC, foobar2000 can to.... and convert it of course. Don't forget if you have ffdshow installed foobar2000 is converting the ffdshow decoder's output, so anything the decoder is doing to alter the audio will be included in the conversion. For instance if you normally have the decoder set to mix down to stereo, then you'll need to disable the mixer while you convert 5.1ch audio if you want to keep 5.1ch audio.
I have found for some reason there's a bit of a volume drop when converting via DirectShow using foobar2000, so for that reason I've got into the habit of boosting it a bit before converting, either via the ffdshow decoder or using the ReplayGain function (you can tell it to alter the volume by a specific amount when no ReplayGain information is found). A 6db boost usually does the job. That might only apply when converting 5.1ch audio and mixing it to stereo. I haven't done a straight stereo to stereo conversion via DirectShow for quite a while so I can't remember if the same thing happens.

That's 3 different ways to convert video to AVI using AutoGK now, so if the simple (change the file extension) method doesn't work the third method should. Hopefully I haven't made it sound overly complicated. Setting up foobar2000 with the correct plugins and decoders is probably the hardest part if you've not used it before, but once you've got it working properly and converted a few times the whole process becomes fairly easy. Foobar2000 will also save conversion settings as presets (for instance I've got presets for converting to MP3, AAC and AC3 etc, some to mix 5.1ch to stereo, some to keep 5.1ch audio, so converting the audio is just a matter of opening it with foobar2000, right clicking on it's entry in the playlist and selecting the appropriate preset.