Questions about the x264 codec

[kaz219]

I'm actually playing around with the x264 codec. The quality/size ratio is amazing... and I have some questions, of course:

First, how to add an audio track to a mp4 file? If I use the "mux" tool, it try to create an avi file, isn't it? And when I look at the time it takes (I didn't wait until the end and stopped it), I'm really curious to know what it is really doing during this muxing.

Second, it would be great to be able to choose the container and the audio codec. Or is there a reason why there is no choice? I know for example that D-Vision is putting x264 encoded videos in an avi container, with any audio format. Does mp4 only support AAC? Why then mp4?

Third, talking about containers, what are the advantages of mp4 over avi? I've heard some things about the "obsolete" avi format, so I'm curious. Is it possible for example to put selectable subtitles in the mp4 file? (NOT burned subtitles)

[major]

The mux tool does not support h264 for now. mp4 is the standard container for h264 (avi is not standard and it should be never used for h264) and it supports any codec and subtitles.

[kaz219]

Thanx for the answers!

If you know of any software that can add/remove audio tracks in mp4 files, I'm really interested. Same for adding/removing subtitles in a mp4 file...

[kaz219]

Actually, why shouldn't avi be used for H.264? I mean, what are the consequences?

[major]

The consequences are lack of support and further spread of a primitive video container.

[kaz219]

ok, I gave a try to MP4Box (thanx anaxamander).

Works great for adding audio tracks, except that Quicktime is not able anymore to open the file afterwards.
For adding subtitles, it seems to works, but I couldn't find a software able to read embedded subtitles in a mp4 file. (vlc or mplayer can't)

So, it seems that mp4 is "too modern", since most softwares are not able to make use of its possibilities. But it will come, I suppose.

[kaz219]

For H.264, I found out an inconvenient (which can seem obvious for some people out here): it is *very* CPU intensive. I have a 720x576 pixels movie, and my 1.3GHz G4 is at its maximum to play it. Even a 720x304 movie is using the full power of my CPU in very dynamic scenes... Crazy.

Thus, it's interesting to considere the following trade-off, on portable devices:
Is it better to use Xvid movies, consuming more memory, or
is it better to use H264 movies, consuming more CPU ressources and thus more battteries?

If somebody has some benchmarks about this metrics, I'm curious...

[major]

Indeed it is pretty normal that it is CPU intensive, since it requires an insane amount of computation, which translates into quality and compression.