You guys have always sorted out my problems in the past so here goes:-
I am comping a photo slideshow with a bit of video and text for an audio journalist to upload to a web site. I have previously used Flix Standard for web encoding which uses ON2's VP6 codec, it is the most backward compatible with Flash Plugins (H.264 requires Flash plugin 9 I believe). The text and transitions don't look too great and the web guy suggested H.264. In Flix I import an uncompressed avi 50i PAL and make sure it is de-interlaced and export using that. I can however export directly from AFX by selecting the H.264 codec, shrink to size in the Output module (I'm using 512x288) and render. I end up with a .Mp4 file which looks pretty good but I am not sure how to ensure that the playback bit rate is within the limits for the web. I can select CBR; the two other controls are profile which is pre set to Main and Level which is preset to 3. A 30 second clip encodes to about 7Mb and plays back great in Quicktime afterwards, but how do I check or indeed alter the maximum bitrate settings? What workflow would you suggest for comping what is mainly a series of photographs with transitions and some scale movement plus titles, and how can I encode it to H.264 ready for the web guy. Do I need some stand alone encoder, I have heard that the out of the box encoders that ship with AFX and Premiere will never be as good as specialised software which is why I bought Flix. It does seem that the settings for the H.264 codec in AFX are pretty basic with not much control over bit rate settings and all the other stuff (which I don't confess to understand in full but I could certainly bone up a bit if necessary). I'm not even sure what bit rate is best for streaming from the web anyway I assume about 400kbps? The output file is .mp4 will that stream directly through the Flash Plugin? Aaargh so many questions so little time, please help.
If you want to encode video with H.264 for playback in Flash Player on the Web, consider rendering and exporting to an F4V container.
There's a lot of information about H.264 and F4V files in the "Render and export a composition as an FLV or F4V file" section of After Effects Help. That page also links to several resources that go into much more detail about compression options for H.264.
Alternatively, if you are going to use a separate, third-party encoder to create your H.264 files, then don't encode to H.264 from After Effects; rather, create a losslessly compressed master movie that you then run through your encoder.