Hi, John. After my experience with After Effects (I am referencing CS4 and CS5.5 here) and creating video files for the web, I can offer the following:
1) Yes, MP4 is the same as MPEG-4.
2) The “yield” sign is just an FYI to let you know that something will be techinically, and perhaps, perceptually different in the final output file from the orginal (like PAR).
When my final file output is destined for the web, I make the dimensions of my After Effects comp safe for the web/computer screen display. You can do this simply with your encoding preset (like After Effects was telling you it was going to do), but I don’t know that you will want to let it do that for the following reason:
It looks to me that your source WMV is a wide screen video since your dimensions have a ratio of 1.77:1, or 16:9. If this is true, then allowing After Effects to “help” you by resizing it for you will ruin the aspect ratio by changing it to 1.47:1.
To avoid this, disregard what After Effects tells you about your WMV having a PAR of 1.22 (this is the PAR for widescreen NTSC Standard Definition, and I think the WMV format may be showing you the adjusted frame size dimensions instead of the actual pixel dimensions of your clip).
In AE, right-click your footage and select “Interpret Footage>Main”. In the “Main Options” tab and under the “Other Options” heading, change the “pixel aspect ratio” to “Square Pixels”. Now your footage will display in AE as it should appear on the web.
Drag your footage to the “new composition” icon at the bottom of your project panel, and your new comp will be set to 576×324 with square pixels (if it isn’t, change your comp’s frame size to 576×324 with square pixels and scale your footage to fill the frame). The “yield” icon will not appear when you output this video to a video file with the same dimensions.
As far as creating an MP4 (H.264) file, try modifying your “Output Module” settings to:
Video: “Profile: Baseline”; “Level:3.0”; “VBR, 1 Pass”; “Target Bitrate: 1 Mbps”; “Maximum Bitrate: 1.5 Mbps”.
Audio: “Codec: AAC”; “Audio Quality: High”; “Bitrate Settings: 96 kbps”; “Precedence: Bitrate”.
Multiplexer: “MP4”; “Stream Compatibility: Standard” (though you can set this to “iPod”, I have used “Standard” to produce files for iPad).
P.S. It is generally a good idead to output your final video files, whether to the web or desktop use, as close to the video clip’s original frame dimensions and pixel aspect ratio (or intended display dimensions) as possible to preserve the quality of the original as much as possible.
P.P.S. To get a look at what’s under the hood with various video files you may work with, I recommend downloading “MediaInfo” from https://www.download.com.
-Michael
*****
Avid Media Composer 6 (HP Z400 Workstation: Windows 7 64-bit; Intel Xeon 6 Core W3680 CPU; 6 GB RAM); Adobe CS5.5 Production Premium; DepthQ Stereoscopic; Digital Rapids StreamZHD v.3.7.2.25.