I wanted to share some solutions I have found regarding the codec issue:
I use Adobe products to create and edit video, and although they list h.264 as a rendering option, the resulting file is either an .mp4 or an .m4v, not an .h264. I haven't found any way to directly create a file with .h264 as the file extension with my video editing software. From what I can tell, .m4v is the closest to being a true avc/h.264 file that you can create with Adobe. And if you are using Adobe programs to render, the only way I have found to create an .m4v is to choose "H.264 Blu-Ray" as the output module. Unfortunately, that choice limits your options as far as image size and fps, which may or may not be a problem depending on whether the option you want is there (the choices are all HD, and sometimes 29.97 fps is not an option, such as with 720p, where you can only choose 59.97 fps or 24 fps). The m4v extension runs successfully on hello_video, by the way.
The other solution I found is to use a free program called "Yamb", which seems to be similar to what Dom was talking about, except it can not only extract a raw .h264 file from an .mkv, but also from an mp4. On their own, I cannot get mp4's to work on hello_video, but when I split the mp4 file with Yamb, I get an .h264 file and an .aac file. This makes it possible for me to render in mp4, which gives me more options (such as 29.97 fps at 720p, which I render as a lossless .avi in After Effects, and then use Adobe Media Encoder to create the .mp4, before stripping away the container using Yamb. If anyone knows a more direct way to get this done, I'm interested.).
Also, it is important to know that if you are trying out different file extensions to see what will work --getting them onto the SD card via FTP-- sometimes things will fail for some reason just because the last thing you tried was incompatible, and you could test several more things with false results. This can only be fixed by restarting your Pi and trying again. So if you are trying out specific render settings to see which exact ones work, keep in mind that you need to reboot after failed attempts if you want to be sure about whether they work.