Well, MLB finally released more of the video clip. You can find it here on their YouTube channel. The video is nearly three and a half minutes long, however you can clearly see the video is edited down in a certain part. More after the jump.
Watching the clip, you can see that at the 1:31 mark the video is cut down. This is most likely the removal of the delay caused by the groundscrew keeping Kuhn and Vice President Gerald Ford off the field. There are also some cuts during the 'backslaps' Aaron gets in the dugout, which excludes the Cincinnati police officer bringing the ball to Aaron in a brown paper bag.
What is interesting to note is that this clip is even cut down. In the original post that highlighted MLBNetwork footage, this shot of Aaron on deck/coming to the plate was originally in it.
Hamilton was the radio broadcaster for the Braves until the 1975, not on television. His descriptions here make it pretty clear he is giving a radio account of the events anyways. WLWT, the Reds flagship did not broadcast their first game of the 1974 season until April 14th. Every record I have found does not show this to be a NBC broadcast, as a) there is no banner in foul territory and b) it isn't shown in the television listings. This could be a WCTG-TV broadcast, however with the radio over top it makes it hard to determine.
The production value, with the cameras taking shots of Aaron on-deck, the CF camera, etc makes me believe it is from a television broadcast.
There is one last possibility. This could actually be NBC footage, however not an NBC broadcast. On the day that Aaron hit the homerun, it was unclear whether he would be in the lineup or not. NBC did not show the game live. However, they did cut into their mid-afternoon soap operas to show a replay of Aaron's 714th homerun. This surviving footage could actually be from that replay.
As I said before, at the time, this game SHOULD have been recorded until Aaron took his last at-bat. At any point in this game, Aaron could have hit 715 making every at-bat potentially historic.
It is great of MLB to put clips like this out. Hopefully they feel it worthwhile to start putting up the plethora of partial games they have on their YouTube channel.