I need to attach audio to a video I am editing. I imported a video as an MPEG-4 and added MP3 audio to go with it and its 100% quality in the preview box as it originally was. When I render this though I tried FLV because I don't know what alot of the other formats do or how they playback so when it finished huge pixelization occured in the scene where certain gradients and fast moving objects are in the video. I did not try to export as another MP4 due to After Effects telling me it would resize the video to a smaller dimension size so I did FLV.
What I want to understand is that if After Effects can strip down frame by frame the MP4 video and re-compile it with the same quality of the frames. The quality of the video looks flawless already as an MP4 since it was made as an MP4 with a 3D program but I don't get why After Effects must reduce the quality even more.
I have all the time in the world so if you tell me the slowest method but it keeps the quality the same please do tell.
My computer stats is well above required to run After Effects and I am using CS6.