user2247: Is there any way to swap out the audio track on a rendered H.264 MPEG-4 without having to re-render the entire video project? Can this be done with Premiere, MPEG Streamclip, ffmpeg, or some other tool that I'm not familiar with ?
I have a long video project that took many hours to render, and I would like to swap out the audio (minor mixing changes) without having to re-render the entire video project. The new audio is exactly the same length.
Is this feasible? I'm primarily a Premiere user, but I'm happy to hear solutions for other tools.

user3908: Yes, ffmpeg can do what you need, which is to demux the MP4 into audio and video components, then remux using the new audio. Actually, you can extract just the video since you don't need the existing audio. I'm not an expert in ffmpeg, but the demux command line would be something like ffmpeg -i myfile.mp4 -vcodec copy myvideo.h264. 

user6615: ffmpeg is a good choice for this task. You can do this with this command:
ffmpeg -i input.mp4 -i input_audio.aac -map 0:0 -map 1 -vcodec copy -acodec copy output.mp4


2247: <p>Is there any way to swap out the audio track on a rendered H.264 MPEG-4 without having to re-render the entire video project? Can this be done with Premiere, MPEG Streamclip, ffmpeg, or some other tool that I'm not familiar with ?</p>

<p>I have a long video project that took many hours to render, and I would like to swap out the audio (minor mixing changes) without having to re-render the entire video project. The new audio is exactly the same length.</p>

<p>Is this feasible? I'm primarily a Premiere user, but I'm happy to hear solutions for other tools.</p>
 3908: <p>Yes, ffmpeg can do what you need, which is to demux the MP4 into audio and video components, then remux using the new audio. Actually, you can extract just the video since you don't need the existing audio. I'm not an expert in ffmpeg, but the demux command line would be something like <strong><em>ffmpeg -i myfile.mp4 -vcodec copy myvideo.h264</em></strong>. </p>
 6615: <p>ffmpeg is a good choice for this task. You can do this with this command:</p>

<pre><code>ffmpeg -i input.mp4 -i input_audio.aac -map 0:0 -map 1 -vcodec copy -acodec copy output.mp4
</code></pre>
