Losslessly demux elementary streams

[SameSelf]

I am sure this has been asked before, so my apologies in advance. On one level I think it is a simple question, but at the same time maybe not. My workflow involves encoding elementary .264 streams and .aac streams separately. I then mux them using mp4box. But sometimes, for various reasons, I feel a need to demux the resulting mp4. Is there a method to do this losslessly back to .264 and .aac? ffmpeg? mp4box?

I found the following for MP4Box documentation which makes me think otherwise:

The input file must have enough random access points in order to be splitted. This may not be the case with some video files where only the very first sample of the video track is a key frame (many 3GP files with H263 video are recorded that way). In order to split such files you will have to use a real video editor and re-encode the content.

Thanks as always.

[poisondeathray]

Yes you can use ffmpeg, mp4box etc... to demux

It's "lossless" in the sense that decoded image is lossless. But there are stream sequence headers, +/- metadata that are lost when you mux and demux. Normally not a problem for most scenarios, but in strict BD authoring , some strict programs will complain. Basically never put it in a container for strict BD authoring

[SameSelf]

Ahh, now I understand. I will definitely make note of that. My mp4 muxes are for Youtube, so I don't worry about keeping them BD compliant. But that is probably an oversight on my part. Which reminds me as an Encore user, I need to look again into purchasing DVD Architect.

[poisondeathray]

Encore and DVDA usually don't care about those things. I'm talking about strict BD authoring

[SameSelf]

As in like Scenarist?

[poisondeathray]

Yes, scenarist, dostudio, blu-print will complain - basically the super strict authoring tools capable of making images for replication

[SameSelf]

I see, thanks as always!

[_Al_]

mp4box can mux just video track from one video and audio from other video, if that is the case:

MP4box.exe -add "video1.mp4"#video  -add "audio.m4a" -new "new_out.mp4"
or
MP4box.exe -add "video1.mp4"#video  -add "video2.mp4"#audio -new "new_out.mp4"