Question / Help Simple questions about OBS Studio's 'Remux'

vencabot

Member
I'm relatively new to video-editing and am only somewhat confident in my understanding of the term 'remux'. In my case, I have .flv files recorded by OBS Studio, and I'm using its built-in Remux tool to convert them to MP4.

As I understand it, the Remux tool is simply changing the container of the underlying video and audio data from FLV to MP4 without re-encoding either the video or audio -- which is great, because that should mean that there is no degradation in quality, right?

What confuses me, though, is that it's still a 20-minute operation on an hour-and-a-half recording (recorded at a high bitrate of 30Mbps, given). If it's just moving some meta-data around (changing the container?), why does it take more than a second?

Also, when it creates the remuxed MP4 file, is the moov atom placed at the start of the file (good for YouTube) or saved to the end of the file (OBS Studio's typical MP4 recording behavior, since, obviously, it doesn't know how long the file is going to be until it finishes recording)?

Thank you for your insight!
 

Harold

Active Member
What confuses me, though, is that it's still a 20-minute operation on an hour-and-a-half recording (recorded at a high bitrate of 30Mbps, given). If it's just moving some meta-data around (changing the container?), why does it take more than a second?
It's not quite JUST moving metadata around, and you are still dealing with hard drive random seek limits when doing this process.
 

vencabot

Member
Thank you for your insight and patience, Harold! I'm happy to know that there's really no encoding going on. As for HDD seeking, I realized immediately after my post that I should've probably sent the remuxed file to a different drive than the source FLV. Probably would've helped somewhat.

If you find that you have a few moments and don't mind educating a noob, I'd love to hear more about what sorts of stuff is happening during the remux process. I've found that wikis and stuff are a bit difficult to parse.

Anyone know about whether the remuxed MP4 has its moov atom at the start or finish? If not, I'll do some tests and report back in a couple days; I was just hoping somebody knew off the top of their head.
 

vencabot

Member
[EDIT] Even with MP4 files where I've manually moved the moov atom to the beginning of the file using ffmpeg, YouTube complains about the MP4 not being 'streamable,' which I had been using for my metric -- so maybe OBS Studio's Remux DOES put the moov atom at the beginning. Uploading MP4s takes longer, but produces YouTube videos with seek-thumbnails when hovering the mouse over the seek bar. FLV takes less time to process but has no seek thumbnails, which is unacceptable. I'm gonna try uploading an MKV file next. God, I hate Youtube.

The Remuxed FLV->MP4 files that OBS Studio's tool produces seem to have their moov atom located at the end of the file, just as if you'd recorded directly to MP4. Bummer! There are benefits to recording as FLV, but I was hoping that the remuxer would put the moov atom at the front, since this is what YouTube and other streaming media players want. v_v
 
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