FLV demuxer / remuxer? (Details of my predicament inside)

[Colmino]

Here's the deal. All I'm trying to do is get a given FLV's audio extracted and replaced with different audio. I've thus far taken the circuitous route of locating a high-quality OGM source, converting it to raw video with Premiere and the Avisynth Premiere plugin, and encoding that as FLV. Unfortunately, Riva FLV Encoder apparently has a bug which causes the audio and video to lose sync, which it regains every 90 seconds or so with a loud static pop and/or a tiny pause in the video (in the same places every time, and regardless of the player). Not acceptable. (Yes, the encode fps I choose is identical to that of the raw video.)

Since demuxing and remuxing involves no video quality loss, that's the route I want to take with this project. But I don't know what app can do this with FLV, nor, it must be admitted, what steps would be needed. Help would be appreciated. Thanks!

[hech54]

Unfortunately, Riva FLV Encoder apparently has a bug which causes the audio and video to lose sync

With all of those steps prior to encoding with Riva....you are going to blame Riva?
I do all of my audio replacement with Virtualdub, output as uncompressed .avi then convert to .flv with Riva and no issues whatsoever.

[Colmino]

I'll put it this way. 1) When I play the raw video back, everything's fine. 2) Other people have also reported sync problems with Riva's output (try a longer video).

I'm sure it's possible to demux a FLV. This isn't some alien technology.

[hech54]

I'm sure it's possible to demux a FLV. This isn't some alien technology.

After you convert the video to something else...yes.

[Colmino]

Actually, it seems that DEmuxing a FLV is common. It's the recombination of audio+video -> FLV that seems to be elusive.

This is a lot of hoops I'm having to jump through just to get stereo audio on Youtube.

[hech54]

I recently used SUPER to convert an .flv file to something workable...it worked well.

[mgh]

FLV Extract will demux both flv1 and flv4 files. You can mux to flv using ffmpeg.

[Colmino]

Would you happen to recall the syntax for accomplishing the muxing of an FLV file from, say, audio.wav and video.whatever? It's not terribly clear in the documentation.

[Colmino]

Also.. FLV Extract seems to be one of those programs which for some reason requires the Microsoft .NET Framework 2.0. I've got this. But it also complains about a need to modify the security configuration, and fails to work without this having been done. What can I say? To me, all the .NET framework is is an annoyance which I must occasionally have in place to cover the needs of some atypically-coded app. I know NOTHING of what this thing is wanting, and clearly lack the ability to even perform a proper search on the matter.

It's almost hard to believe that all I want is to split an FLV into its audio and video components, replace the audio, and rejoin into a valid FLV.

[mgh]

maybe you need to run it as administrator. flv extract is the only program afaik
syntax for muxing
ffmpeg -i "xxx.avi" -vcodec copy -i "xxx.mp3" -acodec copy "xxx.flv"

[Colmino]

Alright. I determined that AviDemux can separate my FLV file just fine. It does not reencode or generate new data. The result is an mp3 (plays fine) and a video file of some sort which also plays fine, albiet naturally without audio.

The command line syntax you recommended seems to work, but the result is not playable. WMP locks up (requiring a task cessation), and FLV Player plays audio with no video. This happens even when I combine the original constituent pieces back together, rather than my own replacement audio.

So the lone remaining task, it seems, is to find an alternative to FFMpeg which performs as described, to mux the audio and video of a FLV back into a usable FLV.

[Colmino]

Also, it seems that all of these programs which are capable of generating FLV files rely upon FFMpeg, and FFMpeg keeps having the same exact issue: "non monotone timestamps" every ~95 seconds of video - an error which generates an audible pop and a brief video corruption. Strange that Premiere Pro doesn't exhibit these anomalies. Or whatever software is used on Youtube's servers, for that matter.

[Colmino]

Anyway, I invite anyone to try grabbing a Youtube .FLV of their choice, splitting it into audio and video (I use AviDemux), rejoining the parts with FFMpeg, and seeing how it works out for you. AviDemux sure doesn't much like the result. Gives me an essentially featureless green box as the video for the entire length.

[mgh]

suggest you try- load flv in AviDemux-set both video and audio to copy,format avi-save the avi. Load avi in virtualdubmod -set video to direct stream copy-streams-streamlist-click disable-click add and add the mp3 file you want. File-Save as and save new avi.
Then
ffmpeg -i "new.avi" -vcodec copy -acodec copy "new.flv"

edit-no need to use ffmpeg

load new.avi in AviDemux-set both video and audio to copy, format flv-save

[zugol]

Also.. FLV Extract seems to be one of those programs which for some reason requires the Microsoft .NET Framework 2.0. I've got this. But it also complains about a need to modify the security configuration, and fails to work without this having been done. What can I say? To me, all the .NET framework is is an annoyance which I must occasionally have in place to cover the needs of some atypically-coded app. I know NOTHING of what this thing is wanting, and clearly lack the ability to even perform a proper search on the matter.

It's almost hard to believe that all I want is to split an FLV into its audio and video components, replace the audio, and rejoin into a valid FLV.

You may try Avinaptic instead of FLV Extract. I used it to demux a mp3 from a FLV without video, worked great.
https://www.videohelp.com/tools/avinaptic