Re-Muxing DTS to AC3

[Ronstang]

I'm new to doing this and have been an avid avidemux user over the years so this seems a strong option.  I tried it and it worked quickly and resulting audio seems of quality I just want to understand what I am doing.  I picked the lav filter as I wanted a higher bitrate.

Does the lav encoder use VBR encoding for ac3?  I ask because I tried other utilities to do the same file as a comparison and those use ffmpeg, which is what I traditionally used for re-muxing while encoding, and I got a different file size for every single utility I tried on the same file using the same target bitrate.  I have been told that ffmpeg does not support VBR encoding so that does not explain the difference between the two options I tried using ffmpeg....same version that I have all my programs that utilize ffmpeg use. 

Is there a quality difference between lav and ffmpeg?  I'm simply trying to pick the best quality and then use the utility that I find the easiest.  I like avidemux and always have but it has no option for ffmpeg.

eumagga0x2a....I suppose there is a reason you chose lav of aften over ffmpeg.  I was just wondering if you could school me here.  Just trying to learn.

Thanks

[szlldm]

lav is ffmpeg

[Ronstang]

lav is ffmpeg

Learn something every day.  If that is the case I don't see ffmpeg anywhere in the Avidemux folder so where does it find the ffmpeg executable?  I have it in a folder under Program Files but it's been so long since I installed Avidemux that I don't remember pointing it there.  And if I had to point it to ffmpeg it is one sitting somewhere I forgot about and I need to switch it to the current build I just installed for comparison.

[szlldm]

parts of ffmpeg are integrated into Avidemux

[eumagga0x2a]

I may be wrong here, but AFAIK the ac3 encoder in libavcodec outputs CBR only.

If that is the case I don't see ffmpeg anywhere in the Avidemux folder so where does it find the ffmpeg executable?

lav (lavc, short for libavcodec) is a library belonging to the FFmpeg project. We use the functionality provided by the library (as well as by libavformat for muxing, libswscale for image conversion and libpostproc for post-processing, all of them using libavutil), not the frontend (ffmpeg, ffprobe and ffplay).

[Ronstang]

Great information thank you.

lav (lavc, short for libavcodec) is a library belonging to the FFmpeg project. We use the functionality provided by the library (as well as by libavformat for muxing, libswscale for image conversion and libpostproc for post-processing, all of them using libavutil), not the frontend (ffmpeg, ffprobe and ffplay).

So does that means that the version of ffmpeg is not kept as up to date in Avidemux?  I am using the latest build of ffmpeg to do the testing in other utilites so does that mean there is no way to do a real comparison.  Could that explain the difference in file sizes?  It's not huge, maybe 8-10%.  It's not the size as much as the quality that concerns me.

One extra question, is this encoding using CBR or VBR?  I'm not sure if ffmpeg can even do VBR in ac3 but I am a neophyte at best on these issues?.

[eumagga0x2a]

Currently we use libraries from FFmpeg 6.0.

AFAIK libavcodec supports only CBR for AC3. It doesn't matter what kind of application makes use of it – the tool "ffmpeg" from the FFmpeg project or some other application.

[Ronstang]

Nice! Then it is pretty up to date as I am using some build of version 6.0 so I don't understand the difference in file size, but I am not one who thinks bigger files mean better quality.  You have always provided a solid program so I trust your implementation....and the bonus is your program gets the job done quickly.

[eumagga0x2a]

I don't see a sufficient base for comparison. If you are very interested in identifying differences, please provide exact analysis of the source video and of both processed videos, given all have the same duration, as produced by MediaInfo, as well as complete uncut ffmpeg command line and the corresponding Avidemux project script.

I also don't quite understand the reason for encoding to AC3 in the first place – is it done due to some hardware not supporting AAC?

[sark]

We use the functionality provided by the library (as well as by libavformat for muxing, libswscale for image conversion and libpostproc for post-processing, all of them using libavutil), not the frontend (ffmpeg, ffprobe and ffplay).

Just curious.

So Avidemux borrows from ffmpeg for muxing, and does not have its own muxers, as recently suggested on another forum.

I also don't quite understand the reason for encoding to AC3 in the first place – is it done due to some hardware not supporting AAC?

Can't speak for the OP, but I create AVCHD output for disc. The authoring app I use, if provided with AAC, will reencode to AC3. Hence, an AC3 workflow, I can control, is preferred.

[eumagga0x2a]

This is mostly correct, only the AVI muxer (and "raw" video-only "muxer") is completely internally implemented. The deprecated MP4v2 muxer uses libmp4v2, other muxers let libavformat do all the magic.

Yes, such basically obsolete workflows.

[Ronstang]

OK, I have this figured out but now I am experimenting with AAC 5.1 encoding.  It appears to be VBR, which is great, but when choosing a bitrat....say 384, does that mean 384 is the max or the average since it is VBR?

[eumagga0x2a]

It should be the latter.

[Ronstang]

It should be the latter.

That is what I thought since the file size was almost exactly the same as ac3 384 and it wouldn't make sense for it to be that max as it should then have a smaller file size..  Thanks for confirming.