Explanation of Audio Filters please?

[Legin777]

I have a video file that I want to convert to AC-3(lav) 640kbps. The default mixer option in the filter tab of the audio output section seems to be set to Stereo. Will I still get the 6 channels when the audio is passed through my receiver or do I need to tick remix and select 5.1 - I am a newbie so would appreciate a proper understanding of the difference between the two settings please?

[eumagga0x2a]

Settings in the audio output tab of the Preferences affect the playback in Avidemux only, not related to filtering eventually enabled when re-encoding audio.

I have a video file that I want to convert to AC-3(lav) 640kbps.

Just raw audio? No video? What are the properties (codec, number of channels, eventually also the sampling frequency) of the audio track of the source video?

[Legin777]

I am converting the audio section only of a video file (copying the video) from EAC-3 6 channel bitrate 7768 kbs sampling rate 48.0 Khz to AC-3(lav) 640kbs. Are you saying that the CONFIGURE and FILTER settings of the audio output section have no affect on the saved converted file?

[eumagga0x2a]

Are you saying that the CONFIGURE and FILTER settings of the audio output section have no affect on the saved converted file?

Settings in the audio output tab of the Preferences

...have no effect on the saved converted file. I didn't mention the audio encoder configuration and audio filter either in the main window or in the "Select audio track" dialog. Of course, they are responsible for the actual output when exporting (saving) a file.

If your receiver doesn't support E-AC3, then yes, you need to re-encode into the plain old AC3. You don't need any filtering for this particular use case.

[eumagga0x2a]

By the way, you don't specify the version of Avidemux you refer to, but I would strongly recommend using the latest 2.8.1 nightly build rather than the 2.8.0 release due to important bug fixes and enhancements (especially in the section of audio filters, courtesy of szlldm) which happened after the last release.

https://avidemux.org/nightly/

[Legin777]

I have downloaded 2.8.1 thanks. Just to clarify, is there any difference to the saved file in terms of the audio quality my 5.1 receiver will reproduce if I apply 5.1 rather than Stereo in the audio encoder filter remix option at the conversion stage, or is all the same data still there and just hidden in the stereo format, and what is the purpose of the no change option, because it caused my 2.8.0 version of avidemux to freeze when I try it out? Thanks in advance

[eumagga0x2a]

Please, if the source has 6 channels (5.1), you add none audio filters at all, period. No remixing, no resampling, really none.

The freeze of 2.8.0 was probably entirely unrelated to audio. Please retry with 2.8.1 nightly and if the freeze persists, then we'll have to analyze the reasons.

Downmix to Stereo is entirely irreversible.

[Legin777]

In wiki user instructions it states:

The mixer will change the number of channels that you hear. The most common usage is to go from 5.1 sound to stereo. You will probably want Dolby Pro Logic II downmixing. Beware that to be efficient, Dolby Pro Logic audio must not be encoded with a low bitrate (~(nbsp)<(nbsp)160(nbsp)kb/s).

Please review the attached screenshot which is without changes. Although Stereo is selected by default, it is grayed out and the remix box is unchecked. Does this mean that it is not remixing it down to stereo?

[eumagga0x2a]

Correct, the mixer in audio filters is disabled as it should be for your purposes.

Is the freeze you experienced with 2.8.0 gone in this 2.8.1 nightly?

[Legin777]

The freeze (file crash) is still there in 2.8.1, but it is probably something I am doing wrong. Instead of leaving the remix option in the audio filter section alone (unchecked), I ticked the box and selected the option no change. I assume it does what it says on the tin, but actually, you have explained that if I leave the audio filter section alone, there will be no change anyway to the audio affected by the choices in that section.

[eumagga0x2a]

The freeze (file crash) is still there in 2.8.1

Please launch Avidemux 2.8.1 nightly, reproduce the crash, then attach admlog.txt from %localappdata%\avidemux\ to your reply. Do not restart Avidemux prior to having copied admlog.txt to a different location else it will be overwritten.

Instead of leaving the remix option in the audio filter section alone (unchecked), I ticked the box and selected the option no change.

Well, it is a fancy way to do nothing (or more precisely, this option tells the audio filter mixer to copy input data without changes to the output buffer instead of not creating the filter instance in the first place).