FFMPEG Remove single audio channel AC3

[rushmusashi]

Hello everybody, I have videos that I am trying to batch edit with ffmpeg, I'm only trying to modify the audio track and remove the 6th channel and only have 5 channels.


I would also possibly like to just merge the 3rd and 4th channel into one and just leaving 5 total channels.


Most of the time no matter what I try it leaves all 6 channels and just blanks one out for some reason

I've tried different versions of FFMPEG, differentfilters and -af, -filter_complex, -filter:a, channelmap, channel_layout, pan, they all do the same thing


So far the only thing that really works is converting the audio to a wav file, but you'd think AC3 or AAC would be able to do it as well

for %%g in (*.mkv) do ffmpeg -i "%%g" -map 0:a:0 -af channelmap=channel_layout=5.0 -c:a pcm_s16le "%%~ng.wav"

Using -filter:a "channelmap=channel_layout=4.0" does create 4 channels, but I'm wanting 5


Even trying AAC does the same thing and leaves just an empty channel

for %%g in (*.mkv) do ffmpeg -i "%%g" -map 0:v -map 0:a:0 -sn -c:v copy -filter:a "channelmap=channel_layout=5.0" -c:a aac "%%~ng.mp4"

[pandy]

It is unclear to me channel layout you are trying to achieve?

Instead numbers use channel names, please use ffmpeg naming convention provided below:

Individual channels:
NAME           DESCRIPTION
FL             front left
FR             front right
FC             front center
LFE            low frequency
BL             back left
BR             back right
FLC            front left-of-center
FRC            front right-of-center
BC             back center
SL             side left
SR             side right
TC             top center
TFL            top front left
TFC            top front center
TFR            top front right
TBL            top back left
TBC            top back center
TBR            top back right
DL             downmix left
DR             downmix right
WL             wide left
WR             wide right
SDL            surround direct left
SDR            surround direct right
LFE2           low frequency 2
TSL            top side left
TSR            top side right
BFC            bottom front center
BFL            bottom front left
BFR            bottom front right

Standard channel layouts:
NAME           DECOMPOSITION
mono           FC
stereo         FL+FR
2.1            FL+FR+LFE
3.0            FL+FR+FC
3.0(back)      FL+FR+BC
4.0            FL+FR+FC+BC
quad           FL+FR+BL+BR
quad(side)     FL+FR+SL+SR
3.1            FL+FR+FC+LFE
5.0            FL+FR+FC+BL+BR
5.0(side)      FL+FR+FC+SL+SR
4.1            FL+FR+FC+LFE+BC
5.1            FL+FR+FC+LFE+BL+BR
5.1(side)      FL+FR+FC+LFE+SL+SR
6.0            FL+FR+FC+BC+SL+SR
6.0(front)     FL+FR+FLC+FRC+SL+SR
hexagonal      FL+FR+FC+BL+BR+BC
6.1            FL+FR+FC+LFE+BC+SL+SR
6.1(back)      FL+FR+FC+LFE+BL+BR+BC
6.1(front)     FL+FR+LFE+FLC+FRC+SL+SR
7.0            FL+FR+FC+BL+BR+SL+SR
7.0(front)     FL+FR+FC+FLC+FRC+SL+SR
7.1            FL+FR+FC+LFE+BL+BR+SL+SR
7.1(wide)      FL+FR+FC+LFE+BL+BR+FLC+FRC
7.1(wide-side) FL+FR+FC+LFE+FLC+FRC+SL+SR
7.1(top)       FL+FR+FC+LFE+BL+BR+TFL+TFR
octagonal      FL+FR+FC+BL+BR+BC+SL+SR
cube           FL+FR+BL+BR+TFL+TFR+TBL+TBR
hexadecagonal  FL+FR+FC+BL+BR+BC+SL+SR+TFL+TFC+TFR+TBL+TBC+TBR+WL+WR
downmix        DL+DR
22.2           FL+FR+FC+LFE+BL+BR+FLC+FRC+BC+SL+SR+TC+TFL+TFC+TFR+TBL+TBC+TBR+LFE2+TSL+TSR+BFC+BFL+BFR

[rushmusashi]

It is unclear to me channel layout you are trying to achieve?

Instead numbers use channel names, please use ffmpeg naming convention provided below:

Thanks for replying. I was just looking for any working 5 channel setup, I've been trying to put in many different layouts but it doesn't seem to alter the audio properly.

I guess 5.0(side) looks like it should work, but I've tried putting that in different ways as well and it doesn't seem to make the proper changes.

I was just playing around with it some more and found that it seems to work if I output the audio to an AC3 file, but it does not work when outputting to an mkv or mp4 file for some reason. I can make that work I guess and just batch process them into ac3 files and then batch remux them into new video files with those audio files, but you'd think you should be able to just do it in one go.

After looking at it I'm thinking the best thing to do would be to just combine the 3rd and 4th channels into one and leave the others intact, so not sure how to do that exactly.

[ProWo]

pan=5.0

[rushmusashi]

pan=5.0

Thanks, but that does nothing lol, only putting that in just created 6 empty channels in an mkv or mp4, trying to create an AC3 file made 5 empty channels

[rushmusashi]

So I also have been playing around with the PAN filter before ProWo commented.

Putting in this actually created the correct AC3 file that I'm looking for, but it does not work in an MKV or MP4, so I don't know what's up with it, maybe a bug in ffmpeg.

for %%g in (*.mkv) do ffmpeg -i "%%g" -map 0:a:0 -af "pan=5.0(side)|c0=FL|c1=FR|c2=FC+LFE|c3=SL|c4= SR" -c:a ac3 "%%~ng.ac3"

c0 1 2 3 4 5 would be the 6 audio channels for 5.1 (side) (FL+FR+FC+LFE+SL+SR)

so I just combined the 2 center channels into 1 channel, the 3rd channel for 5.0(side) c2=FC+LFE

[ProWo]

This commandline gives a 5 channel ac3.

ffmpeg -i input.mkv -map 0:x -af "pan=5.0|c0=c0|c1=c1|c2=c2|c3=c3|c4=c4" -c:a ac3 output.ac3

(where x is the desired audio stream, e.g. 2)


[Attachment 74461 - Click to enlarge]

No problem at all for muxing this ac3 to m4 or mkv.

[rushmusashi]

This commandline gives a 5 channel ac3.

ffmpeg -i input.mkv -map 0:x -af "pan=5.0|c0=c0|c1=c1|c2=c2|c3=c3|c4=c4" -c:a ac3 output.ac3

(where x is the desired audio stream, e.g. 2)


No problem at all for muxing this ac3 to m4 or mkv.

Thanks. I used -map 0:a:0 because there are 2 audio tracks in the videos and I only want to reencode the first one.

The commandline I posted looks to work perfect for making the right 5 channel audio ac3 file from the 6 channel.

The problem I'm running into is that it won't encode it directly from the mkv into the new mkv or mp4, so I will have to do it all the harder way and create all ac3 files and then remux them into the videos, there's around 300 videos, that's why I was trying to get a proper batch script lol. I'll just have to do it all with 2 batch scripts instead of one, there must be a bug somewhere in something.