[FFmpeg-user] Channel manipulation and audio filter equivalencies
Hi! (First time post on this list.) I'm not a hugely skilled audiophile, and I'm trying to do some audio manipulation with ffmpeg. At times, the result isn't what I'd like it to be, and I'm not always sure why, so the first step right now is to try to understand what on earth it is that I'm actually asking ffmpeg to do :) Primary references: https://trac.ffmpeg.org/wiki/AudioChannelManipulation https://ffmpeg.org/ffmpeg-filters.html My input file has eight audio channels and is described by ffprobe as "7.1". If I use the channelsplit filter, I can listen to any channel individually: ffmpeg -loglevel error -stats -y -i Original.mkv -filter_complex 'channelsplit=channel_layout=7.1' -map 0:v -map 0:s channel_split.mkv (Without loglevel error, this produces massive spam of "Queue input is backward in time", but the audio is fine. As a side point, I'm curious as to whether there's a better solution than simply silencing those warnings.) The result is a file with video and subtitle streams unchanged, and eight individual audio streams. With judicious use of "-metadata:s:a:%d" these can even be labelled, making them easy to flip through. Well and good. The real challenge is selecting two channels and trying to make them into the left and right channels of a new stereo audio channel. One option is channelmap: ffmpeg -loglevel error -stats -y -i Original.mkv -af 'channelmap=map=BL|BR' channel_split.mkv Another option is pan: ffmpeg -loglevel error -stats -y -i Original.mkv -af 'pan=stereo|c0=BL|c1=BR' channel_split.mkv According to the docs, pan should detect a pure channel mapping and do an optimized lossless remap, which in theory should mean that these two are the same. But my understanding must be wrong, because they sound completely different :) A third option is join: ffmpeg -loglevel error -stats -y -i Original.mkv -af 'join=inputs=1:map=0.BL-FL|0.BR-FR' channel_split.mkv This sounds very similar to the pan result, but quieter. What am I doing wrong with the channelmap, and what is the preferred way to create a stereo output by selecting channels? Chris Angelico ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
On Fri, Nov 6, 2020 at 2:43 AM Chris Angelico wrote: > The real challenge is selecting two channels and trying to make them > into the left and right channels of a new stereo audio channel. One > option is channelmap: > > ffmpeg -loglevel error -stats -y -i Original.mkv -af > 'channelmap=map=BL|BR' channel_split.mkv > > Another option is pan: > > ffmpeg -loglevel error -stats -y -i Original.mkv -af > 'pan=stereo|c0=BL|c1=BR' channel_split.mkv > Anyone have recommendations on these options, or any other preferred way to remap channels at maximum quality? ChrisA ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
> On 12 Nov 2020, at 06:10, Chris Angelico wrote: > > Anyone have recommendations on these options, or any other preferred > way to remap channels at maximum quality? You could try using the channelsplit and selecting the specific channels you want and then merging them into a single stream. channelsplit=channel_layout=7.1:channels=LF|RF[lf][rf];[lf][rf]amerge=inputs=2[aout] Thanks Adam ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
On Thu, Nov 19, 2020 at 8:48 AM adam smith via ffmpeg-user wrote: > > > > On 12 Nov 2020, at 06:10, Chris Angelico wrote: > > > > Anyone have recommendations on these options, or any other preferred > > way to remap channels at maximum quality? > > You could try using the channelsplit and selecting the specific channels you > want and then merging them into a single stream. > channelsplit=channel_layout=7.1:channels=LF|RF[lf][rf];[lf][rf]amerge=inputs=2[aout] > Hmm, I must be missing something here, because I get this error: $ ffmpeg -stats -y -i Original.mkv -filter_complex 'channelsplit=channel_layout=7.1:channels=LF|RF[lf][rf];[lf][rf]amerge=inputs=2[aout]' -map 0:v -map 0:s channel_split.mkv [AVFilterGraph @ 0x559f11cf7f80] Error initializing filter 'channelsplit' with args 'channel_layout=7.1:channels=LF|RF' Error initializing complex filters. Invalid argument But when I tried things along these lines, I got complaints that some of the outputs weren't connected to anything. ChrisA ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
> On 18 Nov 2020, at 21:55, Chris Angelico wrote: > > But when I tried things along these lines, I got complaints that some > of the outputs weren't connected to anything. I didn’t add the input stream as I am not sure what stream it is on your source. If could be something like… ffmpeg -stats -y -i Original.mkv -filter_complex "[0:1]channelsplit=channel_layout=7.1:channels=LF|RF[lf][rf];[lf][rf]amerge=inputs=2[aout]" -map 0:v -map "aout" -map 0:s channel_split.mkv ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
On Thu, Nov 19, 2020 at 9:21 AM adam smith via ffmpeg-user wrote: > > > > On 18 Nov 2020, at 21:55, Chris Angelico wrote: > > > > But when I tried things along these lines, I got complaints that some > > of the outputs weren't connected to anything. > > I didn’t add the input stream as I am not sure what stream it is on your > source. > If could be something like… > > ffmpeg -stats -y -i Original.mkv -filter_complex > "[0:1]channelsplit=channel_layout=7.1:channels=LF|RF[lf][rf];[lf][rf]amerge=inputs=2[aout]" > -map 0:v -map "aout" -map 0:s channel_split.mkv > Regardless of the input mapping, it's still complaining about that channelsplit configuration. Is there any way to figure out what the actual error is? Even with loglevel debug, all I get is this: Successfully opened the file. [Parsed_channelsplit_0 @ 0x55f0a8d38780] Setting 'channel_layout' to value '7.1' [Parsed_channelsplit_0 @ 0x55f0a8d38780] Setting 'channels' to value 'LF|RF' [AVFilterGraph @ 0x55f0a8cea280] Error initializing filter 'channelsplit' with args 'channel_layout=7.1:channels=LF|RF' Error initializing complex filters. Invalid argument ChrisA ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
Apologies, I said LF|RF but it should be 'channelsplit' with args 'channel_layout=7.1:channels=FL|FR’ "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"], > On 18 Nov 2020, at 22:47, Chris Angelico wrote: > > 'channelsplit' with args 'channel_layout=7.1:channels=LF|RF' ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
On Thu, Nov 19, 2020 at 10:08 AM adam smith via ffmpeg-user wrote: > > Apologies, I said LF|RF but it should be > 'channelsplit' with args 'channel_layout=7.1:channels=FL|FR’ > > "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"], > Ahh, thank you! That does at least work, so now I'm going to let that do some work for a while and then listen to the results :) Appreciate the help. Still not sure how all the different filters behave. ChrisA ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] Channel manipulation and audio filter equivalencies
> On 18 Nov 2020, at 23:29, Chris Angelico wrote: > > Appreciate the help. Still not sure how all the different filters behave. No worries, I have not read any of the code so I do not really know what manipulations are occurring under the hood. As far as I can tell, the channel split is pulling the individual channels from the source audio stream and the amerge is combining them into a new stereo stream basically unchanged other than any codec transformations. Using the pan filter would allow you to manipulate the actual audio content as it allows for each channel pan level and attenuation; this could affect audio quality perhaps. As I say, this is not based on reading one reading any code so I may be wrong. I will be interested to know your results. Thanks Adam ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
