Splitting 5.1 audio into discrete AAC streams is broken in FFmpeg

[Bryan Bortz]

Up until FFmpeg v4.0 I have been able to run the following command on an input video file that contains an H.264 video track and either AC3 or DTS audio stream and produce an MP4 that has 6 streams of audio. Each stream corresponds to a channel of the 5.1 audio.

ffmpeg -i INPUT.MKV -vcodec copy -filter_complex channelsplit=channel_layout=5.1 -acodec aac -movflags faststart OUTPUT.MP4

It even worked on Stereo tracks and put the L and R channels into the proper places and produced some extraneous silent tracks for the other 4 channels.

But now in v4.0.1 I get the following error:

[aac @ 0x7f7f65001e00] Unsupported channel layout

Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

Conversion failed!

Changing the command to be the following does not improve things:

ffmpeg -i INPUT.MKV -vcodec copy -filter_complex "channelsplit=channel_layout=5.1[FL][FR][FC][LFE][BL][BR]" -acodec aac -movflags faststart OUTPUT.MP4

It gives the following error:

Filter channelsplit:BR has an unconnected output

(Note that BL/BR and SL/SR both produce the same error about BR)

This MP4 file structure is useful for playing back inside of Unity with virtual speakers placed in the environment.

My end goal:

• MP4 (MOOV Atom at the Front)

-H.264 Video Stream
-AAC Audio Stream - FL
-AAC Audio Stream - FR
-AAC Audio Stream - FC
-AAC Audio Stream - LFE
-AAC Audio Stream - SL
-AAC Audio Stream - SR

[Bryan Bortz]

-report log

[Carl Eugen Hoyos]

How is the issue you see related to the log you attached?

Please test current FFmpeg git head and provide the command line you tested together with the complete, uncut console output to make this a valid ticket.

[Bryan Bortz]

-report log - Previous log was not the correct log!

[Bryan Bortz]

@cehoyos Sorry about that! I grabbed the wrong -report log!

The correct log (ffmpeg-20180620-121649.log​) Is now attached.

ffmpeg -i /Users/bryan.bortz/Movies/the_gate-1987-intro.mp4 -vcodec copy -filter_complex channelsplit=channel_layout=5.1 -acodec aac -movflags faststart -report output-test.mp4

[Bryan Bortz]

I am also attaching a log from v3.4.2 where the same command succeeds and provides the desired and expected output:

ffmpeg-20180620-122243-v3.4.2.log

[Bryan Bortz]

-report of the command working on v3.4.2

[Carl Eugen Hoyos]

Regression since fbf295e2bd4d48d7a0a094ed5afce2fa5b6cf35a
Please confirm that the issue was also reproducible with FFmpeg 4.0.

[Bryan Bortz]

Can confirm the behavior exists in FFmpeg 4.0. (additional log attached: ffmpeg-20180620-165657-v4.0.log)

[Bryan Bortz]

-report FFmpeg v4.0

[Elon Musk]

This is usage issue. You need to add to every single output of your filtergraph aformat=channel_layouts=mono and properly map them to output.

AAC with PCE can not encode FL/FR/SL/SR/.. channel layouts, so you need to convert each stream to mono channel layout.

[Bryan Bortz]

Replying to richardpl:

This is usage issue. You need to add to every single output of your filtergraph aformat=channel_layouts=mono and properly map them to output.

AAC with PCE can not encode FL/FR/SL/SR/.. channel layouts, so you need to convert each stream to mono channel layout.

Can I request an example? I've been playing around with this for a while now and can't find any examples/docs specifically about this case. Various things I try work in versions less than 4.0 but not in 4.0+.

Thank you.

[Elon Musk]

"channelsplit=channel_layout=5.1[FL][FR][FC][LFE][BL][BR],[FL]aformat=channel_layouts=mono[FL];[FR]aformat=channel_layouts=mono[FR];[FC]aformat=channel_layouts=mono[FC];[LFE]aformat=channel_layouts=mono[LFE];[BL]aformat=channel_layouts=mono[BL];[BR]aformat=channel_layouts=mono[BR]"