[FFmpeg-user] Decode ac3 from multichannel USB input
Fred Rotbart
rotbart at gmail.com
Fri Nov 3 14:03:06 EET 2023
Finally, I managed to extract ac3 from the Digiface USB spdif input but
not in a way that helped me.
It took a while but eventually I learned that the spdif signal is not
pure ac3 but ac3 wrapped as SMPTE ST 337. VLC does not recognise this
but ffmpeg and MediaInfo do.
So if I first capture the first two Digiface channels into a file using:
`ffmpeg -f avfoundation -i :2 -filter_complex "[0:a]pan=2C|c0=c0|c1=c1"
-y capture.wav`
and pipe this file into the VLC audio capture device via Blackhole2ch or
any other audio device:
`ffmpeg -y -i capture_2c.wav -f spdif -f audiotoolbox
-audio_device_index 2 -`
it works since ffmpeg will extract the ac3 and if necessary, decode
appropriately.
However, if I try to use VLC as the capture device directly:
`ffmpeg -f avfoundation -i :2 -filter_complex "[0:a]pan=2C|c0=c0|c1=c1"
-f spdif -f audiotoolbox -audio_device_index 2 -`
ffmpeg does not extract the ac3 but passes on the raw signal as PCM!
I tried bypassing the problem by using a pipe, such as:
`ffmpeg -f avfoundation -i :2 -filter_complex "[0:a]pan=2C|c0=c0|c1=c1"
-f s16le - | ffmpeg -i - -f audiotoolbox -audio_device_index 2 -`
Here after the pipe, ffmpeg recognised the format but this only worked
for about 15 seconds and then no more data was passed.
Nothing I tried solved this problem, so unless I get another bright idea
or some help, I guess I am giving up on this for now.
On 31/10/2023 17:39, Fred Rotbart wrote:
> Okay! After many hours I am making some progress (if anyone is
> interested).
>
> This extracts the channels, recognises the ac3 and decodes it but
> there are errors thrown from time to time and the rate is not constant.
>
> ffmpeg -f avfoundation -capture_raw_data true -i :2 -filter_complex "\
> [0:a]pan=1C|c0=c0[a0];\
> [0:a]pan=1C|c0=c1[a1];\
> [a0][a1]amerge=inputs=2[a3]" -map '[a3]' \
> -f s16le - \
> | ffmpeg -loglevel debug \
> -acodec ac3 -i - \
> -af 'pan=5.1|c0=FL|c1=FR|c4=FC|c5=LFE|c2=SL|c3=SR' \
> -ar 48000 -y output.wav
>
> How can I clean this up and make it more stable?
>
> Thanks
> -Fred
>
> On 28/10/2023 15:36, Fred Rotbart wrote:
>> Here is one of my many other attempts. It should be clear that I am a
>> beginner with ffmpeg.
>>
>> No matter what I try, ffmpeg seems to merge all the 32 USB channels
>> into 6.
>>
>> For example:
>>
>> ffmpeg -ac 2 -c ac3 -loglevel debug -f avfoundation -i :2 -af
>> 'pan=5.1' output.wav
>>
>> Part of the output:
>>
>> Splitting the commandline.
>> Reading option '-ac' ... matched as option 'ac' (set number of audio
>> channels) with argument '2'.
>> Reading option '-c' ... matched as option 'c' (codec name) with
>> argument 'ac3'.
>> Reading option '-loglevel' ... matched as option 'loglevel' (set
>> logging level) with argument 'debug'.
>> Reading option '-f' ... matched as option 'f' (force format) with
>> argument 'avfoundation'.
>> Reading option '-i' ... matched as input url with argument ':2'.
>> Reading option '-af' ... matched as option 'af' (set audio filters)
>> with argument 'pan=5.1'.
>> Reading option 'output.wav' ... matched as output url.
>> Finished splitting the commandline.
>> Parsing a group of options: global .
>> Applying option loglevel (set logging level) with argument debug.
>> Successfully parsed a group of options.
>> Parsing a group of options: input url :2.
>> Applying option ac (set number of audio channels) with argument 2.
>> Applying option c (codec name) with argument ac3.
>> Applying option f (force format) with argument avfoundation.
>> Successfully parsed a group of options.
>> Opening an input file: :2.
>> [avfoundation @ 0x7f96400041c0] audio device 'Digiface USB
>> (24162724)' opened
>> For transform of length 128, inverse, mdct_float, flags: [aligned,
>> out_of_place], found 3 matches:
>> 1: mdct_inv_float_avx2 - type: mdct_float, len: [16, ∞],
>> factors[2]: [2, any], flags: [aligned, out_of_place, inv_only], prio:
>> 544
>> 2: mdct_inv_float_c - type: mdct_float, len: [2, ∞], factors[2]:
>> [2, any], flags: [unaligned, out_of_place, inv_only], prio: 96
>> 3: mdct_naive_inv_float_c - type: mdct_float, len: [2, ∞],
>> factors[2]: [2, any], flags: [unaligned, out_of_place, inv_only],
>> prio: -130976
>> For transform of length 64, inverse, fft_float, flags: [aligned,
>> inplace, preshuf, asm_call], found 3 matches:
>> 1: fft_sr_asm_float_avx2 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 480
>> 2: fft_sr_asm_float_fma3 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 448
>> 3: fft_sr_asm_float_avx - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 416
>> Transform tree:
>> mdct_inv_float_avx2 - type: mdct_float, len: 128, factors[2]: [2,
>> any], flags: [aligned, out_of_place, inv_only]
>> fft_sr_asm_float_avx2 - type: fft_float, len: 64, factor: 2,
>> flags: [aligned, inplace, out_of_place, preshuf, asm_call]
>> For transform of length 256, inverse, mdct_float, flags: [aligned,
>> out_of_place], found 3 matches:
>> 1: mdct_inv_float_avx2 - type: mdct_float, len: [16, ∞],
>> factors[2]: [2, any], flags: [aligned, out_of_place, inv_only], prio:
>> 544
>> 2: mdct_inv_float_c - type: mdct_float, len: [2, ∞], factors[2]:
>> [2, any], flags: [unaligned, out_of_place, inv_only], prio: 96
>> 3: mdct_naive_inv_float_c - type: mdct_float, len: [2, ∞],
>> factors[2]: [2, any], flags: [unaligned, out_of_place, inv_only],
>> prio: -130976
>> For transform of length 128, inverse, fft_float, flags: [aligned,
>> inplace, preshuf, asm_call], found 3 matches:
>> 1: fft_sr_asm_float_avx2 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 480
>> 2: fft_sr_asm_float_fma3 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 448
>> 3: fft_sr_asm_float_avx - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 416
>> Transform tree:
>> mdct_inv_float_avx2 - type: mdct_float, len: 256, factors[2]: [2,
>> any], flags: [aligned, out_of_place, inv_only]
>> fft_sr_asm_float_avx2 - type: fft_float, len: 128, factor: 2,
>> flags: [aligned, inplace, out_of_place, preshuf, asm_call]
>> [avfoundation @ 0x7f96400041c0] All info found
>> Input #0, avfoundation, from ':2':
>> Duration: N/A, start: 1307454.032041, bitrate: N/A
>> Stream #0:0, 1, 1/1000000: Audio: ac3, 44100 Hz, 32 channels, fltp
>> Successfully opened the file.
>> Parsing a group of options: output url output.wav.
>> Applying option af (set audio filters) with argument pan=5.1.
>> Successfully parsed a group of options.
>> Opening an output file: output.wav.
>> File 'output.wav' already exists. Overwrite? [y/N] y
>> [file @ 0x7f9640108000] Setting default whitelist 'file,crypto,data'
>> Successfully opened the file.
>> For transform of length 128, inverse, mdct_float, flags: [aligned,
>> out_of_place], found 3 matches:
>> 1: mdct_inv_float_avx2 - type: mdct_float, len: [16, ∞],
>> factors[2]: [2, any], flags: [aligned, out_of_place, inv_only], prio:
>> 544
>> 2: mdct_inv_float_c - type: mdct_float, len: [2, ∞], factors[2]:
>> [2, any], flags: [unaligned, out_of_place, inv_only], prio: 96
>> 3: mdct_naive_inv_float_c - type: mdct_float, len: [2, ∞],
>> factors[2]: [2, any], flags: [unaligned, out_of_place, inv_only],
>> prio: -130976
>> For transform of length 64, inverse, fft_float, flags: [aligned,
>> inplace, preshuf, asm_call], found 3 matches:
>> 1: fft_sr_asm_float_avx2 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 480
>> 2: fft_sr_asm_float_fma3 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 448
>> 3: fft_sr_asm_float_avx - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 416
>> Transform tree:
>> mdct_inv_float_avx2 - type: mdct_float, len: 128, factors[2]: [2,
>> any], flags: [aligned, out_of_place, inv_only]
>> fft_sr_asm_float_avx2 - type: fft_float, len: 64, factor: 2,
>> flags: [aligned, inplace, out_of_place, preshuf, asm_call]
>> For transform of length 256, inverse, mdct_float, flags: [aligned,
>> out_of_place], found 3 matches:
>> 1: mdct_inv_float_avx2 - type: mdct_float, len: [16, ∞],
>> factors[2]: [2, any], flags: [aligned, out_of_place, inv_only], prio:
>> 544
>> 2: mdct_inv_float_c - type: mdct_float, len: [2, ∞], factors[2]:
>> [2, any], flags: [unaligned, out_of_place, inv_only], prio: 96
>> 3: mdct_naive_inv_float_c - type: mdct_float, len: [2, ∞],
>> factors[2]: [2, any], flags: [unaligned, out_of_place, inv_only],
>> prio: -130976
>> For transform of length 128, inverse, fft_float, flags: [aligned,
>> inplace, preshuf, asm_call], found 3 matches:
>> 1: fft_sr_asm_float_avx2 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 480
>> 2: fft_sr_asm_float_fma3 - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 448
>> 3: fft_sr_asm_float_avx - type: fft_float, len: [64, 131072],
>> factor: 2, flags: [aligned, inplace, out_of_place, preshuf,
>> asm_call], prio: 416
>> Transform tree:
>> mdct_inv_float_avx2 - type: mdct_float, len: 256, factors[2]: [2,
>> any], flags: [aligned, out_of_place, inv_only]
>> fft_sr_asm_float_avx2 - type: fft_float, len: 128, factor: 2,
>> flags: [aligned, inplace, out_of_place, preshuf, asm_call]
>> Stream mapping:
>> Stream #0:0 -> #0:0 (ac3 (native) -> pcm_s16le (native))
>> Press [q] to stop, [?] for help
>> [aost#0:0/pcm_s16le @ 0x7f963f745840] cur_dts is invalid [init:0
>> i_done:0 finish:0] (this is harmless if it occurs once at the start
>> per stream)
>> [AVFilterGraph @ 0x7fe03c4115c0] Setting 'args' to value '5.1'
>> detected 12 logical cores
>> [graph_0_in_0_0 @ 0x7fe03c4081c0] Setting 'time_base' to value '1/48000'
>> [graph_0_in_0_0 @ 0x7fe03c4081c0] Setting 'sample_rate' to value '48000'
>> [graph_0_in_0_0 @ 0x7fe03c4081c0] Setting 'sample_fmt' to value 'fltp'
>> [graph_0_in_0_0 @ 0x7fe03c4081c0] Setting 'channels' to value '32'
>> [graph_0_in_0_0 @ 0x7fe03c4081c0] tb:1/48000 samplefmt:fltp
>> samplerate:48000 chlayout:32 channels
>> [format_out_0_0 @ 0x7fe03c404200] Setting 'sample_fmts' to value 's16'
>> [format_out_0_0 @ 0x7fe03c404200] auto-inserting filter
>> 'auto_aresample_0' between the filter 'Parsed_pan_0' and the filter
>> 'format_out_0_0'
>> [AVFilterGraph @ 0x7fe03c4115c0] query_formats: 4 queried, 6 merged,
>> 3 already done, 0 delayed
>> [Parsed_pan_0 @ 0x7fe03c40e180] [SWR @ 0x7fe040b00000] Using fltp
>> internally between filters
>> [Parsed_pan_0 @ 0x7fe03c40e180] o0 = 0 i0 + 0 i1 + 0 i2 + 0 i3 + 0 i4
>> + 0 i5 + 0 i6 + 0 i7 + 0 i8 + 0 i9 + 0 i10 + 0 i11 + 0 i12 + 0 i13 +
>> 0 i14 + 0 i15 + 0 i16 + 0 i17 + 0 i18 + 0 i19 + 0 i20 + 0 i21 + 0 i22
>> + 0 i23 + 0 i24 + 0 i25 + 0 i26 + 0 i27 + 0 i28 + 0 i29 + 0 i30 + 0 i31
>> [Parsed_pan_0 @ 0x7fe03c40e180] o1 = 0 i0 + 0 i1 + 0 i2 + 0 i3 + 0 i4
>> + 0 i5 + 0 i6 + 0 i7 + 0 i8 + 0 i9 + 0 i10 + 0 i11 + 0 i12 + 0 i13 +
>> 0 i14 + 0 i15 + 0 i16 + 0 i17 + 0 i18 + 0 i19 + 0 i20 + 0 i21 + 0 i22
>> + 0 i23 + 0 i24 + 0 i25 + 0 i26 + 0 i27 + 0 i28 + 0 i29 + 0 i30 + 0 i31
>> [Parsed_pan_0 @ 0x7fe03c40e180] o2 = 0 i0 + 0 i1 + 0 i2 + 0 i3 + 0 i4
>> + 0 i5 + 0 i6 + 0 i7 + 0 i8 + 0 i9 + 0 i10 + 0 i11 + 0 i12 + 0 i13 +
>> 0 i14 + 0 i15 + 0 i16 + 0 i17 + 0 i18 + 0 i19 + 0 i20 + 0 i21 + 0 i22
>> + 0 i23 + 0 i24 + 0 i25 + 0 i26 + 0 i27 + 0 i28 + 0 i29 + 0 i30 + 0 i31
>> [Parsed_pan_0 @ 0x7fe03c40e180] o3 = 0 i0 + 0 i1 + 0 i2 + 0 i3 + 0 i4
>> + 0 i5 + 0 i6 + 0 i7 + 0 i8 + 0 i9 + 0 i10 + 0 i11 + 0 i12 + 0 i13 +
>> 0 i14 + 0 i15 + 0 i16 + 0 i17 + 0 i18 + 0 i19 + 0 i20 + 0 i21 + 0 i22
>> + 0 i23 + 0 i24 + 0 i25 + 0 i26 + 0 i27 + 0 i28 + 0 i29 + 0 i30 + 0 i31
>> [Parsed_pan_0 @ 0x7fe03c40e180] o4 = 0 i0 + 0 i1 + 0 i2 + 0 i3 + 0 i4
>> + 0 i5 + 0 i6 + 0 i7 + 0 i8 + 0 i9 + 0 i10 + 0 i11 + 0 i12 + 0 i13 +
>> 0 i14 + 0 i15 + 0 i16 + 0 i17 + 0 i18 + 0 i19 + 0 i20 + 0 i21 + 0 i22
>> + 0 i23 + 0 i24 + 0 i25 + 0 i26 + 0 i27 + 0 i28 + 0 i29 + 0 i30 + 0 i31
>> [Parsed_pan_0 @ 0x7fe03c40e180] o5 = 0 i0 + 0 i1 + 0 i2 + 0 i3 + 0 i4
>> + 0 i5 + 0 i6 + 0 i7 + 0 i8 + 0 i9 + 0 i10 + 0 i11 + 0 i12 + 0 i13 +
>> 0 i14 + 0 i15 + 0 i16 + 0 i17 + 0 i18 + 0 i19 + 0 i20 + 0 i21 + 0 i22
>> + 0 i23 + 0 i24 + 0 i25 + 0 i26 + 0 i27 + 0 i28 + 0 i29 + 0 i30 + 0 i31
>> [Parsed_pan_0 @ 0x7fe03c40e180] Pure channel mapping detected: M M M
>> M M M
>> [auto_aresample_0 @ 0x7fe03c40d280] [SWR @ 0x7fe03c72d000] Using fltp
>> internally between filters
>> [auto_aresample_0 @ 0x7fe03c40d280] ch:6 chl:5.1 fmt:fltp r:44100Hz
>> -> ch:6 chl:5.1 fmt:s16 r:48000Hz
>> Output #0, wav, to 'output.wav':
>> Metadata:
>> ISFT : Lavf60.3.100
>> Stream #0:0, 0, 1/48000: Audio: pcm_s16le ([1][0][0][0] /
>> 0x0001), 48000 Hz, 5.1, s16, 4233 kb/s
>> Metadata:
>> encoder : Lavc60.3.100 pcm_s16le
>> [out#0/wav @ 0x7fe03b704840] All streams finished
>> [out#0/wav @ 0x7fe03b704840] Terminating muxer thread
>>
>> I've read all the documentation and searched all the forums but could
>> not find anything that would give me a clue.
>> Please help.
>>
>> - Fred
>>
>> On 25/10/2023 14:00, Fred Rotbart wrote:
>>> Hi,
>>>
>>> I have a RME Digiface USB as input to my Mac. This has 32 SPDIF
>>> input channels, of which the first two have an ac3 signal and the
>>> others are not used.
>>> I have been trying to isolate and decode one of the ac3 channels to
>>> its six separate PCM channels but without success.
>>>
>>> For example, as one of the many attempts, I tried:
>>>
>>> ffmpeg -acodec ac3 -f avfoundation -capture_raw_data true -i :1 \
>>> -map_channel 0.0.0, \
>>> -af 'pan=5.1|c0=c0|c1=-|c2=FC|c3=LFE|c4=BL|c5=BR' \
>>> output.wav
>>>
>>> Can someone help me with this?
>>>
>>> - Fred
>>>
More information about the ffmpeg-user
mailing list