Alsa cannot set sample format[FFMPEG]

问题

I am trying to capture a pcm stream from a Roland USB device with ffmpeg and wrap it with wav. The command line I am using is the following:

ffmpeg -f alsa -acodec pcm_s32le -ac 2 -ar 48000 -i hw:2,0 out.wav

Which comply with the settings of the hardware. I can also capture the stream with Audacity. The problem is that FFMPEG throws "cannot set sample format error". Any idea of what may be happening and how I can fix this?

Thanks in advance.

FFMPEG OUTPUT

user@user:~$ ffmpeg -f alsa -acodec pcm_s32le -ac 2 -ar 48000 -i hw:2,0 out.wav
    ffmpeg version N-85548-g3390a2b Copyright (c) 2000-2017 the FFmpeg developers
      built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
      configuration: --enable-gpl --enable-libx264 --enable-libx265 --enable-libvpx --enable-libvorbis --enable-libopus --enable-ffplay
      libavutil      55. 61.100 / 55. 61.100
      libavcodec     57. 92.100 / 57. 92.100
      libavformat    57. 72.101 / 57. 72.101
      libavdevice    57.  7.100 / 57.  7.100
      libavfilter     6. 84.101 /  6. 84.101
      libswscale      4.  7.101 /  4.  7.101
      libswresample   2.  8.100 /  2.  8.100
      libpostproc    54.  6.100 / 54.  6.100
    [alsa @ 0x34b6780] cannot set sample format 0x10008 10 (Invalid argument)
    hw:2,0: Input/output error

ARECORD OUTPUT:

user@user:~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: PCH [HDA Intel PCH], device 0: ALC3236 Analog [ALC3236 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: DUOCAPTURE [DUO-CAPTURE], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

After Deimus help I checked the setting for my card in arecord and used the correct line for FFMPEG (Notice that I have changed the capture frequency on the hardware).

ARECORD OUTPUT

user@user:~$ arecord --dump-hw-params -D hw:2,0
Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
HW Params of device "hw:2,0":
--------------------
ACCESS:  MMAP_INTERLEAVED RW_INTERLEAVED
FORMAT:  S24_3LE
SUBFORMAT:  STD
SAMPLE_BITS: 24
FRAME_BITS: 48
CHANNELS: 2
RATE: 44100
PERIOD_TIME: (1020 1981429)
PERIOD_SIZE: [45 87381]
PERIOD_BYTES: [270 524286]
PERIODS: [2 1024]
BUFFER_TIME: (2040 3962858)
BUFFER_SIZE: [90 174762]
BUFFER_BYTES: [540 1048572]
TICK_TIME: ALL
--------------------
arecord: set_params:1233: Sample format non available
Available formats:
- S24_3LE

Correct command line

ffmpeg -f alsa -acodec pcm_s24le -ac 2 -ar 44100 -i hw:2,0 out.wav

回答1:

Use the --dump-hw-params option of arecord tool to check the supported sample formats.

Man page for arecord

Then you can use the -sample_fmt option of ffmpeg to specficy the format eg. s32

Audio options for ffmpeg are here

回答2:

Refer to output of arecord --dump-hw-params -D hw:2,0 where hw:2,0 is your target device.

arecord output will show available sample formats under FORMAT and Available formats. Other useful info is also shown such as CHANNELS and RATE. Example:

--------------------
ACCESS:  MMAP_INTERLEAVED RW_INTERLEAVED
FORMAT:  S16_LE S32_LE
SUBFORMAT:  STD
SAMPLE_BITS: [16 32]
FRAME_BITS: [32 64]
CHANNELS: 2
RATE: [44100 192000]
PERIOD_TIME: (83 11888617)
PERIOD_SIZE: [16 524288]
PERIOD_BYTES: [128 4194304]
PERIODS: [2 32]
BUFFER_TIME: (166 23777234)
BUFFER_SIZE: [32 1048576]
BUFFER_BYTES: [128 4194304]
TICK_TIME: ALL
--------------------
Available formats:
- S16_LE
- S32_LE

In your ffmpeg command choose the appropriate decoder to match the sample format. You can also choose the channels and sample rate:
```
ffmpeg -f alsa -c:a pcm_s32le -channels 2 -sample_rate 44100 -i hw:2,0 output.wav
```

Examples of decoders to use:

S16LE = -c:a pcm_s16le
S24LE = -c:a pcm_s24le
S32LE = -c:a pcm_s32le

Also see ffmpeg -decoders and FFmpeg Documentation: ALSA input.

来源：https://stackoverflow.com/questions/44049854/alsa-cannot-set-sample-formatffmpeg

标签

Linux

ffmpeg

command-line-interface

alsa