[FFmpeg-trac] #6156(undetermined:new): Issue with FFMPEG ALSA CPU usage
FFmpeg
trac at avcodec.org
Sat Feb 18 04:32:40 EET 2017
#6156: Issue with FFMPEG ALSA CPU usage
-------------------------------------+-------------------------------------
Reporter: mushm0m | Owner:
Type: defect | Status: new
Priority: normal | Component:
Version: git-master | undetermined
Keywords: alsa | Resolution:
Blocking: | Blocked By:
Analyzed by developer: 0 | Reproduced by developer: 0
-------------------------------------+-------------------------------------
Changes (by llogan):
* keywords: ALSA => alsa
* version: unspecified => git-master
* component: avcodec => undetermined
Old description:
> I am on a Raspberry Pi Zero with a Pi Camera and an I2S MEMS mic, running
> the latest Raspbian Jessie. I am attempting to livestream audio and
> video. I've discovered that when I record ALSA audio with FFMPEG, that
> process takes 95% of my CPU and produces stuttering, unusable audio in
> the stream.
>
> I have compiled FFMPEG with ALSA following this: http://vpaste.net/cXV9F
>
> I isolated the issue to the following:
>
> 1. ffmpeg -f alsa -acodec pcm_s32le -i mic_sv temp.wav
> This single command takes 95% of my CPU.
>
> 2. arecord -Dmic_sv -c2 -r48000 -fS32_LE -twav temp.wav
> This single command takes <5% of my CPU.
>
> I have added a custom hook to ffmpeg so we can see the PCM settings. I
> have ensured that settings (buffer size, period size, etc.) are identical
> between the two commands.
>
> Here is the full console output of FFMPEG: http://vpaste.net/2M5gk
> Here is the console output of Arecord: http://vpaste.net/CPk3A
>
> After a long chat in the FFMPEG IRC channel, we believe there may be a
> bug in the way FFMPEG waits for ALSA packets. Arecord uses snd_pcm_wait()
> to wait for packets, and this command is not used in FFMPEG sources.
> Inserting '-re' before -i into my FFMPEG command reduces CPU usage to
> <5%, but is not the right approach, and causes other problems (bitrate is
> almost 0kbps, audio file generated is <5 kilobytes).
New description:
I am on a Raspberry Pi Zero with a Pi Camera and an I2S MEMS mic, running
the latest Raspbian Jessie. I am attempting to livestream audio and video.
I've discovered that when I record ALSA audio with FFMPEG, that process
takes 95% of my CPU and produces stuttering, unusable audio in the stream.
I isolated the issue to the following:
1. `ffmpeg -f alsa -acodec pcm_s32le -i mic_sv temp.wav`
This single command takes 95% of my CPU.
2. `arecord -Dmic_sv -c2 -r48000 -fS32_LE -twav temp.wav`
This single command takes <5% of my CPU.
I have added a custom hook to ffmpeg so we can see the PCM settings. I
have ensured that settings (buffer size, period size, etc.) are identical
between the two commands.
Here is the full console output of FFMPEG:
{{{
$ ALSA_CONFIG_PATH=/usr/share/alsa/alsa.conf:./dumpasoundrc
/home/pi/special/ffmpeg/ffmpeg -v 9 -loglevel 99 -f alsa -acodec
pcm_s32le -i michooks -f null -
ffmpeg version git-2017-02-05-e57fd92 Copyright (c) 2000-2017 the FFmpeg
developers
built with gcc 4.9.2 (Raspbian 4.9.2-10)
configuration: --extra-cflags=-I/opt/vc/include/IL --enable-nonfree
--enable-omx-rpi --logfile=CONFIG.TXT
libavutil 55. 46.100 / 55. 46.100
libavcodec 57. 75.100 / 57. 75.100
libavformat 57. 66.101 / 57. 66.101
libavdevice 57. 2.100 / 57. 2.100
libavfilter 6. 73.100 / 6. 73.100
libswscale 4. 3.101 / 4. 3.101
libswresample 2. 4.100 / 2. 4.100
Splitting the commandline.
Reading option '-v' ... matched as option 'v' (set logging level) with
argument '9'.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging
level) with argument '99'.
Reading option '-f' ... matched as option 'f' (force format) with argument
'alsa'.
Reading option '-acodec' ... matched as option 'acodec' (force audio codec
('copy' to copy stream)) with argument 'pcm_s32le'.
Reading option '-i' ... matched as input url with argument 'michooks'.
Reading option '-f' ... matched as option 'f' (force format) with argument
'null'.
Reading option '-' ... matched as output url.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option v (set logging level) with argument 9.
Successfully parsed a group of options.
Parsing a group of options: input url michooks.
Applying option f (force format) with argument alsa.
Applying option acodec (force audio codec ('copy' to copy stream)) with
argument pcm_s32le.
Successfully parsed a group of options.
Opening an input file: michooks.
[ALSA Debug Hook] Installing hooks.
Hooks PCM
Slave: Soft volume PCM
Control: Boost Capture Volume
min_dB: -3
max_dB: 50
resolution: 256
Slave: Route conversion PCM
Transformation table:
0 <- 0
1 <- 0
Slave: Mmap emulation PCM
Slave: Hardware PCM card 1 'mems-mic' device 0 subdevice 0
[ALSA Debug Hook] hw_params:
Hooks PCM
Slave: Soft volume PCM
Control: Boost Capture Volume
min_dB: -3
max_dB: 50
resolution: 256
Its setup is:
stream : CAPTURE
access : RW_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Route conversion PCM
Transformation table:
0 <- 0
1 <- 0
Its setup is:
stream : CAPTURE
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Mmap emulation PCM
Its setup is:
stream : CAPTURE
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Hardware PCM card 1 'mems-mic' device 0 subdevice 0
Its setup is:
stream : CAPTURE
access : RW_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1073741824
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
appl_ptr : 0
hw_ptr : 0
[alsa @ 0x31ea450] All info found
[alsa @ 0x31ea450] stream 0: start_time: 1487382765.290 duration:
-9223372036854.775
[alsa @ 0x31ea450] format: start_time: 1487382765.290 duration:
-9223372036854.775 bitrate=3072 kb/s
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'michooks':
Duration: N/A, start: 1487382765.289814, bitrate: 3072 kb/s
Stream #0:0, 1, 1/1000000: Audio: pcm_s32le, 48000 Hz, stereo, s32,
3072 kb/s
Successfully opened the file.
Parsing a group of options: output url -.
Applying option f (force format) with argument null.
Successfully parsed a group of options.
Opening an output file: -.
Successfully opened the file.
detected 1 logical cores
[graph_0_in_0_0 @ 0x31f9310] Setting 'time_base' to value '1/48000'
[graph_0_in_0_0 @ 0x31f9310] Setting 'sample_rate' to value '48000'
[graph_0_in_0_0 @ 0x31f9310] Setting 'sample_fmt' to value 's32'
[graph_0_in_0_0 @ 0x31f9310] Setting 'channel_layout' to value '0x3'
[graph_0_in_0_0 @ 0x31f9310] tb:1/48000 samplefmt:s32 samplerate:48000
chlayout:0x3
[format_out_0_0 @ 0x31f9f10] Setting 'sample_fmts' to value 's16'
[format_out_0_0 @ 0x31f9f10] auto-inserting filter 'auto_resampler_0'
between the filter 'Parsed_anull_0' and the filter 'format_out_0_0'
[AVFilterGraph @ 0x31f9980] query_formats: 4 queried, 6 merged, 3 already
done, 0 delayed
[auto_resampler_0 @ 0x31faf10] [SWR @ 0x321e130] Using fltp internally
between filters
[auto_resampler_0 @ 0x31faf10] ch:2 chl:stereo fmt:s32 r:48000Hz -> ch:2
chl:stereo fmt:s16 r:48000Hz
Output #0, null, to 'pipe:':
Metadata:
encoder : Lavf57.66.101
Stream #0:0, 0, 1/48000: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536
kb/s
Metadata:
encoder : Lavc57.75.100 pcm_s16le
Stream mapping:
Stream #0:0 -> #0:0 (pcm_s32le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
cur_dts is invalid (this is harmless if it occurs once at the start per
stream)
size=N/A time=00:00:17.84 bitrate=N/A speed= 1x
video:0kB audio:3345kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknown
Input file #0 (michooks):
Input stream #0:0 (audio): 26372 packets read (6851424 bytes); 26372
frames decoded (856428 samples);
Total: 26372 packets (6851424 bytes) demuxed
Output file #0 (pipe:):
Output stream #0:0 (audio): 26372 frames encoded (856428 samples); 26372
packets muxed (3425712 bytes);
Total: 26372 packets (3425712 bytes) muxed
26372 frames successfully decoded, 0 decoding errors
Exiting normally, received signal 2.
}}}
Here is the console output of Arecord:
{{{
$ arecord -v -r48000 -c2 -fS32_LE --period-size=16384 --buffer-size=65536
-Dmic_sv -twav /dev/null
Recording WAVE '/dev/null' : Signed 32 bit Little Endian, Rate 48000 Hz,
Stereo
Soft volume PCM
Control: Boost Capture Volume
min_dB: -3
max_dB: 50
resolution: 256
Its setup is:
stream : CAPTURE
access : RW_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Route conversion PCM
Transformation table:
0 <- 0
1 <- 0
Its setup is:
stream : CAPTURE
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Mmap emulation PCM
Its setup is:
stream : CAPTURE
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Hardware PCM card 1 'mems-mic' device 0 subdevice 0
Its setup is:
stream : CAPTURE
access : RW_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 65536
period_size : 16384
period_time : 341333
tstamp_mode : NONE
period_step : 1
avail_min : 16384
period_event : 0
start_threshold : 1073741824
stop_threshold : 65536
silence_threshold: 0
silence_size : 0
boundary : 1073741824
appl_ptr : 0
hw_ptr : 0
^CAborted by signal Interrupt...
}}}
After a long chat in the FFMPEG IRC channel, we believe there may be a bug
in the way FFMPEG waits for ALSA packets. Arecord uses `snd_pcm_wait()` to
wait for packets, and this command is not used in FFMPEG sources.
Inserting `-re` before `-i` into my FFMPEG command reduces CPU usage to
<5%, but is not the right approach, and causes other problems (bitrate is
almost 0kbps, audio file generated is <5 kilobytes).
--
--
Ticket URL: <https://trac.ffmpeg.org/ticket/6156#comment:2>
FFmpeg <https://ffmpeg.org>
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