Screenrecording, audio is sped up when other process starts

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Screenrecording, audio is sped up when other process starts

Tarjei Bærland
Hello!

I have an issue where my audio is sped up when I start certain process
while running ffmpeg. You can hear it after about 13 seconds in this video:
https://www.youtube.com/watch?v=aGr2pDgZ_6k (it's in Norwegian and
informal, as it is meant for fourteen highschool students), where it
happens when I start a python process where pygame is loaded.


Does anyone have any idea what could be the cause, and what I could do to
remedy it?

I have startet ffmpeg by the following command

 ffmpeg \
    -f x11grab \
    -video_size 1920x1080 \
    -i $DISPLAY.0+1920,0 \
    -f alsa \
    -acodec pcm_s32le \
    -ac 4 \
    -ar 44100 \
    -i  sysdefault:CARD=U192k \
    -filter:a "volume=10dB" \
    -preset ultrafast \
    -c:v libx264 \
    -y \
    -ac 1 \
    -threads 4 \
    ${OUTFILE}


My audiocard is a Behringer UMC404HD.

All help is very much appreciated.

Kind regards,
Tarjei Bærland
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Re: Screenrecording, audio is sped up when other process starts

DEF-2
On Tue, 24 Mar 2020 at 21:04 Tarjei Bærland <[hidden email]>
wrote:

> Hello!
>
> I have an issue where my audio is sped up when I start certain process
> while running ffmpeg. You can hear it after about 13 seconds in this video:
> https://www.youtube.com/watch?v=aGr2pDgZ_6k (it's in Norwegian and
> informal, as it is meant for fourteen highschool students), where it
> happens when I start a python process where pygame is loaded.
>
>
> Does anyone have any idea what could be the cause, and what I could do to
> remedy it?
>
> I have startet ffmpeg by the following command
>
>  ffmpeg \
>     -f x11grab \
>     -video_size 1920x1080 \
>     -i $DISPLAY.0+1920,0 \
>     -f alsa \
>     -acodec pcm_s32le \
>     -ac 4 \
>     -ar 44100 \
>     -i  sysdefault:CARD=U192k \
>     -filter:a "volume=10dB" \
>     -preset ultrafast \
>     -c:v libx264 \
>     -y \
>     -ac 1 \
>     -threads 4 \
>     ${OUTFILE}


Console output  up till when you start the python process please.


>
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Re: Screenrecording, audio is sped up when other process starts

kumowoon1025
In reply to this post by Tarjei Bærland
Hi,

If you only need mic audio, grab hardware device exclusively or make sure pygame doesn’t touch the same card/device.

Regards,
Ted Park

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Re: Screenrecording, audio is sped up when other process starts

Tarjei Bærland
In reply to this post by DEF-2
I start the same python program as in the youtube movie after about 10
seconds here. To the same effect.

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--enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack
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--enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab
--enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264
--enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid
--enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
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  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
[x11grab @ 0x55a8e7b02280] Stream #0: not enough frames to estimate rate;
consider increasing probesize
Input #0, x11grab, from ':0.0+1920,0':
  Duration: N/A, start: 1585082286.995363, bitrate: N/A
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080,
29.97 fps, 1000k tbr, 1000k tbn, 1000k tbc
Guessed Channel Layout for Input Stream #1.0 : 4.0
Input #1, alsa, from 'sysdefault:CARD=U192k':
  Duration: N/A, start: 1585082286.815026, bitrate: 5644 kb/s
    Stream #1:0: Audio: pcm_s32le, 44100 Hz, 4.0, s32, 5644 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
  Stream #1:0 -> #0:1 (pcm_s32le (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x55a8e7b75a80] using cpu capabilities: MMX2 SSE2Fast SSSE3
SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x55a8e7b75a80] profile High 4:4:4 Predictive, level 4.0, 4:4:4,
8-bit
[libx264 @ 0x55a8e7b75a80] 264 - core 159 r2991 1771b55 - H.264/MPEG-4 AVC
codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html - options:
cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1
psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0
cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=6 threads=4
lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0
bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250
keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=23.0
qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
Output #0, mp4, to '/tmp/out.mp4':
  Metadata:
    encoder         : Lavf58.29.100
    Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661),
yuv444p(progressive), 1920x1080, q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
    Metadata:
      encoder         : Lavc58.54.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp,
69 kb/s
    Metadata:
      encoder         : Lavc58.54.100 aac
[x11grab @ 0x55a8e7b02280] Thread message queue blocking; consider raising
the thread_queue_size option (current value: 8)
frame=   19 fps=0.0 q=13.0 size=     256kB time=00:00:00.47
bitrate=4383.5kbits/s dup=15 drop=1 speed=0.952x
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480.7kbits/s dup=113 drop=9 speed=0.997x
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377.1kbits/s dup=139 drop=9 speed=   1x
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490.1kbits/s dup=142 drop=9 speed=0.997x
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476.0kbits/s dup=146 drop=9 speed=0.997x
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462.1kbits/s dup=150 drop=9 speed=0.998x
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449.6kbits/s dup=154 drop=9 speed=0.998x
frame=  578 fps= 30 q=-1.0 Lsize=    1207kB time=00:00:19.25 bitrate=
513.6kbits/s dup=157 drop=9 speed=1.01x
video:1028kB audio:157kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 1.868276%
[libx264 @ 0x55a8e7b75a80] frame I:3     Avg QP:13.67  size:182376
[libx264 @ 0x55a8e7b75a80] frame P:575   Avg QP:13.29  size:   879
[libx264 @ 0x55a8e7b75a80] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0x55a8e7b75a80] mb P  I16..4:  0.4%  0.0%  0.0%  P16..4:  0.3%
 0.0%  0.0%  0.0%  0.0%    skip:99.3%
[libx264 @ 0x55a8e7b75a80] coded y,u,v intra: 8.5% 5.6% 5.5% inter: 0.1%
0.1% 0.1%
[libx264 @ 0x55a8e7b75a80] i16 v,h,dc,p: 86% 13%  1%  0%
[libx264 @ 0x55a8e7b75a80] kb/s:436.50
[aac @ 0x55a8e7b77200] Qavg: 119.592
Exiting normally, received signal 15.

tir. 24. mar. 2020 kl. 21:25 skrev DEF <[hidden email]>:

> On Tue, 24 Mar 2020 at 21:04 Tarjei Bærland <[hidden email]>
> wrote:
>
> > Hello!
> >
> > I have an issue where my audio is sped up when I start certain process
> > while running ffmpeg. You can hear it after about 13 seconds in this
> video:
> > https://www.youtube.com/watch?v=aGr2pDgZ_6k (it's in Norwegian and
> > informal, as it is meant for fourteen highschool students), where it
> > happens when I start a python process where pygame is loaded.
> >
> >
> > Does anyone have any idea what could be the cause, and what I could do to
> > remedy it?
> >
> > I have startet ffmpeg by the following command
> >
> >  ffmpeg \
> >     -f x11grab \
> >     -video_size 1920x1080 \
> >     -i $DISPLAY.0+1920,0 \
> >     -f alsa \
> >     -acodec pcm_s32le \
> >     -ac 4 \
> >     -ar 44100 \
> >     -i  sysdefault:CARD=U192k \
> >     -filter:a "volume=10dB" \
> >     -preset ultrafast \
> >     -c:v libx264 \
> >     -y \
> >     -ac 1 \
> >     -threads 4 \
> >     ${OUTFILE}
>
>
> Console output  up till when you start the python process please.
>
>
> >
> _______________________________________________
> ffmpeg-user mailing list
> [hidden email]
> https://ffmpeg.org/mailman/listinfo/ffmpeg-user
>
> To unsubscribe, visit link above, or email
> [hidden email] with subject "unsubscribe".

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Re: Screenrecording, audio is sped up when other process starts

Tarjei Bærland
In reply to this post by kumowoon1025
tir. 24. mar. 2020 kl. 21:40 skrev Ted Park <[hidden email]>:

> Hi,
>
> If you only need mic audio, grab hardware device exclusively or make sure
> pygame doesn’t touch the same card/device.
>
> Regards,
> Ted Park
>
>

With the risk of sounding ignorant ... how would I "grab hardware device
exclusively"?

I can't with my limiting googling capabilities find out how to not enable
the sound mixer in pygame.

However, the "glitch" persists even after completely closing the python
process.

Regards,
Tarjei
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Re: Screenrecording, audio is sped up when other process starts

Tarjei Bærland
Hi again!

I "disabled" audio from Pygame by

import os
os.putenv('SDL_AUDIODRIVER', 'dummy')
os.putenv('SDL_AUDIODEV', '/dev/null')

which worked. Thanks for help!

How, however, could I ensure something like this not happening when I
launch another program who would like access to my default sound driver?

Regards,
Tarjei

tir. 24. mar. 2020 kl. 21:49 skrev Tarjei Bærland <[hidden email]
>:

>
> tir. 24. mar. 2020 kl. 21:40 skrev Ted Park <[hidden email]>:
>
>> Hi,
>>
>> If you only need mic audio, grab hardware device exclusively or make sure
>> pygame doesn’t touch the same card/device.
>>
>> Regards,
>> Ted Park
>>
>>
>
> With the risk of sounding ignorant ... how would I "grab hardware device
> exclusively"?
>
> I can't with my limiting googling capabilities find out how to not enable
> the sound mixer in pygame.
>
> However, the "glitch" persists even after completely closing the python
> process.
>
> Regards,
> Tarjei
>
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Re: Screenrecording, audio is sped up when other process starts

kumowoon1025
In reply to this post by Tarjei Bærland
Hi,

> With the risk of sounding ignorant ... how would I "grab hardware device
> exclusively"?

To use an account part of the audio group and specifying an actual hardware device should be enough to do this. I am not sure what the difference between cards and devices are to alsa tbh, but I think using hw and index to specify the device makes it clear its not a mixer or other.

Also, does the card have 4 separate streams? If you have no particular reason to get all 4 channels maybe there is a way to only record one.

> I can't with my limiting googling capabilities find out how to not enable
> the sound mixer in pygame.
>
> However, the "glitch" persists even after completely closing the python
> process.

But maybe I was wrong in assuming that the contention in controlling the device was the problem; iirc, the way to not enable the sound mixer in pygame is to not enable it… So if there’s no sound I don’t think that is the issue.

I thought the glitch was the short high pitched noise in the video at 13 seconds in, is it observable anywhere else in that clip?

Regards,
Ted Park

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Re: Screenrecording, audio is sped up when other process starts

Tarjei Bærland
>
> > With the risk of sounding ignorant ... how would I "grab hardware device
> > exclusively"?
>
> To use an account part of the audio group and specifying an actual
> hardware device should be enough to do this. I am not sure what the
> difference between cards and devices are to alsa tbh, but I think using hw
> and index to specify the device makes it clear its not a mixer or other.
>
> Also, does the card have 4 separate streams? If you have no particular
> reason to get all 4 channels maybe there is a way to only record one.
>

It's an external sound card with 4 separate inputs, yes. The reason for my
not specifying hardware numbers is that those tend to reset when I unplug
the card.


> > I can't with my limiting googling capabilities find out how to not enable
> > the sound mixer in pygame.
> >
> > However, the "glitch" persists even after completely closing the python
> > process.
>
> But maybe I was wrong in assuming that the contention in controlling the
> device was the problem; iirc, the way to not enable the sound mixer in
> pygame is to not enable it… So if there’s no sound I don’t think that is
> the issue.
>
>
It seems Pygame runs a check or something at pygame.init. But setting
"dummy" for the environment variable SDL_AUDIODRIVER did the trick.


> I thought the glitch was the short high pitched noise in the video at 13
> seconds in, is it observable anywhere else in that clip?
>

There's that, and the raise in pitch in my voice throughout the rest of the
clip.

Either way, I have something that works now, so many thanks!

 Regards,
Tarjei
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Re: Screenrecording, audio is sped up when other process starts

Carl Eugen Hoyos-2
In reply to this post by Tarjei Bærland
Am Di., 24. März 2020 um 21:50 Uhr schrieb Tarjei Bærland
<[hidden email]>:

> frame=  578 fps= 30 q=-1.0 Lsize=    1207kB time=00:00:19.25 bitrate=
> 513.6kbits/s dup=157 drop=9 speed=1.01x

mkv output may avoid the duplicated frames and lead to smaller files.
(FFmpeg's mov / mp4 muxer does not support variable frame rate,
your screen seems to send frames less often than advertised.)

Please remember not to top-post here.

Carl Eugen
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Re: Screenrecording, audio is sped up when other process starts

kumowoon1025
In reply to this post by Tarjei Bærland
Hi,

> I "disabled" audio from Pygame by
>
> import os
> os.putenv('SDL_AUDIODRIVER', 'dummy')
> os.putenv('SDL_AUDIODEV', '/dev/null')
>
> which worked. Thanks for help!

Oh.. I guess I was wrong, I feel like there must be a way to configure the sound from within pygame instead of setting an environment variable...


> How, however, could I ensure something like this not happening when I
> launch another program who would like access to my default sound driver?

Yeah, I suppose more likely than not you will want to record sound coming from the game also.


>> Also, does the card have 4 separate streams? If you have no particular
>> reason to get all 4 channels maybe there is a way to only record one.
> It's an external sound card with 4 separate inputs, yes. The reason for my
> not specifying hardware numbers is that those tend to reset when I unplug
> the card.

That’s understandable for removable interface.

I did see that your sound card outputs 4 channels what about the stream count? I think they present as subdevices if they are actual discrete streams, but not if they are coupled channels.

> There's that, and the raise in pitch in my voice throughout the rest of the
> clip.
>
> Either way, I have something that works now, so many thanks!

I… your welcome but if you bought a dedicated multichannel audio card or interface you should be able to route multiple sources when/if you need in the future…

If you made sure to use the same settings (sample rate, format, different streams/subdevices) you could actually get exclusive control and share the hardware device. I could be wrong but a 4 ch card is probably going to have at least two streams available, maybe separate clocks, usually not, or even 4 discrete.

You could not use a hardware device at all, and use alsa’s software converted/mixed/resampled software plugins/devices sharing input/output will be much easier. I believe you can also set a system default mixer or plugin, unfortunately the only thing I remember was that I couldn't not figure out how to set up alsa the way I wanted it and gave up halfway through :/

But see if $ aplay -L lists software device systemdefaults that seem adequate for you, then you could try if using those names instead give satisfactory results, since the audio format resampling will be handled for you by alsa even if clients use different configurations.

Regards,
Ted Park

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