ffmpeg desktop grab: audio stutters after few minutes (fc29+KDE)

kaza · 05-03-2019, 03:13 PM

Hello!

I attempted to grab desktop video+audio using ffmpeg, just like I used to do
long ago (in 2017, since then I updated to fc29, don't remember under what OS
it succeded, maybe fc26).

The problem I'm encountering now: the video is OK, the audio starts OK then, after few minutes
it starts to stutter, then becomes shifted by a VERY LARGE ammount relative to the video then,
I think, it again stutters and shifts more (with different audio encoders it's slightly different)
and finally the the audio ends much earlier than video.

The command I used:

ffmpeg -thread_queue_size 512 -f x11grab -s 1906x1038 -r 25 -i :0.0+14,130 -thread_queue_size 512 -f pulse -ac 2 -i alsa_output.pci-0000_00_14.2.analog-stereo.monitor -acodec pcm_s16le -vcodec libx264 -preset ultrafast sample.avi

and the stuttering started after 9 minutes.

With another audio encoder:

ffmpeg -thread_queue_size 512 -f x11grab -s 1906x1038 -r 25 -i :0.0+14,130 -thread_queue_size 512 -f pulse -ac 2 -i alsa_output.pci-0000_00_14.2.analog-stereo.monitor -acodec ac3 -vcodec libx264 -preset ultrafast sample.avi

the stuttering occured after 5.5 minutes.

With the command:

ffmpeg -f x11grab -s 1906x1038 -r 25 -i :0.0+14,130 -f pulse -ac 2 -i alsa_output.pci-0000_00_14.2.analog-stereo.monitor -acodec libmp3lame -vcodec libx264 -preset ultrafast sample.mkv

the audio stops after 2 minutes.

An attempt to use "-f alsa -i hw:0" instead of "-f pulse" resulted in a "silent movie"
and also, I noticed that the files

/proc/asound/cards
/proc/asound/devices

are empty.

Checking for alsa devices of ffmpeg:

Code:

ffmpeg -devices | grep alsa
DE alsa            ALSA audio output

The alsa-related packages:

Code:

<root localhost.localdomain>.../root>rpm -qa | grep alsa
alsa-lib-1.1.8-1.fc29.i686
qemu-audio-alsa-3.0.0-4.fc29.x86_64
alsa-utils-1.1.8-2.fc29.x86_64
alsa-plugins-pulseaudio-1.1.8-1.fc29.x86_64
wine-alsa-4.4-1.fc29.x86_64
alsamixergui-0.9.0-0.27.rc2.fc29.x86_64
alsa-ucm-1.1.8-1.fc29.noarch
alsa-lib-1.1.8-1.fc29.x86_64
wine-alsa-4.4-1.fc29.i686

<root localhost.localdomain>.../root>rpm -ql alsa-lib-1.1.8-1.fc29.i686  | grep libasound
/lib/libasound.so.2
/lib/libasound.so.2.0.0

And I thought that just writng down the command which worked in 2017 would continue to work...

I "googled" and searched LQ for "ffmpeg" but didn't find anything relevant and RECENT - old
solutions might not work now. Does anyone have an idea why in FC29+KDE the audio grab no longer works
the same as it used to?

TIA,
kaza.

kaza · 05-04-2019, 08:55 AM

Small correction: I erroneously thought that

/proc/asound/cards
/proc/asound/devices

are empty because I did "ls -l" on them and saw size of zero
and when I attempted to open then with an editor I saw nothing.

But when I did "more" I saw that they actually hold content:

Code:

<localhost>.../temp>more /proc/asound/cards
 0 [SB             ]: HDA-Intel - HDA ATI SB
                      HDA ATI SB at 0xfe2f4000 irq 16
 1 [HDMI           ]: HDA-Intel - HDA ATI HDMI
                      HDA ATI HDMI at 0xfe3ec000 irq 26
 2 [SAA7134        ]: SAA7134 - SAA7134
                      saa7134[0] at 0xfebffc00 irq 21
<localhost>.../temp>more /proc/asound/devices
  1:        : sequencer
  2: [ 1- 3]: digital audio playback
  3: [ 1- 0]: hardware dependent
  4: [ 1]   : control
  5: [ 0- 0]: digital audio playback
  6: [ 0- 0]: digital audio capture
  7: [ 0- 1]: digital audio playback
  8: [ 0- 2]: digital audio playback
  9: [ 0- 2]: digital audio capture
 10: [ 0- 0]: hardware dependent
 11: [ 0]   : control
 12: [ 2- 0]: digital audio capture
 13: [ 2]   : control
 33:        : timer

Still can't figure out why using "-f pulse" audio stutters after few minutes and using "-f alsa -i hw:0" (or hw:0,0) results in silence...

TIA,
kaza.

ondoho · 05-06-2019, 12:37 AM

Quote:

Originally Posted by kaza

Still can't figure out why using "-f pulse" audio stutters after few minutes and using "-f alsa -i hw:0" (or hw:0,0) results in silence...

with alsa it is extremely tricky if not impossible to record the sound that your system actually emanates.
why it's bumpy with pulse - my guess is there's a bottleneck somewhere, maybe pulse is transcoding the sound and then ffmpeg is trying to transcode it again, maybe ffmpeg is too busy transcoding-on-the-fly thevideo and gives up on the sound ... who knows.

maybe ffmpeg has a verbose flag (actually i know it has and it can be fine-tuned if you know what you're looking for) to get more output, maybe pulseaudio logs something too.

maybe you should start from scratch: make a web search for how to do what you want to do, make sure the results are current - maybe it's a slightly different command?

kaza · 05-06-2019, 04:07 PM

Hi ondoho, thanks for the reply.

I'll stop attempts to use ALSA and will concentrate on "Pulse".
I used video output format of AVI as I thought it'll be less CPU-intensive
compared with MP4, although "-vcodec libx264" might add some CPU-load.

Now, after specifically searching for lowest CPU usage for ffmpeg
I found a suggested command:

ffmpeg -y -framerate 25 -video_size 1280x1024 -f x11grab -i :0.0 -c:v libx264rgb \
-crf 0 -preset ultrafast temp.mp4

I'll try using the libx264rgb instead of libx264.

Thanks,
kaza.