FFMPEG video is out of sync

dermetfan · 08-25-2013, 12:23 PM

Hi everyone!
I'm trying to use ffmpeg to record my desktop. It's working with both audio and video, but no matter which options I use, the video is always out of sync. It's always too fast or too slow, sometimes even changing during one recording.

I used these commands among many others, but always the same result:

Code:

ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1920x1080 -i :0.0 -acodec pcm_s16le -vcodec libx264 -preset ultrafast -crf 0 -threads 0 -y screencast_out.avi

Code:

ffmpeg -f alsa -ac 2 -ar 44100 -i pulse -f x11grab -r 15 -s 1920x1080 -i :0.0 -vcodec h264 -r 15 -sameq out.avi

I noticed the lines

Code:

[alsa @ 0xb5dba0] Estimating duration from bitrate, this may be inaccurate

Code:

[x11grab @ 0xb41500] Estimating duration from bitrate, this may be inaccurate

maybe they have something to do with it. The audio is working fine so I guess only the x11grab warning is of interest.

Here's the whole output for the second command, in case you need it:

Code:

dermetfan@dermetfan ~ $ ffmpeg -f alsa -ac 2 -ar 44100 -i pulse -f x11grab -r 15 -s 1920x1080 -i :0.0 -vcodec h264 -r 15 -sameq out.avi
ffmpeg version 1.0 Copyright (c) 2000-2012 the FFmpeg developers
  built on Nov 17 2012 11:28:48 with gcc 4.7 (Debian 4.7.2-4)
  configuration: --prefix=/usr --extra-cflags='-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security ' --extra-ldflags='-Wl,-z,relro' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-nonfree --disable-decoder=libdirac --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-libvpx --enable-librtmp --enable-avfilter --enable-libfreetype --enable-libvo-aacenc --disable-decoder=amrnb --enable-libvo-amrwbenc --enable-libaacplus --libdir=/usr/lib/x86_64-linux-gnu --disable-vda --enable-libbluray --enable-libcdio --enable-gnutls --enable-frei0r --enable-openssl --enable-libass --enable-libopus --enable-fontconfig --enable-libdc1394 --disable-altive  libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[alsa @ 0x19b7ba0] Estimating duration from bitrate, this may be inaccurate
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, alsa, from 'pulse':
  Duration: N/A, start: 1377451261.923471, bitrate: 1411 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
[x11grab @ 0x199b680] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 1920 height: 1080
[x11grab @ 0x199b680] shared memory extension found
[x11grab @ 0x199b680] Estimating duration from bitrate, this may be inaccurate
Input #1, x11grab, from ':0.0':
  Duration: N/A, start: 1377451262.003424, bitrate: 995328 kb/s
    Stream #1:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080, 995328 kb/s, 15 tbr, 1000k tbn, 15 tbc
File 'out.avi' already exists. Overwrite ? [y/N] y
using cpu capabilities: MMX2 SSE2Fast SSSE3 Cache64
[libx264 @ 0x19b94c0] profile High 4:4:4 Predictive, level 4.0, 4:4:4 8-bit
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf54.29.104
    Stream #0:0: Video: h264 (H264 / 0x34363248), yuv444p, 1920x1080, q=-1--1, 15 tbn, 15 tbc
    Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 44100 Hz, stereo, s16
Stream mapping:
  Stream #1:0 -> #0:0 (rawvideo -> libx264)
  Stream #0:0 -> #0:1 (pcm_s16le -> libmp3lame)
Press [q] to stop, [?] for help
frame=   12 fps=0.0 q=0.0 size=      10kB time=00:00:00.00 bitrate=   0.0kbits/sframe=   23 fps= 22 q=0.0 size=      10kB time=00:00:00.80 bitrate=  97.9kbits/sframe=   31 fps= 20 q=0.0 size=      10kB time=00:00:02.58 bitrate=  30.7kbits/sframe=   32 fps=8.5 q=32766.0 Lsize=     501kB time=00:00:02.71 bitrate=1511.6kbits/s    
video:406kB audio:83kB subtitle:0 global headers:0kB muxing overhead 2.665515%
[libx264 @ 0x19b94c0] frame I:1     Avg QP:20.01  size:278616
[libx264 @ 0x19b94c0] frame P:8     Avg QP:23.55  size: 12353
[libx264 @ 0x19b94c0] frame B:23    Avg QP:20.86  size:  1653
[libx264 @ 0x19b94c0] consecutive B-frames:  3.1%  0.0%  9.4% 87.5%
[libx264 @ 0x19b94c0] mb I  I16..4: 61.5%  5.0% 33.5%
[libx264 @ 0x19b94c0] mb P  I16..4:  1.4%  0.1%  0.9%  P16..4:  3.2%  0.6%  0.4%  0.0%  0.0%    skip:93.3%
[libx264 @ 0x19b94c0] mb B  I16..4:  0.1%  0.1%  0.1%  B16..8:  3.2%  0.1%  0.1%  direct: 0.0%  skip:96.3%  L0:42.9% L1:56.5% BI: 0.6%
[libx264 @ 0x19b94c0] 8x8 transform intra:6.0% inter:40.6%
[libx264 @ 0x19b94c0] coded y,u,v intra: 26.4% 21.4% 19.6% inter: 0.4% 0.1% 0.1%
[libx264 @ 0x19b94c0] i16 v,h,dc,p: 55% 44%  1%  0%
[libx264 @ 0x19b94c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 32% 30% 29%  1%  2%  1%  2%  1%  3%
[libx264 @ 0x19b94c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 34% 15%  2%  3%  3%  5%  3%  4%
[libx264 @ 0x19b94c0] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x19b94c0] ref P L0: 46.9%  9.3% 31.5% 12.3%
[libx264 @ 0x19b94c0] ref B L0: 67.1% 31.3%  1.6%
[libx264 @ 0x19b94c0] ref B L1: 95.1%  4.9%
[libx264 @ 0x19b94c0] kb/s:1557.98

Does anyone have an idea what might be causing this? Thanks!

teckk · 08-25-2013, 01:24 PM

Quote:

ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1920x1080 -i :0.0 -acodec pcm_s16le -vcodec libx264 -preset ultrafast -crf 0 -threads 0 -y screencast_out.avi

Quote:

-r 30 -s 1920x1080

That's huge and 30 fps too. Lower the frames per second, lower the bitrate, capture only part of the desktop that you want seen at a time, don't encode sound and video on the fly,..you also don't say how good a machine you have.

With a 2 core AMD I just did this example with no problem.

Code:

ffmpeg -f alsa -i hw:0,0 -f x11grab -r 24 -s 1000x600 -i :0.0+10,40 -c:a libmp3lame -b:a 32k -c:v libx264 -b:v 500k output.avi

Depends on what you are grabbing. If you are grabbing a terminal while you type you can get away with 15fps, 500K video, if you are talking into a mic while instructing then you can get away with 22050Hz, 32k audio

dermetfan · 08-25-2013, 03:14 PM

I tried with 12 to 30 frames per second, makes no difference. Changed resolution but it also doesn't make any difference, I need to capture the full screen anyway.
My machine is fast enough, it runs normally while I'm recording.

H_TeXMeX_H · 08-26-2013, 02:10 AM

How is the video out of sync exactly ? You mean out of sync with the audio or does it stutter ?

Add this to the command:

Code:

-ar 48000 -async 48000

dermetfan · 08-26-2013, 05:45 AM

It doesn't stutter, it plays smoothly but faster or slower than the audio. So yes, it's out of sync with the audio.
Unfortunately -ar 48000 -async 48000 didn't change anything :/

H_TeXMeX_H · 08-26-2013, 05:54 AM

Try the various '-vsync' options listed here:
http://ffmpeg.org/ffmpeg.html

dermetfan · 08-26-2013, 07:30 AM

Thanks for the help so far! The "drop" option makes it a bit better, but it slowly get's out of sync more over time. The first two minutes are ok, then it worsens.

H_TeXMeX_H · 08-26-2013, 08:22 AM

Maybe try a different audio codec, like vorbis or aac.

dermetfan · 08-26-2013, 09:30 AM

Tried different audio codecs with and without -vsync drop, looks like it's unstoppable on my machine..

CrackerPunk · 08-26-2013, 09:30 AM

I use this for my full screencast and audio and video are in sync

Code:

nice -n 0 ffmpeg -f x11grab  -r 29.970 -s 1280x1024 -i :0.0 -vcodec rawvideo -pix_fmt yuv420p -qscale 1  -threads 4 -acodec pcm_s16le -f alsa -i pulse -y mydesktop.avi

The video quality is not as great as 1080p but the video quality is good and clear enough to see everything including texts.

dermetfan · 08-26-2013, 10:09 AM

Thanks

It gave me Option pixel_format not found.. When I removed -pix_fmt yuv420p it worked, but got out of sync after three minutes :/

CrackerPunk · 08-26-2013, 10:15 AM

That is weird. You seem to have an unusual case with ffmpeg.

I don't have any other ideas. But if I do, I'll post.

teckk · 08-26-2013, 10:35 AM

Yes, that worked fine. Makes a huge file that you can re-encode later. 9 seconds makes a 650MB file.

Code:

ffmpeg -f alsa -i hw:0,0 -c:a pcm_s16le -f x11grab -r 24 -s 1920x1080 -i :0.0 -c:v rawvideo -pix_fmt yuv420p output.avi

You could also scale it down

Code:

ffmpeg -f alsa -i hw:0,0 -c:a pcm_s16le -f x11grab -r 24 -s 1920x1080 -i :0.0 -c:v rawvideo -pix_fmt yuv420p -s 960x540 output.avi

I hadn't done this for a while so I set my machine up to see what I came up with. This is on an AMDx2.
I captured video as I narrated into the mic.

Code:

ffmpeg -f alsa -i hw:0,0 -f x11grab -r 10 -s 1920x1080 -i 0:0 -c:a libmp3lame -b:a 32k -c:v libx264 -b:v 500k -s 960x540 output.avi

I ran that for 3 min, the audio-video did not loose sync, and the file size is 8MB.

CrackerPunk · 08-26-2013, 11:41 AM

Perhaps it's the version of ffmpeg he has, just my guess.

The switches and parameters can have different outcomes based on the version of ffmpeg and how it was compiled by the distro.

Maybe he can try avconv. Avconv is compatible with ffmpeg switches.

@ dermetfan

You said you have a fast system, can you post the specs of your machine and the type of video card.

dermetfan · 08-26-2013, 12:58 PM

Now that's really weird. I modified teckk's last line a bit to work on my sytem (syntax errors) and it just records a part of the screen (even though I additionally set it to 1920x1080 everywhere), but is still in sync after 3:42 minutes (10.4 MB):

Code:

ffmpeg -f alsa -i pulse -f x11grab -i :0.0 -r 10 -s 1920x1080 -c:a libmp3lame -b:a 32k -c:v libx264 -b:v 500k -s 1920x1080 output.avi

I can't record video using avconv though, can I? Also I'd like to stream to an rtmp server later...

Well I said the system was fast enough... At least there were no noticeable lags or slowdowns while recording.
Video card: NVidia 9600 GT
CPU: Intel Core2 CPU 6600 @ 2.40GHz (that might be a bit rusty)
Memory: 4GB