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Thread: HOWTO: Proper Screencasting on Linux

  1. #241
    Join Date
    Dec 2013
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    Re: HOWTO: Proper Screencasting on Linux

    Quote Originally Posted by alanpotteiger View Post
    Hello! I'm not a very experienced person with this type of thing. I have followed the tutorial and have successfully recorded my screen with audio from my microphone, with one problem. For some reason the audio from my microphone is not synced with the video, Is this a common ocurrence? Any fixes or ideas? Thanks!
    Sorry for the double post.
    I have partially fixed the problem. I have the audio in sync but only by decreasing the frame rate from 30 to 24. This will work but is there a reason it didn't work at 30?

  2. #242
    Join Date
    Sep 2006
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    Re: HOWTO: Proper Screencasting on Linux

    Please show your ffmpeg command and the complete ffmpeg console output. Does it make a difference if you replace "-r" with "-framerate"?

  3. #243
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    Dec 2013
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    Re: HOWTO: Proper Screencasting on Linux

    Quote Originally Posted by FakeOutdoorsman View Post
    Please show your ffmpeg command and the complete ffmpeg console output. Does it make a difference if you replace "-r" with "-framerate"?
    Thanks for the response! My command:
    Code:
    ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 24 -s 1920x1080 -i :0.0 -acodec pcm_s16le -vcodec libx264 -preset ultrafast -crf 0 -threads 0 output.mkv
    Also it should be noted that decreasing the fps to 24 did not completely fix the problem... It's 50/50 sometimes it's in sync and sometimes it's not, very odd.
    Output:
    Code:
    ffmpeg version git-2013-12-27-42b6805 Copyright (c) 2000-2013 the FFmpeg developers
      built on Dec 26 2013 20:44:39 with gcc 4.7 (Ubuntu/Linaro 4.7.3-1ubuntu1)
      configuration: --prefix=/home/apott/ffmpeg_build --extra-cflags=-I/home/apott/ffmpeg_build/include --extra-ldflags=-L/home/apott/ffmpeg_build/lib --bindir=/home/apott/bin --extra-libs=-ldl --enable-gpl --enable-libass --enable-libfdk-aac --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-x11grab
      libavutil      52. 59.100 / 52. 59.100
      libavcodec     55. 46.100 / 55. 46.100
      libavformat    55. 22.100 / 55. 22.100
      libavdevice    55.  5.102 / 55.  5.102
      libavfilter     4.  0.103 /  4.  0.103
      libswscale      2.  5.101 /  2.  5.101
      libswresample   0. 17.104 /  0. 17.104
      libpostproc    52.  3.100 / 52.  3.100
    Guessed Channel Layout for  Input Stream #0.0 : stereo
    Input #0, alsa, from 'pulse':
      Duration: N/A, start: 1388124885.639449, bitrate: 1536 kb/s
        Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
    [x11grab @ 0x1bf2c20] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 1920 height: 1080
    [x11grab @ 0x1bf2c20] shared memory extension found
    Input #1, x11grab, from ':0.0':
      Duration: N/A, start: 1388124885.695288, bitrate: 1592524 kb/s
        Stream #1:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080, 1592524 kb/s, 24 tbr, 1000k tbn, 24 tbc
    No pixel format specified, yuv444p for H.264 encoding chosen.
    Use -pix_fmt yuv420p for compatibility with outdated media players.
    [libx264 @ 0x1c09680] using cpu capabilities: MMX2 SSE2Fast SSSE3 Cache64
    [libx264 @ 0x1c09680] profile High 4:4:4 Predictive, level 4.0, 4:4:4 8-bit
    [libx264 @ 0x1c09680] 264 - core 140 r2 1ca7bb9 - H.264/MPEG-4 AVC codec - Copyleft 2003-2013 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=0 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=0 chroma_qp_offset=0 threads=3 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=24 scenecut=0 intra_refresh=0 rc=cqp mbtree=0 qp=0
    Output #0, matroska, to 'output.mkv':
      Metadata:
        encoder         : Lavf55.22.100
        Stream #0:0: Video: h264 (libx264) (H264 / 0x34363248), yuv444p, 1920x1080, q=-1--1, 1k tbn, 24 tbc
        Stream #0:1: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s16, 1536 kb/s
    Stream mapping:
      Stream #1:0 -> #0:0 (rawvideo -> libx264)
      Stream #0:0 -> #0:1 (pcm_s16le -> pcm_s16le)
    Press [q] to stop, [?] for help
    frame=  129 fps= 24 q=-1.0 Lsize=    2749kB time=00:00:05.37 bitrate=4189.9kbits/s    
    video:1717kB audio:1003kB subtitle:0 global headers:0kB muxing overhead 1.082968%
    [libx264 @ 0x1c09680] frame I:1     Avg QP: 0.00  size:426614
    [libx264 @ 0x1c09680] frame P:128   Avg QP: 0.00  size: 10396
    [libx264 @ 0x1c09680] mb I  I16..4: 100.0%  0.0%  0.0%
    [libx264 @ 0x1c09680] mb P  I16..4: 63.8%  0.0%  0.0%  P16..4:  0.0%  0.0%  0.0%  0.0%  0.0%    skip:36.1%
    [libx264 @ 0x1c09680] coded y,u,v intra: 0.3% 0.3% 0.3% inter: 0.0% 0.0% 0.0%
    [libx264 @ 0x1c09680] i16 v,h,dc,p: 100%  0%  0%  0%
    [libx264 @ 0x1c09680] kb/s:2615.57

  4. #244
    Join Date
    Sep 2006
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    3,490

    Re: HOWTO: Proper Screencasting on Linux

    It's good you're using a recent and real build of ffmpeg.

    1. Have you tried using -framerate instead of -r?

    2. What if you capture video and audio as separate processes and remux? (The following is untested)
    Code:
    ffmpeg -f x11grab -framerate 24 -video_size 1920x1080 -i :0.0 -vcodec libx264 -preset ultrafast -crf 0 -t 60 v.mkv & \
    ffmpeg -f alsa -ac 2 -i pulse -acodec copy -t 60 a.wav && fg; \
    ffmpeg -i v.mkv -i a.wav -c copy -shortest muxed.mkv
    3. What player are you using so you know it is not in sync?

    4. Is it better if you re-encode the original, out-of-sync output?
    Code:
    ffmpeg -i output.mkv -vf scale=640:-1 -crf 18 -preset medium -pix_fmt yuv420p -c:a copy output.mkv
    Last edited by FakeOutdoorsman; December 27th, 2013 at 08:51 AM.

  5. #245
    Join Date
    Dec 2013
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    4

    Re: HOWTO: Proper Screencasting on Linux

    Quote Originally Posted by FakeOutdoorsman View Post
    1. Have you tried using -framerate instead of -r?
    Turns out that right there fixed it! Thanks for the help.
    And if you're curious I upload the clips to Youtube to verify it's not my viewer making it out of sync.
    Thanks again!

  6. #246
    Join Date
    Jan 2014
    Beans
    1

    Re: HOWTO: Proper Screencasting on Linux

    Hello all,

    First of all, sorry if the information I'm sharing is not related with the topic.
    With some coworkers we are developing a tool to replace Jing for ubuntu. Is free and the source code is in bitbucket https://bitbucket.org/msbrocca/screen-capturer

    So far we are just capturing screen parts to save or share. We have an open branch to work on video capturing.

    Feel free to take a look and use it.
    Regards,
    Maxi

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