Hello,

I'm trying to use ffmpeg to record the computer screen and also audio from 
microfone. Googling I found a lot of "how to". Although I can now record, I do 
have a few questions (3):

1) Using command

$ ffmpeg -thread_queue_size 512 -f alsa -ac 2 -ar 44100 -i hw:0,0 -video_size 
1024x768 -probesize 10M -framerate 30 -thread_queue_size 512 -f x11grab -i :0.0 
-c:a aac -c:v libx264 -vf "format=yuv420p" output.mp4
ffmpeg version N-98341-gcca982ee01 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)
  configuration: --toolchain=hardened --arch=amd64 --enable-gpl 
--disable-stripping --enable-avresample --disable-filter=resample 
--enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom 
--enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca 
--enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig 
--enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm 
--enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg 
--enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg 
--enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr 
--enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame 
--enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack 
--enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid 
--enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal 
--enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm 
--enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 
--enable-shared
  libavutil      56. 55.100 / 56. 55.100
  libavcodec     58. 93.100 / 58. 93.100
  libavformat    58. 47.100 / 58. 47.100
  libavdevice    58. 11.100 / 58. 11.100
  libavfilter     7. 86.100 /  7. 86.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  8.100 /  5.  8.100
  libswresample   3.  8.100 /  3.  8.100
  libpostproc    55.  8.100 / 55.  8.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'hw:0,0':
  Duration: N/A, start: 1593480535.223265, bitrate: 1411 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
Input #1, x11grab, from ':0.0':
  Duration: N/A, start: 1593480535.257288, bitrate: 754974 kb/s
    Stream #1:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1024x768, 754974 
kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #1:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
  Stream #0:0 -> #0:1 (pcm_s16le (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x55a51bf2fb00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 
AVX
[libx264 @ 0x55a51bf2fb00] profile High, level 3.1
[libx264 @ 0x55a51bf2fb00] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC 
codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: 
cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 
psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 
deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 
sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 
constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 
open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 
rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 
ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'output.mp4':
  Metadata:
    encoder         : Lavf58.47.100
    Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), 
yuv420p(progressive), 1024x768, q=-1--1, 30 fps, 15360 tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.93.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    Stream #0:1: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 
128 kb/s
    Metadata:
      encoder         : Lavc58.93.100 aac
frame=   19 fps=0.0 q=0.0 size=       0kB time=00:00:00.00 bitrate=N/A speed=   
frame=   34 fps= 34 q=0.0 size=       0kB time=00:00:00.00 bitrate=N/A speed=   
frame=   49 fps= 32 q=0.0 size=       0kB time=00:00:00.00 bitrate=N/A speed=   
frame=   64 fps= 32 q=29.0 size=       0kB time=00:00:00.39 bitrate=   
1.0kbits/frame=   79 fps= 31 q=29.0 size=       0kB time=00:00:00.90 bitrate=   
0.4kbits/frame=   95 fps= 31 q=29.0 size=       0kB time=00:00:01.40 bitrate=   
0.3kbits/frame=  110 fps= 31 q=29.0 size=       0kB time=00:00:01.90 bitrate=   
0.2kbits/frame=  125 fps= 31 q=29.0 size=       0kB time=00:00:02.40 bitrate=   
0.2kbits/frame=  140 fps= 31 q=29.0 size=       0kB time=00:00:02.92 bitrate=   
0.1kbits/frame=  156 fps= 31 q=29.0 size=       0kB time=00:00:03.43 bitrate=   
0.1kbits/frame=  162 fps= 28 q=-1.0 Lsize=     208kB time=00:00:05.30 bitrate= 
321.1kbits/s speed=0.93x    
video:143kB audio:59kB subtitle:0kB other streams:0kB global headers:0kB muxing 
overhead: 3.221925%
[libx264 @ 0x55a51bf2fb00] frame I:1     Avg QP:18.42  size: 90858
[libx264 @ 0x55a51bf2fb00] frame P:41    Avg QP:13.42  size:  1010
[libx264 @ 0x55a51bf2fb00] frame B:120   Avg QP:18.59  size:   108
[libx264 @ 0x55a51bf2fb00] consecutive B-frames:  1.2%  0.0%  0.0% 98.8%
[libx264 @ 0x55a51bf2fb00] mb I  I16..4: 16.9% 30.2% 53.0%
[libx264 @ 0x55a51bf2fb00] mb P  I16..4:  0.1%  0.1%  0.2%  P16..4:  0.7%  0.2% 
 0.2%  0.0%  0.0%    skip:98.5%
[libx264 @ 0x55a51bf2fb00] mb B  I16..4:  0.3%  0.0%  0.0%  B16..8:  2.0%  0.0% 
 0.0%  direct: 0.0%  skip:97.7%  L0:55.2% L1:44.8% BI: 0.0%
[libx264 @ 0x55a51bf2fb00] 8x8 transform intra:24.1% inter:12.2%
[libx264 @ 0x55a51bf2fb00] coded y,uvDC,uvAC intra: 37.0% 0.2% 0.0% inter: 0.1% 
0.0% 0.0%
[libx264 @ 0x55a51bf2fb00] i16 v,h,dc,p: 55% 36%  3%  5%
[libx264 @ 0x55a51bf2fb00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 33% 32% 21%  1%  4%  
2%  4%  0%  4%
[libx264 @ 0x55a51bf2fb00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 42% 27%  9%  3%  4%  
4%  4%  4%  4%
[libx264 @ 0x55a51bf2fb00] i8c dc,h,v,p: 97%  3%  0%  0%
[libx264 @ 0x55a51bf2fb00] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x55a51bf2fb00] ref P L0: 87.1%  5.6%  5.9%  1.5%
[libx264 @ 0x55a51bf2fb00] ref B L0: 22.1% 77.3%  0.6%
[libx264 @ 0x55a51bf2fb00] ref B L1: 95.8%  4.2%
[libx264 @ 0x55a51bf2fb00] kb/s:215.20
[aac @ 0x55a51bf31200] Qavg: 214.820
Exiting normally, received signal 2.


last 2 seconds of output.mp4 has no sound at all. Similar issue reported at 


#5900 (alsa/pulse grab cuts last 2 seconds of audio) – FFmpeg


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#5900 (alsa/pulse grab cuts last 2 seconds of audio) – FFmpeg


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To diminish the issue, I added "-preset ultrafast" to the above command and now 
the only last 0.2s has no sound (fine with this)


Question: is there a reason for this "sound issue" when ultrafast is not used?

2) Is this the correct way to use Hardware Aceleration? 

$ ffmpeg -thread_queue_size 512 -f alsa -ac 2 -ar 44100 -i hw:0,0 -vaapi_device 
/dev/dri/renderD128 -video_size 1024x768 -probesize 10M -framerate 30 
-thread_queue_size 512 -f x11grab -i :0.0 -c:a aac -c:v h264_vaapi -vf 
"format=nv12,hwupload" output_hw.mp4
ffmpeg version N-98341-gcca982ee01 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)
  configuration: --toolchain=hardened --arch=amd64 --enable-gpl 
--disable-stripping --enable-avresample --disable-filter=resample 
--enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom 
--enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca 
--enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig 
--enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm 
--enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg 
--enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg 
--enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr 
--enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame 
--enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack 
--enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid 
--enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal 
--enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm 
--enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 
--enable-shared
  libavutil      56. 55.100 / 56. 55.100
  libavcodec     58. 93.100 / 58. 93.100
  libavformat    58. 47.100 / 58. 47.100
  libavdevice    58. 11.100 / 58. 11.100
  libavfilter     7. 86.100 /  7. 86.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  8.100 /  5.  8.100
  libswresample   3.  8.100 /  3.  8.100
  libpostproc    55.  8.100 / 55.  8.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'hw:0,0':
  Duration: N/A, start: 1593480832.865073, bitrate: 1411 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
Input #1, x11grab, from ':0.0':
  Duration: N/A, start: 1593480832.898990, bitrate: 754974 kb/s
    Stream #1:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1024x768, 754974 
kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #1:0 -> #0:0 (rawvideo (native) -> h264 (h264_vaapi))
  Stream #0:0 -> #0:1 (pcm_s16le (native) -> aac (native))
Press [q] to stop, [?] for help
[h264_vaapi @ 0x55b46c504a80] No quality level set; using default (20).
Output #0, mp4, to 'output_hw.mp4':
  Metadata:
    encoder         : Lavf58.47.100
    Stream #0:0: Video: h264 (h264_vaapi) (High) (avc1 / 0x31637661), 
vaapi_vld(progressive), 1024x768, q=-1--1, 30 fps, 15360 tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.93.100 h264_vaapi
    Stream #0:1: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 
128 kb/s
    Metadata:
      encoder         : Lavc58.93.100 aac
frame=   19 fps=0.0 q=-0.0 size=       0kB time=00:00:00.51 bitrate=   
0.8kbits/frame=   34 fps= 33 q=-0.0 size=       0kB time=00:00:01.00 bitrate=   
0.4kbits/frame=   49 fps= 32 q=-0.0 size=     256kB time=00:00:01.53 
bitrate=1368.7kbits/frame=   65 fps= 32 q=-0.0 size=     256kB time=00:00:02.04 
bitrate=1026.5kbits/frame=   80 fps= 32 q=-0.0 size=     256kB time=00:00:02.53 
bitrate= 828.0kbits/frame=   95 fps= 31 q=-0.0 size=     256kB time=00:00:03.04 
bitrate= 689.6kbits/frame=  110 fps= 31 q=-0.0 size=     256kB time=00:00:03.53 
bitrate= 593.6kbits/frame=  125 fps= 31 q=-0.0 size=     512kB time=00:00:04.04 
bitrate=1038.2kbits/frame=  140 fps= 31 q=-0.0 size=     512kB time=00:00:04.57 
bitrate= 917.0kbits/frame=  155 fps= 31 q=-0.0 size=     512kB time=00:00:05.06 
bitrate= 828.7kbits/frame=  171 fps= 31 q=-0.0 size=     768kB time=00:00:05.57 
bitrate=1129.0kbits/frame=  186 fps= 31 q=-0.0 size=     768kB time=00:00:06.06 
bitrate=1037.1kbits/frame=  201 fps= 30 q=-0.0 size=     768kB time=00:00:06.59 
bitrate= 954.1kbits/frame=  217 fps= 31 q=-0.0 size=     768kB time=00:00:07.10 
bitrate= 885.5kbits/frame=  232 fps= 31 q=-0.0 size=     768kB time=00:00:07.60 
bitrate= 827.9kbits/frame=  237 fps= 30 q=-0.0 Lsize=    1029kB 
time=00:00:07.83 bitrate=1076.3kbits/s speed=   1x    
video:896kB audio:123kB subtitle:0kB other streams:0kB global headers:0kB 
muxing overhead: 1.009003%
[aac @ 0x55b46c505bc0] Qavg: 214.335
Exiting normally, received signal 2.

3) Are those commands above "correct"? I mean, is there something "wrong" or 
can it be improved to reduce file size, improve video quality or sound quality? 
I know that ffmpeg has tons of options and "improve" is not a clear question.


Kind regards,
Leonardo
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