[LAU] [LAD] Screencasting with JACK [SOLVED!]

[Peder Hedlund]

Quoting Diego Simak <diego.simak at gmail.com>:

> - Audio and video are not in sync, I can see the following message
> after executing the ffmpeg command:
>
> [swscaler @ 0x1ac5080] Warning: data is not aligned! This can lead to
> a speedloss
>
> diego at ruidosa:~$ ffmpeg -fflags +genpts+igndts -f x11grab -vsync 0 -r
> 30 -s 1366x768 -i :0.0+0,0 -vcodec h264 -f jack -ac 2 -r:a 48000  -i
> screencast -acodec pcm_s16le -r:v 30 -vsync 2 -async 1 -map 0:0,1,0
> -map 1:0 -preset ultrafast -qp 0 aaa.mkv

>   Duration: N/A, start: 1376226919.464630, bitrate: 1007124 kb/s
>     Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1366x768,
> 1007124 kb/s, 30 tbr, 1000k tbn, 30 tbc
> jack_port_get_latency_range called with an incorrect port 0
> [jack @ 0x1afbce0] JACK client registered and activated (rate=48000Hz,
> buffer_size=1024 frames)
> Guessed Channel Layout for  Input Stream #1.0 : stereo
> Input #1, jack, from 'screencast':
>   Duration: N/A, start: 1376226919.619355, bitrate: 3072 kb/s
>     Stream #1:0: Audio: pcm_f32le, 48000 Hz, stereo, flt, 3072 kb/s
> [swscaler @ 0x1ac5080] Warning: data is not aligned! This can lead to
> a speedloss
> frame=  122 fps= 23 q=-1.0 Lsize=    2774kB time=00:00:04.06
> bitrate=5588.3kbits/s
> video:2040kB audio:732kB subtitle:0 global headers:0kB muxing   
> overhead 0.097703%

A couple of things :

* 1366 isn't a multiple of 8 which is probably why you get the "data  
is not aligned! This can lead to a speedloss" warning. Set it to 1360  
instead.

* You've set ffmpeg to record at 30 fps but it seems your computer can  
only manage to do 23 fps. That might be the cause of the A/V being out  
of sync.
Either decrease the capture area, change "-r:v 30" to something like  
"-r:v 20" or try doing an uncompressed recording (replace "-vcodec  
h264 -preset ultrafast -qp 0" with something like "-vcodec huffyuv").  
In the latter case you'll end up with a really big capture file which  
you might want/need to demux, compress and remux afterwards.

  - Peder