OK. I found how to stop having this "ALSA buffer xrun" message: 1) when the output is a file on a local directory, you just need to change the command: $ ffmpeg -y -f alsa -i default -f x11grab -r 10 -s 640x480 -async 1 -i :0.0 -strict -2 -c:a aac -c:v libx264 -pix_fmt yuv420p -preset ultrafast -s 640x480 -threads 0 -ar 44100 -b:a 64k -b:v 64k -bufsize 64k -f flv out.flv 2) when the output is a file on a NFS shared directory, you need to change the command like above and update the x264 library from 20120729.2245 to 20140207.2245 [1]. 3) when the output is a stream on twitch.tv, you need to change the command like above, you need to update x264 like above, but there is a remaining "ALSA buffer xrun" message at the beginning of the capture.
For 3) the problem could be caused by rtmp "handshake" which is 3 (see section 5.2 of [2]). My command is: $ ffmpeg -y -f alsa -i default -f x11grab -r 10 -s 640x480 -async 1 -i :0.0 -strict -2 -c:a aac -c:v libx264 -pix_fmt yuv420p -preset ultrafast -s 640x480 -threads 0 -ar 44100 -b:a 64k -b:v 64k -bufsize 64k -f flv "rtmp://live-fra.twitch.tv/app/`cat ~/twitch.key`" And I can see: $ cat /proc/asound/card0/pcm0c/sub0/hw_params access: MMAP_INTERLEAVED format: S32_LE subformat: STD channels: 2 rate: 48000 (48000/1) period_size: 1024 buffer_size: 16384 So, my buffer time is: 16384/48000 = 0.34. Now, I need to take the RTT from live-fra.twitch.tv, multiply by 3 and this value must be smaller than 0.34 (my buffer time above). The problem is that live-fra.twitch.tv refuse the ping. So, I can use tcpdump: $ sudo tcpdump -ni eth0 host live-fra.twitch.tv tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 22:21:12.644355 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [S], seq 2241789542, win 14600, options [mss 1460,sackOK,TS val 37145446 ecr 0,nop,wscale 7], length 0 22:21:12.695150 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [S.], seq 2043124064, ack 2241789543, win 5792, options [mss 1436,sackOK,TS val 1662742014 ecr 37145446,nop,wscale 9], length 0 22:21:12.695178 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], ack 1, win 115, options [nop,nop,TS val 37145497 ecr 1662742014], length 0 22:21:12.695386 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 1:1425, ack 1, win 115, options [nop,nop,TS val 37145498 ecr 1662742014], length 1424 22:21:12.695439 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 1425:1538, ack 1, win 115, options [nop,nop,TS val 37145498 ecr 1662742014], length 113 22:21:12.757727 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 1425, win 17, options [nop,nop,TS val 1662742020 ecr 37145498], length 0 22:21:12.759387 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 1538, win 17, options [nop,nop,TS val 1662742020 ecr 37145498], length 0 22:21:13.120657 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], seq 1:1425, ack 1538, win 17, options [nop,nop,TS val 1662742056 ecr 37145498], length 1424 22:21:13.120676 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], ack 1425, win 137, options [nop,nop,TS val 37145923 ecr 1662742056], length 0 22:21:13.122851 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [P.], seq 1425:3074, ack 1538, win 17, options [nop,nop,TS val 1662742056 ecr 37145498], length 1649 22:21:13.122861 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], ack 3074, win 163, options [nop,nop,TS val 37145925 ecr 1662742056], length 0 22:21:13.122886 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 1538:2962, ack 3074, win 163, options [nop,nop,TS val 37145925 ecr 1662742056], length 1424 22:21:13.122891 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 2962:3074, ack 3074, win 163, options [nop,nop,TS val 37145925 ecr 1662742056], length 112 22:21:13.186668 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 2962, win 23, options [nop,nop,TS val 1662742063 ecr 37145925], length 0 22:21:13.187108 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3074, win 23, options [nop,nop,TS val 1662742063 ecr 37145925], length 0 22:21:13.187120 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 3074:3233, ack 3074, win 163, options [nop,nop,TS val 37145989 ecr 1662742063], length 159 22:21:13.238634 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3233, win 29, options [nop,nop,TS val 1662742068 ecr 37145989], length 0 22:21:13.428350 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [P.], seq 3074:3414, ack 3233, win 29, options [nop,nop,TS val 1662742087 ecr 37145989], length 340 22:21:13.428512 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 3233:3245, ack 3414, win 185, options [nop,nop,TS val 37146231 ecr 1662742087], length 12 22:21:13.479104 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3245, win 29, options [nop,nop,TS val 1662742092 ecr 37146231], length 0 22:21:13.479122 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 3245:3440, ack 3414, win 185, options [nop,nop,TS val 37146281 ecr 1662742092], length 195 22:21:13.531599 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3440, win 34, options [nop,nop,TS val 1662742097 ecr 37146281], length 0 22:21:13.720507 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [P.], seq 3414:3643, ack 3440, win 34, options [nop,nop,TS val 1662742116 ecr 37146281], length 229 22:21:13.720645 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 3440:3452, ack 3643, win 207, options [nop,nop,TS val 37146523 ecr 1662742116], length 12 22:21:13.769840 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3452, win 34, options [nop,nop,TS val 1662742121 ecr 37146523], length 0 22:21:13.769858 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 3452:3526, ack 3643, win 207, options [nop,nop,TS val 37146572 ecr 1662742121], length 74 22:21:13.820389 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3526, win 34, options [nop,nop,TS val 1662742126 ecr 37146572], length 0 22:21:14.376738 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [P.], seq 3643:3661, ack 3526, win 34, options [nop,nop,TS val 1662742182 ecr 37146572], length 18 22:21:14.377239 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [P.], seq 3661:3812, ack 3526, win 34, options [nop,nop,TS val 1662742182 ecr 37146572], length 151 22:21:14.377272 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], ack 3812, win 230, options [nop,nop,TS val 37147179 ecr 1662742182], length 0 22:21:14.479079 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 3526:3538, ack 3812, win 230, options [nop,nop,TS val 37147281 ecr 1662742182], length 12 22:21:14.479876 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 3538:4962, ack 3812, win 230, options [nop,nop,TS val 37147282 ecr 1662742182], length 1424 22:21:14.479955 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 4962:6386, ack 3812, win 230, options [nop,nop,TS val 37147282 ecr 1662742182], length 1424 22:21:14.480013 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 6386:7810, ack 3812, win 230, options [nop,nop,TS val 37147282 ecr 1662742182], length 1424 22:21:14.503009 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 7810:9234, ack 3812, win 230, options [nop,nop,TS val 37147305 ecr 1662742182], length 1424 22:21:14.529153 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 3538, win 34, options [nop,nop,TS val 1662742197 ecr 37147281], length 0 22:21:14.529180 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 9234:9982, ack 3812, win 230, options [nop,nop,TS val 37147331 ecr 1662742197], length 748 22:21:14.542926 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 4962, win 40, options [nop,nop,TS val 1662742199 ecr 37147282], length 0 22:21:14.555229 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 6386, win 46, options [nop,nop,TS val 1662742200 ecr 37147282], length 0 22:21:14.568355 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 7810, win 51, options [nop,nop,TS val 1662742201 ecr 37147282], length 0 22:21:14.581640 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 9234, win 57, options [nop,nop,TS val 1662742202 ecr 37147305], length 0 22:21:14.587551 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 9982, win 62, options [nop,nop,TS val 1662742203 ecr 37147331], length 0 22:21:14.587569 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 9982:10524, ack 3812, win 230, options [nop,nop,TS val 37147390 ecr 1662742203], length 542 22:21:14.642760 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 10524, win 68, options [nop,nop,TS val 1662742208 ecr 37147390], length 0 22:21:14.642783 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 10524:10886, ack 3812, win 230, options [nop,nop,TS val 37147445 ecr 1662742208], length 362 22:21:14.696406 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 10886, win 74, options [nop,nop,TS val 1662742214 ecr 37147445], length 0 22:21:14.696430 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 10886:11523, ack 3812, win 230, options [nop,nop,TS val 37147499 ecr 1662742214], length 637 22:21:14.750972 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 11523:12947, ack 3812, win 230, options [nop,nop,TS val 37147553 ecr 1662742214], length 1424 22:21:14.751087 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 12947:14371, ack 3812, win 230, options [nop,nop,TS val 37147553 ecr 1662742214], length 1424 22:21:14.752174 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 11523, win 79, options [nop,nop,TS val 1662742219 ecr 37147499], length 0 22:21:14.752192 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 14371:15191, ack 3812, win 230, options [nop,nop,TS val 37147554 ecr 1662742219], length 820 22:21:14.815181 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 12947, win 85, options [nop,nop,TS val 1662742226 ecr 37147553], length 0 22:21:14.822662 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 15191:16615, ack 3812, win 230, options [nop,nop,TS val 37147625 ecr 1662742226], length 1424 22:21:14.825566 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 14371, win 90, options [nop,nop,TS val 1662742227 ecr 37147553], length 0 22:21:14.834446 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 15191, win 96, options [nop,nop,TS val 1662742228 ecr 37147554], length 0 22:21:14.834466 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 16615:17456, ack 3812, win 230, options [nop,nop,TS val 37147637 ecr 1662742228], length 841 22:21:14.884980 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 16615, win 102, options [nop,nop,TS val 1662742233 ecr 37147625], length 0 22:21:14.893509 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 17456, win 107, options [nop,nop,TS val 1662742234 ecr 37147637], length 0 22:21:14.893540 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 17456:18418, ack 3812, win 230, options [nop,nop,TS val 37147696 ecr 1662742234], length 962 22:21:14.952716 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 18418, win 113, options [nop,nop,TS val 1662742240 ecr 37147696], length 0 22:21:14.952738 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 18418:18867, ack 3812, win 230, options [nop,nop,TS val 37147755 ecr 1662742240], length 449 22:21:15.006909 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 18867, win 118, options [nop,nop,TS val 1662742245 ecr 37147755], length 0 22:21:15.006935 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 18867:19687, ack 3812, win 230, options [nop,nop,TS val 37147809 ecr 1662742245], length 820 22:21:15.063867 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 19687, win 124, options [nop,nop,TS val 1662742251 ecr 37147809], length 0 22:21:15.063891 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 19687:20408, ack 3812, win 230, options [nop,nop,TS val 37147866 ecr 1662742251], length 721 22:21:15.120557 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 20408, win 126, options [nop,nop,TS val 1662742256 ecr 37147866], length 0 22:21:15.120580 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 20408:20896, ack 3812, win 230, options [nop,nop,TS val 37147923 ecr 1662742256], length 488 22:21:15.174701 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 20896, win 126, options [nop,nop,TS val 1662742262 ecr 37147923], length 0 22:21:15.208000 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 20896:20904, ack 3812, win 230, options [nop,nop,TS val 37148010 ecr 1662742262], length 8 22:21:15.258457 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 20904, win 126, options [nop,nop,TS val 1662742270 ecr 37148010], length 0 22:21:15.258480 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 20904:21924, ack 3812, win 230, options [nop,nop,TS val 37148061 ecr 1662742270], length 1020 22:21:15.317611 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 21924, win 126, options [nop,nop,TS val 1662742276 ecr 37148061], length 0 22:21:15.317635 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 21924:23184, ack 3812, win 230, options [nop,nop,TS val 37148120 ecr 1662742276], length 1260 22:21:15.378962 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 23184, win 126, options [nop,nop,TS val 1662742282 ecr 37148120], length 0 22:21:15.406632 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 23184:23192, ack 3812, win 230, options [nop,nop,TS val 37148209 ecr 1662742282], length 8 22:21:15.457324 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 23192, win 126, options [nop,nop,TS val 1662742290 ecr 37148209], length 0 22:21:15.457349 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 23192:24478, ack 3812, win 230, options [nop,nop,TS val 37148259 ecr 1662742290], length 1286 22:21:15.518648 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 24478, win 126, options [nop,nop,TS val 1662742296 ecr 37148259], length 0 22:21:15.518671 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 24478:25845, ack 3812, win 230, options [nop,nop,TS val 37148321 ecr 1662742296], length 1367 22:21:15.581263 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 25845, win 126, options [nop,nop,TS val 1662742302 ecr 37148321], length 0 22:21:15.606279 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 25845:25853, ack 3812, win 230, options [nop,nop,TS val 37148408 ecr 1662742302], length 8 22:21:15.656219 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 25853, win 126, options [nop,nop,TS val 1662742310 ecr 37148408], length 0 22:21:15.656241 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 25853:26782, ack 3812, win 230, options [nop,nop,TS val 37148458 ecr 1662742310], length 929 22:21:15.706905 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [.], seq 26782:28206, ack 3812, win 230, options [nop,nop,TS val 37148509 ecr 1662742310], length 1424 22:21:15.714573 IP 199.9.254.236.1935 > 192.168.0.2.42053: Flags [.], ack 26782, win 126, options [nop,nop,TS val 1662742316 ecr 37148458], length 0 22:21:15.714593 IP 192.168.0.2.42053 > 199.9.254.236.1935: Flags [P.], seq 28206:28277, ack 3812, win 230, options [nop,nop,TS val 37148517 ecr 1662742316], length 71 ^C 86 packets captured 92 packets received by filter 0 packets dropped by kernel Do you see the RTT value here? [1] ftp://ftp.videolan.org/pub/videolan/x264/snapshots/ [2] http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/rtmp/pdf/rtmp_specification_1.0.pdf On Thu, 6 Feb 2014 20:14:57 +0100 YuGiOhJCJ Mailing-List <yugiohjcj-mailingl...@laposte.net> wrote: > Hello, > > I am using ffmpeg version 1.2. > > To record (audio/video) my desktop with ffmpeg, I use this command: > $ ffmpeg -f x11grab -r 15 -s 640x480 -i :0.0 -f alsa -i default out.mkv > > Unfortunately, when I am playing this "out.mkv" file on VLC, I can remark > that the audio is out of sync. > > In the console, I can see some warnings: "ALSA buffer xrun". > > Do you see why ? > > Thank you. > Best regards. > > ------------------------------------------------------------------------------ > Managing the Performance of Cloud-Based Applications > Take advantage of what the Cloud has to offer - Avoid Common Pitfalls. > Read the Whitepaper. > http://pubads.g.doubleclick.net/gampad/clk?id=121051231&iu=/4140/ostg.clktrk > _______________________________________________ > Alsa-user mailing list > Alsa-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/alsa-user ------------------------------------------------------------------------------ Flow-based real-time traffic analytics software. Cisco certified tool. Monitor traffic, SLAs, QoS, Medianet, WAAS etc. with NetFlow Analyzer Customize your own dashboards, set traffic alerts and generate reports. Network behavioral analysis & security monitoring. All-in-one tool. http://pubads.g.doubleclick.net/gampad/clk?id=126839071&iu=/4140/ostg.clktrk _______________________________________________ Alsa-user mailing list Alsa-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/alsa-user
