HOWTO: Proper Screencasting on Linux

[nehaljwani]

To view the method mentioned above in action, visit:

https://www.youtube.com/watch?v=B-ry-f3Mpx4

[nehaljwani]

Visit: http://www.commandlinefu.com/command.../sort-by-votes

[FakeOutdoorsman]

To view the method mentioned above in action, visit:

https://www.youtube.com/watch?v=B-ry-f3Mpx4

Do not use the -sameq option when using x11grab. See sameq does not mean "same quality".

[rulet]

So, how to do screencast with ffmpeg with simultaneous capturing internal(which goes to speakers) and with external(which recorded by microphone) sound?

[dannyboy79]

So, how to do screencast with ffmpeg with simultaneous capturing internal(which goes to speakers) and with external(which recorded by microphone) sound?

using pavucontrol and all streams. you can create loopbacks so it records both internal audio and mic using pactl, see here for a hint: http://ubuntuforums.org/showthread.p...ghlight=twitch

[dannyboy79]

when trying this

ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1280x720 -i :0.0 -acodec pcm_s16le -vcodec libx264 -preset ultrafast -crf 0 -threads 0 output.mkv

i get this

[matroska @ 0x1668bc0] Application provided invalid, non monotonically increasing dts to muxer in stream 1: 1 >= 1
av_interleaved_write_frame(): Invalid argument

What gives?

[FakeOutdoorsman]

I don't have a "real" solution, but you can output the audio separately and then mux it afterwards. Untested example:

ffmpeg -f x11grab -r 30 -s 1280x720 -i :0.0 -vcodec libx264 -preset ultrafast -crf 0 output-v.mkv -f alsa -ac 2 -i pulse -acodec pcm_s16le output-a.wav
ffmpeg -i output-v.mkv -i output-a.wav -c copy output.mkv

Note that "-threads 0" is default so you don't need to include it.

[VinisLentoje]

Hello!

I've got a bit of a problem with recording - my video & audio get increasingly desynchronized. The longer the video, the longer the gap. For example, in one of the videos I recorded, a couple of minutes in, the video is behind audio by a couple of seconds, @ 1 hour mark - almost a minute, at 2 hour mark - a bit more than two minutes.

I run the capture with

./ffmpeg -f alsa -ac 2 -i pulse -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1280x720 -i +foo,bar -filter_complex amix=inputs=2:duration=first:dropout_transition=3 -acodec pcm_s16le -vcodec libx264 -preset ultrafast -x264opts crf=0 -threads 0 /foo/bar.mkv

I tried running it with -vsync, with aresample=async=1000 audio filter, and tried with both at the same time. Tried recording both audio stream without mixing them on the fly. Tried recording only one audio stream. I still get the same going out of sync problem. Could anyone help me? 'Cause I am out of ideas.

[marvalis]

I seem to have the same problem. Video and audio got out of sync too on my ~40 min video.

[dannyboy79]

i would suggest turning down your frames per second. give that a try