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README.audio.md

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AUDIO support

Veejay has limited audio support aka no fancy effects on sound. Despite that, veejay will keep in sync the audio channel's of your clip, and transport it trough JACK - jackaudio.org a famous and robust low latency audio server.

Be sure veejay has NOT been configured without jack support (default jack support is enabled)

$ veejay -B|grep -i jack

If the previous command is mute, you should configure and build veejay-server again.

Veejay only has support for jackd1 (the old jack).

Prepare

You need an AVI file with an audio track encoded in signed PCM WAVE, 44-48Khz, 2 channels (stereo) (16 bit)

For example with ffmpeg/avconv you can use the "PCM signed 16-bit little-endian" codec named "pcm_s16le"

$ ffmpeg -i myvideo.mp4 -q:v 1 -vcodec mjpeg -acodec pcm_s16le -ar 48000 -s 1024x576 myvideo.avi

Your input video myvideo.mp4 will be transcode to mjpeg video codec, using a video quantifier of 1 setting the quality scale (VBR) to best image quality. The pcm_s16le audio codec is selected, for a 48khz sampling rate. Finally the output video myvideo.avi is resized to 1024x576

Run

When you start veejay with a video containing an audio track, the jackd server is automatically started with the default settings. But you may want to have more control.

Start Jack audio

From terminal command, start jackd :

$ jackd -dalsa -P -r48000

Important : Jack audio server must be configured with the same sampling rate as the loaded video files. Consequently, all your video files must have the same sampling rate.

  • 44khz audio files using -r44100 into the previous command line
  • 48khz audio files using -r48000

(An alternative to this to use the qjackctl graphical user interface)

Now, start veejay

$ veejay -m80 /path/to/myvideo.avi

Use the -m command line option to allow veejay to cache video frames when sampling. This will reduce disk latency, allowing for smoother audio playback (especially when used in combination of speed/pitch changes)

The -m command line option is further explained in README memory

Others audio related options

-a/--audio [01]            Enable ( 1 ) or disable ( 0 ) audio. By default, audio is enabled.
   --pace-correction [ms]  Audio pace correction offset in milliseconds
-c/--synchronization [01]  Sync correction off/on (default on)
-r/--audiorate <num>       Set audio rate (defaults to 48Khz)

Nota : The video you start veejay with must contains an audio track, else the jack transport is not started ... even with -a1 option given.

Audio playback problems

Q: What can I do about the warning "Rendering audio/video frame takes too long (measured 44 ms). Can't keep pace with audio!"

A(1): You can start veejay with the -m commandline option. The warnings are less frequent or dissapear when the whole sample is cached in memory.

A(2): You can disable veejay's multithreaded pixel operations:

$ export VEEJAY_MULTITHREAD_TASKS=0
$ veejay -m80 /path/to/mjpeg.avi

A(3): Have a dedicated veejay-server machine and connect with reloaded through the network

A(4): Run with a different video codec or lower the video resolution