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README.video-codec.md

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Video files

Basic knowledge

A video file consist out of two SEPARATE elements:

  • container
  • codec

The container holds the digitally encoded data and the codec is capable of decoding/encoding this digitally encoded data.

Veejay's file format support

Veejay supports the AVI and the Quicktime container, with the following codecs:

  • Quicktime
    • mpjeg,mjpa,jpeg,dmb1,mpng,png
    • dvsd, dv, dvcp, dvhd
  • AVI
    • mjpeg, mjpa,jpeg,jfif,dmb1,mpng,png
    • dvsd, dv, dvcp, dvhd
    • i420, i422, yv16, hfyu
  • Raw DV
    • PAL / NTSC dvsd

Important: Veejay can only deal with video files that consists entirely out of whole images, only I-frames.

You can also load mime type image/jpeg images ( .jpg, .jpeg, .JPG, .JPEG)

so... Which codec to use ?

MotionJPEG (mjpeg) is the veejay codec of choice for most applications, it gives you a good tradeof between compression, quality and compatibility. M-JPEG is an intraframe-only compression, each video frame is coded separately as a JPEG image, giving advantage of rapidly changing motion in the video stream.

If you ever want more speed, use AVI yv16 or i420 before recording to new samples :

  • using console client and sayVIMS (selector 302 Set codec to use for recording (use 'x' to see list))
  • from gui client reloaded [Sample/Stream panel] ---> [Recording to Disk panel] ---> [Codec drop down list].

Floss tools that support MJPEG:

  • Cinelerra - Video editing and compositing software
  • Kdenlive - Video editing software
  • Shotcut - Video editing software
  • MJPEG Tools - Set of tools for videos recording and playback
  • Mplayer, and mencoder - Movie player which runs on many systems
  • FFmpeg - Vast suite of libraries and programs for handling video, audio, and other multimedia files and streams
  • Libav - FFmpeg fork, has a second choice
  • VLC - Media player, streaming media server and more...
  • Lives - VJ and Video Editing system
  • Kino (not been actively maintained since 2009)
  • Linux Video Studio (not actively maintained)

Which resolutions to use ?

Veejay can do:

  • high resolutions aka HDTV
  • pal 16/9 : 1024x576
  • pal: 720x576
  • ntsc: 720x480
  • 1/4 pal: 360x288
  • 1/4 ntsc: 360x240

In fact pretty much any resolution divisible by 8, which is a limitation for some video internals (encoders and effects). Finally it is an everyone finding balance between preciseness of graphics, complexity of effect's chain and necessary resources for a realtime accuracy.

If you load multiple video files on the command line, make sure that all files have the same resolution and audio properties.

How to convert ?

You can use FFMpeg

$ ffmpeg -i input-file -c:v mjpeg -pix_fmt yuvj422p -q:v 1 -an output-file.avi

Your input video input-file will be transcode to mjpeg video codec, with a pixel format yuvj422p - color values from 0-255 and only horizontal chroma resolution is halved. For better performance (but less image accuracy...) you can choose yuvj420p , in that case, both horizontal and vertical chroma resolution are halved. Finally it use a video quantifier of 1 setting the quality scale (VBR) to best image quality.

In previous example, audio is muted using the -an flag, consequently you would start veejay with -a0 to disable audio.

Optionally add PCM WAVE 16bit audio, 48.0 Khz, 2 channels, 8 bits per channel, HD resolution and 25 frames per second.

$ ffmpeg -i input-file -q:v 1 -c:v mjpeg -s 720p -r 25 -pix_fmt yuvj422p -acodec pcm_s16le -ar 48000 -ac 2 output-file.avi

For more detailled informations concerning audio, look at README.audio.md

Check FFmpeg documentation for detailed description of transcoding process and possible customization/automation.

Or, you can use mplayer

$ mencoder -ovc lavc -oac pcm -lavcopts vcodec=mjpeg -o <outputfile> <inputfile>

To scale on the fly, use

$ mencoder -ovc lavc -oac pcm -lavcopts vcodec=mjpeg -vf scale=352:288 -o <outputfile> <inputfile>

Bulk encoding

A quick hint for bulk encoding a bunch of capture.dv files

$ for i in `ls *dv`;do mencoder -ovc lavc -oac pcm -lavcopts vcodec=mjpeg -o `echo $i | sed s/.dv/.avi/` $i; done;

Consult mplayer documentation about other options, such as cropping and filtering out blocks in video.

Going deeper in videos

What is Dummy mode ?

$ veejay -d

Dummy mode opens up a 'color stream' to start veejay without a video file.

If you use a video file, veejay will take that file's properties as default settings for the whole session.

Virtual video device

You can create a fake v4l2 device (/dev/videoX), using v42loopback.

Setup a single virtual video device on /dev/video0 (assuming that it does not previously exist), stream some screen capture to it and open veejay using this source (audio disabled)

# modprobe v4l2loopback
$ ffmpeg -f x11grab -r 25 -s 720x576 -i :0.0+5,10 -vcodec rawvideo -pix_fmt yuv422p -f v4l2 /dev/video0
$ veejay -A1 -a0

Here, 0.0 is display.screen number of your X11 server, same as the DISPLAY environment variable and 5 is the x-offset and 10 the y-offset for the grabbing.