Recording and Playback

You can export video sent from UltraGrid by passing '--record' parameter:

uv -t deltacast --record

Optionally you can specify also output directory:

uv -t deltacast --record lecture-20130424

Such video, you can latter send to a remote location:

uv --playback lecture-20130424 <remote_host>

Note: In older UltraGrid versions the parameters were called --export/--import.

Converting exported video

Also, you can process saved images, depending on its compression.

YUV

You can process uncompressed YUV frames like that:

ls | grep '\.yuv$' | sed 's/\.yuv$//' | parallel mv {}.yuv {}.Y  # files need to have .Y extension 

ffmpeg -pix_fmt uyvy422 -s 1920x1080 -i %08d.Y -codec:v huffyuv out.avi

(you can use also "for n in *yuv; do mv $n ${n/yuv/Y}; done" instead of parallel, however you are limited by maximal lenght of command-line arguments, which will however limit the amount of files that can be processed, then)

H.264/HEVC

H.264 or HEVC pictures can be simply concatenated by running:

cat *.h264 > out.h264

or if there are more files (than maximal argument list size), you can use:

:>| out.h264

ls [0123456789]*.h264 | xargs -n 1 sh -c 'cat "$0" >> out.h264'

Then you may convert video to more convenient file format, eg:

ffmpeg -r 30000/1001 -i out.h264 -i sound.wav -codec:v copy -codec:a aac -strict -2 -r 30000/1001 output.mp4

In this example:

• we are providing explicitly input frame rate (29.97). Otherwise, ffmpeg would guess from the file and since there are no headers, only frame timestamps, it might be incorrect.
• we are adding the sound recorded by UltraGrid, it is reencoded from PCM to AAC, option "-strict -2" is there because AAC support in FFMPEG is considered experimental
• output frame rate is there just for sure, it can be omitted

JPEG

And for JPEG, you may use:

mencoder "mf://*.jpg" -mf fps=25 -o output.avi -ovc copy

or (transcoding to H.264, single pass)

mencoder mf://*jpg -audiofile sound.wav -oac copy -ovc x264 -o out.avi -of lavf  -x264encopts bitrate=10000:tff

or (transcoding to H.264, two pass, very high quality)

mencoder mf://*jpg -ovc x264 -x264encopts pass=1:preset=veryslow:bitrate=20000:tff -o /dev/null

mencoder mf://*jpg -audiofile sound.wav -oac copy -ovc x264 -x264encopts pass=2:preset=veryslow:bitrate=20000:tff -o out.avi

Converting for UltraGrid

RGB

Note: RGB uncompressed video will consume significant amount of storage and you will need to have hi-bandwidth storage (aka SSD) to play it back. If it is not the case, consider storing the record as JPEG.

Convert video to sequence of video frames:

mplayer -vo pnm <video>

Drop PNM headers:

ls | grep '\.ppm$' | sed 's/\.ppm$//' | parallel -q bash -c 'tail {}.ppm -n +4 > {}.rgb'

Finally, create video.info (in same folder) with following content (change size,fps and count):

 version 1
 width 320
 height 240
 fourcc RGB2
 fps 24.00
 interlacing 0
 count 1000

MJPEG

You can also create JPEG files instead to RGB to reduce required disk space. The process is even easier than in previous case - just convert the video into sequence of video images:

mplayer -vo jpeg <video>

And, subsequently, add correct metadata file (called video.info in same directory):

 version 1
 width 320
 height 240
 fourcc MJPG
 fps 24.00
 interlacing 0
 count 1000

Now you should be able to play image sequence by executing:

 uv --playback <directory_with_JPEG_images>

Converting audio for UltraGrid

Recorded audio is stored in the same directory alongside the video files. It needs to be in uncompressed PCM format (signed, little-endian). However, you can convert it quite easily to UG format:

 sox <source> -e signed -b 16 sound.wav

or you can use FFMPEG (eg. if the source is a multimedia conatiner):

ffmpeg -i <source> -acodec pcm_s16le -ar 48000 -ac 2 sound.wav

Direct playback with V4L2 and ALSA (Linux only)

You can also directly playback a multimedia file through v4l2loopback device. Just add a module (it may be needed to compile for you kernel first):

modprobe v4l2loopback

Then new device /dev/videoX appears (further assuming that device index is 2). This device can be written eg. with:

ffmpeg -re -i video.mp4 -f v4l2 /dev/video2

For more advanced setups please refer here and here.

Then you should be able to grab from that V4L2 device in UltraGrid as usual:

uv -t v4l2:device=/dev/video2 <receiver>

Audio

Similarly you may also add audio with ALSA loopback device:

modprobe snd_aloop

Then you can play the media combined through audio and video loopback:

ffmpeg -re -i media.mp4 -f v4l2 /dev/video2 -f alsa hw:CARD=Loopback,DEV=0

and UltraGrid capture will be:

uv -t v4l2:device=/dev/video2 -s alsa:hw:CARD=Loopback,DEV=1 <receiver>

Note: Please note different ALSA device indices in ffmpeg and uv commands (DEV=0 and DEV=1).

Of course audio can be also played without the video.