[PD-cvs] externals/pdp/doc/misc rawout.txt,NONE,1.1

[Tom Schouten]

Update of /cvsroot/pure-data/externals/pdp/doc/misc
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv23292/doc/misc

Added Files:
	rawout.txt 
Log Message:
pdp: missing files

--- NEW FILE: rawout.txt ---
How to use [pdp_rawout] to record video
---------------------------------------

Some observations
* pdp is a real time performance tool
* ffmpeg and mencoder are very nice pieces of software that
  solve the video encoding problem
* encoding video is cpu intensive
* large harddisks are cheap

For these reason, I decide to not implement container/codec
recording in pdp. Using [pdp_rawout] and [pdp_rawout~] it is
possible to dump video and audio streams directly to harddisk
using the minimal amount of cpu time. There they can be picked
up later by tools like mencoder and ffmpeg.

( For playback, pdp supports only libquicktime, which is, next
to mjpegtools, a good solution for frame-based seekable video
files. Since version 0.9.4 libquicktime supposedly supports AVI
playback and record. Streaming playback and more efficient block 
codecs can be supported externally using [pdp_rawin] )

FFMPEG
------

FFMPEG is the 'industry standard' for open source video encoding.
Its core components are libavcodec and libavformat, which implement
the coder/decoder and container format handling. The latter two
are used in a lot of other projects, like MPlayer and libquicktime.

Send a video stream through [pdp_convert bitmap/i420/*]
then stream it to disk using [pdp_rawout /tmp/video.i420] while
you are performing. You can convert it to divx avi using

ffmpeg -an -r 25 -s 320x240 -f rawvideo -i video.i420 video.avi

To include audio, use [pdp_rawout~ 2 /tmp/audio.s16] to stream
audio to disk. You can convert it with ffmpeg using

ffmpeg -ar 44100 -ac 2 -f s16le -i audio.s16 audio.mp3


Doing both at the same time:

ffmpeg -r 25 -s 320x240 -f rawvideo -i video.i420 -ar 44100 -ac 2 -f s16le -i audio.s16 -vcodec mjpeg -b 3000 clip.avi

Note: i didn't figure out how to make ffmpeg read yv12 encoded files. However,
pdp supports the bitmap/i420/* format. The latter is also the data format used in
the yuv4mpeg protocol from the mjpeg tools.


Codecs and Bitrates
-------------------

The preferred codec to use during the editing stage is motion JPEG. If
you have the space, use raw files, but i haven't figured out how to make
them portable. The most portable mjpeg format seems to be wrapped in a mov.
This is the format used in cinelerra.

Uncompressed 320x240x25 yv12/i420 is 2.88 mbyte/sec
A decent mjpeg compresion rate is 4:1, giving 720 kbyte/sec = 5760 kbit/sec
with practically no loss of quality. 3000 and 2000 kbps are still acceptable.

Sometimes it might be interesting to create DV files. These have a tighter
binding to TV norms PAL and NTSC, and seem to be a standard at this moment.
DV gives about 13gig/hour or 3 mbyte/sec. The actual rate is 5:1 compression
at 25 Mbps (video only). Adding audio, timecode, etc.. comes to about 29 Mbps.
(TODO: how to create DV files)

The preferred distribution codec is either DIVX or H.264 (don't confuse
with H.263 which is aimed at low bitrate video conferencing)


A/V sync
--------

The key to A/V sync is the observation that the ratio between audio and
video frequency (samplerate and framerate), is a _rational_ one. This enables
to have perfect sync: there are no roundoff errors since the relation between
audio and video sample times can be computed exactly. 
The object [pdp_metro~] can be used to produce a locked video clock, given a 
rational framerate. It can produce a video clock that is compatible with 
standard A/V rates. 
For example the awkward 29.97Hz video rate is exactly supported as 29970/1000. 
Note that the 44.1kHz audio rate does not yield simple fractions for standard 
NTSC and PAL/SECAM framerates. I.e. in DV you have to use 48kHz. Enabling 
arbitrary long buffering (bufsize -1) in [pdp_rawout] and using [pdp_metro~] 
with the correct sample rate and video frame rate should produce perfect A/V 
sync without dropouts if your harddisk can keep up on the average.


MJPEGTOOLS
----------

I mainly use lavtrans for converting the avi/mjpeg file made with ffmpeg
to quicktime format. This should be readable by most video editing software.
I had some problems with sharing th avi/mjpeg files themselves. To convert
the avi file to mov use:

lavtrans -o clip.mov -f q clip.avi



Mplayer/Mencoder
----------------

The MPlayer project uses libavcodec, and even distributes a copy with the MPlayer source.
You'll need mencoder mainly if you want to use an encoder that's not in the
ffmpeg package (lavcodec), or what to do some format conversion that's not
supported by ffmpeg directly. Of course mplayer is handy for inspecting raw files.
To play a raw video stream try:

mplayer -rawvideo on:w=320:h=240:fps=25 video.i420

To encode video only using the ffmpeg (lavc) mjpeg codec
(it is possible to use yv12 here, using the format=yv12 option)

mencoder -rawvideo on:w=320:h=240:fps=25 video.i420 -ovc lavc -lavcopts vcodec=mjpeg -o clip.avi





links
-----
http://mjpeg.sourceforge.net/
http://ffmpeg.sourceforge.net/index.php
http://libquicktime.sourceforge.net/
http://www.mplayerhq.hu
http://libdv.sourceforge.net/
http://solarmuri.ssl.berkeley.edu/~fisher/public/manuscripts/scientific-movie-HOWTO.txt
http://mpeg4ip.sourceforge.net/
http://heroinewarrior.com/cinelerra.php3
http://www.adamwilt.com/DV-tech.html