diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/misc/rawout.txt | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/doc/misc/rawout.txt b/doc/misc/rawout.txt new file mode 100644 index 0000000..240ede3 --- /dev/null +++ b/doc/misc/rawout.txt @@ -0,0 +1,134 @@ +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 |