lavrec.1

Motion JPEG编解码器源代码

.TH "lavrec" "1" "27 August 2003" "MJPEG Linux Square" "MJPEG tools manual"

.SH NAME
lavrec \- Record MJPEG-video from a zoran/video4linux-device

.SH SYNOPSIS
.B lavrec
.RI [ options ]
.IR filename(s)

.SH DESCRIPTION
\fBlavrec\fP can be used to record video in MJPEG format (either
quicktime or AVI) from a zoran video-capture device, such as
the Miro/Pinnacle DC10(+), the Iomega Buz or Linux Media Labs' LML33,
or from a generic video4linux device, such as the cheap Bt848 or Bt878
based TV-cards that are being sold in every computer shop around the
corner.


.SH OPTIONS
\fBlavrec\fP accepts the following options:

.TP 8
.B filename
The file to record to (*.avi, *.qt). Use a % to record
to multiple files (using file%02d.avi will record to file00.avi,
file01.avi, etc). You can also give more than one filename, which
will have the same effect. This will avoid problems resulting
from filetype or filesystem size limits. AVI, for example, has a
2 GB limit, as does ext2fs in 2.2.x kernels.

.TP 8
.BR \-\-software\-encoding
By default, lavrec will capture in a mode that is only suitable
for recording from hardware MJPEG devices. Using this option
will make lavrec use software\-JPEG\-encoding (using libjpeg)
which enables MJPEG\-video\-capture from many generic video4linux
devices (such as Bt848/Bt878\-based ones).

.TP 8
.BR \-f/\-\-format " [" a | A | q | m ]
The format in which the video should be saved to the harddisk.
  a - MJPEG AVI
  A - MJPEG AVI with fields exchanged
  q - Quicktime
.br
By default, lavrec will look at the extension of the first file
(*.avi, *.qt) and choose a format based on that.

.TP 8
.BR \-i/\-\-input " [" p | P | n | N | s | S | t | T | f | a ]
The recording source and the video source standard format.
 p - PAL through Composite or 1st Bt8x8 input
 P - PAL through SVHS- or 2nd Bt8x8 input
 t - PAL through TV-tuner- or 3rd Bt8x8 input
 n - NTSC through Composite or 1st Bt8x8 input
 N - NTSC through SVHS- or 2nd Bt8x8 input
 T - NTSC through TV-tuner- or 3rd Bt8x8 input
 s - SECAM through Composite or 1st Bt8x8 input
 S - SECAM through SVHS- or 2nd Bt8x8 input
 f - SECAM through TV-tuner- or 3rd Bt8x8 input
 a - (or every other letter) Autosense (default)

.TP 8
.BI  \-d/\-\-decimation " num"
Recording decimation, either 1, 2 or 4. This will decimate the size
of the recorded video horizontally and vertically. To use different
horizontal and vertical decimations, use two numbers, the first one
being the horizontal and the second one being the vertical (-d 12).
\fBNote:\fP this option can only be used during hardware recording.

.TP 8
.BI \-g/\-\-geometry " WxH(+X+Y)"
\fBFor hardware recording:\fP An X\-style geometry string, giving
the geometry of the undecimated subframe to record. The default is the
full frame, so 720x576/480+0+0 for Buz/LML33\-users and 640x480+0+0
or 768x576+0+0 for DC10(+)-users.
\fBFor software recording:\fP The size of the video to be captured.
Currently, width and height need to be a multiple of 16. You always
capture the full frame since most video4linux devices don\'t support
subframe capture.

.TP 8
.BI \-q/\-\-quality " num"
Quality of the JPEG\-video to be recorded (in percent). This must be a
number between 0 and 100. Lower quality should generally mean lower
filesize, higher quality will take more diskspace but will give more
detailed perfectness in the resulting recorded video. Default is 50%.

.TP 8
.BI \-C/\-\-channel " LIST:CHAN"
Choose the channel to record from (xawtv-style). By default, lavrec will
just use the current TV channel.

.TP 8
.BI \-t/\-\-time " num"
Recording time in seconds. The default is unlimited. To stop capturing
video while recording, use Ctrl-C.

.TP 8
.B \-S/\-\-single\-frame
Single-frame capture mode. This means that one can capture individual
frames from the capture device.

.TP 8
.BI \-T/\-\-time\-lapse " num"
time-lapse factor, which means that only every <num>th frame is saved
to the recording file.

.TP 8
.B \-w/\-\-wait
If this option is given, lavrec will wait for the user to press enter
before starting to record.

.TP 8
.B \-B/\-\-batch
This option turns off all possible interactivity options and limits
console output as much as possible. Useful for cron/scheduled recordings.

.TP 8
.BI \-a/\-\-audio\-bitsize " num"
Audio size in bits, either 0, 8 or 16 (default). 0 means no audio.
.TP 8

.BI \-r/\-\-audio\-bitrate " num"
Audio sampling rate in Hz. This must be a sampling rate which is
supported by the soundcard. Often-supported audio sampling rate values
are 11025, 22050 or 44100 (default).

.TP 8
.B  \-s/\-\-stereo
Capture in stereo. By default, lavrec captures in mono.
.TP 8

.BI \-l/\-\-audio\-volume " num"
Recording level. This must be a value between 0 (no sound) and 100
(loud recording). \-1 (default) means to not touch the mixer settings
at all.

.TP 8
.B \-m/\-\-mute
Mute sound output while recording. This can be useful when recording
sound from the microphone to disable echos. This option is disabled by
default.

.TP 8
.BR \-R/\-\-audio\-source " [" l | m | c ]
Recording source, either (l)ine-in, (m)icrophone or (c)d-rom. The default
is to record from line-in (l).

.TP 8
.BR \-U/\-\-use\-read
Use the read() system call rather than the mmap() system call for
audio recording. This may fix many audio recording problems.

.TP 8
.BR \-c/\-\-synchronization " [" 0 | 1 | 2 ]
Audio/video synchronization level efforts. (0) means no synchronization,
(1) means that lavrec will replicate frames for lost frames. (2) means
that lavrec will replicate frames for lost frames and do sync correction.
Default is 2.

.TP 8
.BI \-n/\-\-mjpeg-buffers " num"
Number of MJPEG-buffers. Default is 32. Try changing this number if you
have many lost frames.

.TP 8
.BI \-b/\-\-mjpeg-buffer-size " num"
MJPEG buffersize in kilobytes. The default is 256 kB.

.TP 8
.BI \-\-max\-file\-size " num"
The maximum file size per JPEG file. By default, lavrec uses the maximum
possible size for that specific recording format.

.TP 8
.BI \-\-max\-file\-frames " num"
The maximum number of frames per per JPEG file. By default, the number of
frames is only limited by other factors, such as maximum file size.

.TP 8
.BI \-\-file\-flush " num"
Flush the file to disk after every num frames captured.

.TP 8
.BI \-v/\-\-verbose " num"
Verbosity level (0, 1 or 2). Default is 0.

.SH ENVIRONMENT
The following environment variables can be recognized by lavrec:
.TP 8
.B LAV_VIDEO_DEV
The video device. Default is /dev/video
.TP 8
.B LAV_AUDIO_DEV
The audio device. Default is /dev/dsp
.TP 8
.B LAV_MIXER_DEV
The mixer device. Default is /dev/mixer

.SH OUTPUT
Lavrec will output the current recording state. Typically, this looks like:
.br
0.06.14:22 int: 00040 lst:0 ins:0 del:0 ae:0 td1=0.014 td2=0.029
.br
The first part is the time that has been spent recording (hours \- minutes \-
seconds \- frames). 
.B int
is the interval (in milliseconds) between two captured frames (this should
be around 40 for PAL/SECAM and 33 for NTSC).
.B lst
is the number of lost frames.
.B ins
and
.B del
are the number of frames inserted and deleted for sync correction.
.B ae
is the number of audio errors.
.B td1
and
.B td2
are the audio/video time-difference (out\-of\-sync'ness).

.SH TYPICAL RECORDING SESSIONS
Okay, that's a lot of options. Now how would I normally record video?
Let's assume you want to record at VCD resolution (352x288) from PAL source.
You might want some higher quality than default (80%). You use default
audio options and record to an AVI file. That having said, your recording
command line would look like:
.TP 8
.B From hardware MJPEG devices (S\-video input)
lavrec --format=a --input=P --quality=80 --decimation=2 /path/to/file.avi
.TP 8
.B From normal video4linux devices
lavrec --software-encoding --format=a --input=p --quality=80 --geometry=352x288 /path/to/file.avi

.SH BUGS
lavrec should be able to detect automatically whether to use software
JPEG encoding or whether to use the card's hardware JPEG encoding
features (if available).

Besides that, software JPEG encoding seems, for some people, to cause
small out-of-sync'ness. SMP support for JPEG encoding is currently
work-in-progress.

.SH AUTHOR
This man page was written by Ronald Bultje.
.br
If you have questions, remarks, problems or you just want to contact
the developers, the main mailing list for the MJPEG\-tools is:
.br
    \fImjpeg\[e-mail]\fP
.br
.br
For more info, see our website at
.br
    \fIhttp://mjpeg.sourceforge.net/\fP

.SH SEE ALSO
.BR mjpegtools (1),
.BR lavplay (1)