我正在做一个创建照相亭的项目。我有一台相机（佳能 550d）和一台显示我写的网页的触摸屏电脑（运行 ubuntu）。
我正在使用gphoto2从网页中控制我的 DSLR exec()，我可以轻松拍照。
我的问题是我还想在人们拍照之前显示相机的实时预览。现在，我准备好了一个脚本，它在一个无边界窗口中打开一个 MPlayer 实例，该窗口也位于所有内容之上，代码在一个名为的文件中live.sh：
#!/bin/bash
gphoto2 --capture-movie --stdout > fifo.mjpg & mplayer -cache 32 -demuxer 35 -noborder -geometry 50%:100 -ontop 1 fifo.mjpg
基本上 gphoto2 流到 fifo.mjpg 然后 MPlayer 播放该文件。
当我从终端运行它时，一切都很好：
bash live.sh
如果我从 php 中运行相同的命令，它不起作用
exec("bash live.sh", $output);
看看我从这两个环境运行时得到的输出
从终端运行（此工作）：
MPlayer 1.2.1 (Debian), built with gcc-5.3.1 (C) 2000-2016 MPlayer Team
mplayer: could not connect to socket
mplayer: No such file or directory
Failed to open LIRC support. You will not be able to use your remote control.
Playing 1.
File not found: '1'
Failed to open 1.
Playing fifo.mjpg.
libavformat version 56.40.101 (external)
Capturing preview frames as movie to 'stdout'. Press Ctrl-C to abort.
*** Error ***
An error occurred in the io-library ('Could not claim the USB device'): Could not claim interface 0 (Device or resource busy). Make sure no other program (gvfs-gphoto2-volume-monitor) or kernel module (such as sdc2xx, stv680, spca50x) is using the device and you have read/write access to the device.
ERROR: Movie capture error... Exiting.
Movie capture finished (0 frames)
libavformat file format detected.
Cannot seek backward in linear streams!
Seek failed
[mjpeg @ 0x7f9cffecb540]Found EOI before any SOF, ignoring
[mjpeg @ 0x7f9cffecb540]Changeing bps to 8
[lavf] stream 0: video (mjpeg), -vid 0
VIDEO: [MJPG] 1056x704 0bpp 25.000 fps 0.0 kbps ( 0.0 kbyte/s)
Load subtitles in ./
Failed to open VDPAU backend libvdpau_va_gl.so: cannot open shared object file: No such file or directory
[vdpau] Error when calling vdp_device_create_x11: 1
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
libavcodec version 56.60.100 (external)
Selected video codec: [ffmjpeg] vfm: ffmpeg (FFmpeg MJPEG)
==========================================================================
Audio: no sound
Starting playback...
[mjpeg @ 0x7f9cffecb540]Found EOI before any SOF, ignoring
[mjpeg @ 0x7f9cffecb540]Changeing bps to 8
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
Movie-Aspect is undefined - no prescaling applied.
[swscaler @ 0x7f9d00c36fa0]bicubic scaler, from yuv422p to yuyv422 using MMXEXT
[swscaler @ 0x7f9d00c36fa0]using unscaled yuv422p -> yuyv422 special converter
VO: [xv] 1056x704 => 1056x704 Packed YUY2
Movie-Aspect is undefined - no prescaling applied.
VO: [xv] 1056x704 => 1056x704 Packed YUY2
V: 0.5 0/ 0 37% 14% 0.0% 0 0 50%
MPlayer interrupted by signal 2 in module: enable_cache
MPlayer interrupted by signal 2 in module: video_read_frame
[mjpeg @ 0x7f9cffecb540]overread 8
[mjpeg @ 0x7f9cffecb540]EOI missing, emulating
V: 0.6 0/ 0 36% 13% 0.0% 0 0 50%
Exiting... (Quit)
尽管存在所有错误，但一切都运行得非常好。
这是我从 PHP 中的 exec() 运行时得到的输出（这不起作用）：
array(16) {
[0]=>
string(71) "MPlayer 1.2.1 (Debian), built with gcc-5.3.1 (C) 2000-2016 MPlayer Team"
[1]=>
string(39) "Terminal type `unknown' is not defined."
[2]=>
string(0) ""
[3]=>
string(10) "Playing 1."
[4]=>
string(0) ""
[5]=>
string(0) ""
[6]=>
string(18) "Playing fifo.mjpg."
[7]=>
string(29) "
Cache fill: 0.00% (0 bytes)"
[8]=>
string(0) ""
[9]=>
string(40) "libavformat version 56.40.101 (external)"
[10]=>
string(33) "libavformat file format detected."
[11]=>
string(39) "Cannot seek backward in linear streams!"
[12]=>
string(42) "[mjpeg @ 0x7fb771bec540]Changeing bps to 8"
[13]=>
string(38) "[lavf] stream 0: video (mjpeg), -vid 0"
[14]=>
string(69) "VIDEO: [MJPG] 1056x704 0bpp 25.000 fps 0.0 kbps ( 0.0 kbyte/s)"
[15]=>
string(20) "Load subtitles in ./"
}
如果有人对如何使这项工作有任何想法，我将不胜感激。
谢谢！