在Linux下播放与录制电视

最近，在自己的Debian 7.2 64位系统上成功安装了圆刚AverMedia C725B视频卡驱动。于是，可以使用mplayer与mencoder来看电视与录节目了。其中，用于播放电视的命令如下：

mplayer tv:// -tv driver=v4l2:device=/dev/video0:norm=PAL:alsa:adevice=hw.2,0:amode=1:audiorate=48000:forceaudio:volume=100:immediatemode=0:normid=8:input=1:buffersize=1024:width=768:height=576:outfmt=i420 -vo xv -ao sdl -aspect 4:3

但该命令存在的问题时，当电视播放一段时间后视频与音频便不再同步。

录制节目则可以用mencoder来实现：

mencoder tv:// -tv driver=v4l2:device=/dev/video0:norm=PAL:alsa:adevice=hw.2,0:amode=1:audiorate=48000:forceaudio:volume=100:immediatemode=0:normid=8:input=1:buffersize=64:width=720:outfmt=yuy2
-oac mp3lame -lameopts fast:preset=standard -ovc lavc -lavcopts vcodec=mpeg4:vhq:vbitrate=1800 -o output.avi

上面两条命令虽然能用，但却无法实现电视节目的边放边录。通过网上的搜索（参考）和自己的测试，电视的录制与同时播放可以采用命名管道+tee+mplayer来实现。为了方便操作，写了一个脚本程序rtv，其可用三种模式运行：

• watch：在播放电视的同时，将其存为avi文件。
• nowatch：只录制节目不用mplayer播放。
• onlywatch：只用mplayer看节目而不录制。

脚本首先检测用户的命令行参数输入，然后查看是否已有mencoder、tee、mplayer进程运行。若存在，则不再执行后面的部分；否则，执行如下的流程：

1. 首先，使用mkfifo创建命名管道；
2. 其次，用tee命令读取管道：在录制与播放的模式下（watch）将其分为两路，一路送至avi文件，一种送至mplayer用于播放；在只录制不播放的模式下（nowatch），只输出至avi文件；在纯播放模式下（onlywatch），只送至mplayer。
3. 最后，用mencoder从/dev/video0截取视频流并输出到之前创建的命名管道。

rtv脚本内容如下：

#!/bin/bash 

# Define a function for returning a process id
function get_pid_by_name()
{
    local process_str 

    echo "Searching process $1..."
    process_str=`ps aux | grep "$1" | tr --squeeze-repeats ‘[:blank:]+‘ ‘\t‘ | cut -f 2`
    if [ -n "$process_str" ]; then
        # The process for grep appears in the second field
        process_str=`echo $process_str | cut -s -d ‘ ‘ -f 1`
        if [ -n "$process_str" ]; then
            temp_pid=$process_str
            echo "The process id is $temp_pid!"
        else
            echo "The process $1 cannot be found, perfect!"
        fi
    else
        echo "The process $1 cannot be found, perfect!"
    fi
} 

if [ -z "$1" ]; then
    echo "Please specify the recording and watching mode: watch|nowatch|onlywatch"
    exit 0
fi 

if [ "$1" != "onlywatch" ] && [ -z "$2" ]; then
    echo "Please provide the video file name to be saved!"
    exit 0
fi 

# Declare the pid as integers
declare -i temp_pid=-1 mplayer_pid=-1 mencoder_pid=-1 tee_pid=-1 

get_pid_by_name mencoder
mencoder_pid=$temp_pid
temp_pid=-1 

get_pid_by_name tee
tee_pid=$temp_pid
temp_pid=-1 

get_pid_by_name mplayer
mplayer_pid=$temp_pid
temp_pid=-1 

if [ $(($mencoder_pid!=-1 && $mplayer_pid!=-1 && $tee_pid!=-1)) = 1 ]; then
    echo "A tv recording or watching activity is now working, please exit it first!"
    exit 0
fi 

# Create FIFO named pipe
if [ ! -e "/tmp/tv.fifo" ]; then
    echo "FIFO does not exist, now being created..."
    mkfifo /tmp/tv.fifo && echo "Creating FIFO successful!"
fi 

# Start tee and mplayer
case "$1" in
    watch ) echo "Start recording tv and watch it using mplayer..."
            # Note: sudo must be used in order to make mplayer appear
            cat /tmp/tv.fifo | tee -a "${2%.avi}.avi" | sudo -u orlando DISPLAY=:0.0 mplayer -cache 5120 -ao sdl -vo xv - & ;;
    nowatch ) echo "Start recording tv without watching it..."
              cat /tmp/tv.fifo | tee -a "${2%.avi}.avi" & ;;
    onlywatch ) echo "Start watching tv without recording it..."
                # Note: "tee -a -" will not work here
                # Cache size should not be too large and 1024 kB is a reasonable value, otherwise, the response when changing the channel will be too slow
                cat /tmp/tv.fifo | tee | sudo -u orlando DISPLAY=:0.0 mplayer -cache 1024 -ao sdl -vo xv - & ;;
    * ) echo "Please specify the recording and watching mode: watch|nowatch|onlywatch"
        exit 0;
esac 

# Start mencoder to feed the video stream into FIFO
echo "Now start mencoder to capture tv..."
mencoder tv:// -tv driver=v4l2:device=/dev/video0:norm=PAL:alsa:adevice=hw.2,0:amode=1:audiorate=48000:forceaudio:volume=100:immediatemode=0:normid=8:input=1:buffersize=1024:width=768:height=576:outfmt=i420 -oac mp3lame -lameopts fast:preset=standard -ovc lavc -lavcopts vcodec=mpeg4:vhq:vbitrate=1800 -o /tmp/tv.fifo

停止录制与播放电视的脚本stop_rtv为：

#!/bin/bash 

# Define a function for returning a process id
function get_pid_by_name()
{
    local process_str 

    echo "Searching process $1..."
    process_str=`ps aux | grep "$1" | tr --squeeze-repeats ‘[:blank:]+‘ ‘\t‘ | cut -f 2`
    if [ -n "$process_str" ]; then
        # The process for grep appears in the second field
        process_str=`echo $process_str | cut -s -d ‘ ‘ -f 1`
        if [ -n "$process_str" ]; then
            temp_pid=$process_str
            echo "The process id is $temp_pid!"
        else
            echo "The process $1 cannot be found, perfect!"
        fi
    else
        echo "The process $1 cannot be found, perfect!"
    fi
} 

# Declare pid as integers
declare -i temp_pid=-1 mplayer_pid=-1 mencoder_pid=-1 tee_pid=-1 

# Kill mencoder process
get_pid_by_name mencoder
mencoder_pid=$temp_pid
temp_pid=-1 

if [ $(($mencoder_pid!=-1)) = 1 ]; then
   # The SIGINT has no effect on mencoder processes while SIGKILL will cause loss of /dev/video0 node
   kill -2 $mencoder_pid && echo "mencoder has been killed!"
else
   echo "mencoder process does not exist!"
fi 

# Kill tee process
get_pid_by_name tee
tee_pid=$temp_pid
temp_pid=-1 

if [ $(($tee_pid!=-1)) = 1 ]; then
   kill -2 $tee_pid && echo "tee has been killed!"
else
   echo "tee process does not exist!"
fi 

# Kill mplayer process if not in nowatch mode
if [ "$1" != "nowatch" ]; then
   get_pid_by_name mplayer
   mplayer_pid=$temp_pid
   temp_pid=-1 

   if [ $(($mplayer_pid!=-1)) = 1 ]; then
      # Note: mplayer is started by using sudo, therefore when killing it, sudo should also be used
      sudo -u orlando kill -2 $mplayer_pid && echo "mplayer has been killed!"
   else
      echo "mplayer process does not exist!"
   fi
fi 

echo "TV recording and playing have been stopped!"

将上面的两个脚本与at命令结合，则可以实现定时录制与播放节目了。例如：

$ at 20:00 today
warning: commands will be executed using /bin/sh
at> rtv watch 我爱发明
at> <EOT>                        # Input Ctrl+D
job 21 at Wed Feb    5 20:00:00 2014
$ at 21:00 today
warning: commands will be executed using /bin/sh
at> stop_rtv watch
at> <EOT>                        # Input Ctrl+D
job 22 at Wed Feb    5 21:00:00 2014

由于晚上播出的电视节目大部分在第二天白天会重播，因此在自己上班的同时，这些节目便可以按计划一个不落地录下来。同时，原本需要晚上熬夜看的节目也可以保存起来等到第二天再看。

14年6月15日 与此同时，为了方便播放与停止播放，在~/.bashrc中定义了如下aliases：

alias ptv="mplayer -forceidx"
alias tv="rtv onlywatch"
alias stop_tv="stop_rtv onlywatch"

其中，ptv在调用mplayer时使用-foceidx选项强制生成index信息，从而可以在播放的时候快进或者是快退。这是由于从视频卡直接采集生成的avi文件默认没有index信息（奇怪的是甚至即便是用mplayer生成了idx文件，用其他的播放器也没有办法播放）。不过，只使用-forceidx并不会将index信息保存下来，因此，下一次再次播放的时候，还需要重新生成index，比较耗时间。为此，编写gen_idx与ptv_idx两个脚本程序。前者用于生成并保存index信息，后者用于在启动播放时加载已经生成的index文件。两个程序的内容如下：

gen_idx:

#!/bin/bash

mplayer -forceidx -saveidx "`basename \"$1\" \".avi\"`".idx "$1"

ptv_idx:

#!/bin/bash

mplayer -loadidx "`basename \"$1\" \".avi\"`".idx "$1"

下面的脚本程序tv_nomen，则直接使用mplayer播放视频，而不经过mencoder的中转。这也是目前看电视直播的方法。采用该方法原本的想法是能够解决电视播放一断时间后，视频变得迟缓，开始与声音不同步的问题。但事实证明该问题并不能通过直接使用mplayer播放来解决。似乎这个问题是由于系统性能不高导致的。

#!/bin/bash

# Play the tv using only mplayer: when a long time is elapsed, audio and video will be asynchronous using this method
sudo -u orlando DISPLAY=:0.0 mplayer tv:// -tv driver=v4l2:device=/dev/video0:norm=PAL:alsa:adevice=hw.2,0:amode=1:audiorate=48000:forceaudio:volume=100:immediatemode=0:normid=8:input=1:buffersize=1024:width=768:height=576:outfmt=i420 -vo xv -ao sdl -aspect 4:3 -nocache -framedrop

在Linux下播放与录制电视