一键生成 Android 录屏 gif 的脚本

宁可枝头抱香死，何曾吹落北风中。这篇文章主要讲述一键生成 Android 录屏 gif 的脚本相关的知识，希望能为你提供帮助。
目的编写 bash 脚本, 实现一行命令得到 Android 手机录制屏幕 gif 动图文件.
博主使用 ubuntu 系统, shell 为 bash. 这个脚本也可以用在 mac 系统上.
听说 windows 系统出了 ubuntu on windows, 不知道能不能使用这个脚本.
原理 adb shell screenrecord android 4.4 版本后系统内预置了一个 screenrecord 命令, 可以用来将屏幕录制为 MP4 格式. 具体命令格式可以通过 –help 参数查看:

$ adb shell screenrecord --help Usage: screenrecord [options] < filename> Android screenrecord v1.2.Records the device' s display to a .mp4 file.Options: --size WIDTHxHEIGHT Set the video size, e.g. " 1280x720" .Default is the device' s main display resolution (if supported), 1280x720 if not.For best results, use a size supported by the AVC encoder. --bit-rate RATE Set the video bit rate, in bits per second.Value may be specified as bits or megabits, e.g. ' 4000000' is equivalent to ' 4M' .Default 4Mbps. --bugreport Add additional information, such as a timestamp overlay, that is helpful in videos captured to illustrate bugs. --time-limit TIME Set the maximum recording time, in seconds.Default / maximum is 180. --verbose Display interesting information on stdout. --help Show this message.Recording continues until Ctrl-C is hit or the time limit is reached.

举例:

adb shell screenrecord --size " 360x640" --bit-rate 2000000 /sdcard/android_screenrecord_test.mp4

上面的命令将把所连接的手机屏幕录制为宽高 360x640, 比特率 2M 的视频, 保存为手机 sd 卡根目录下的 android_screenrecord_test.mp4 文件.
该命令会持续录制, 直到用 ctrl-c 终止命令, 那么录制也就结束了.
也可以用 –time-limit TIME 参数来预先指定录制时长, 到时间会自动结束. 默认的最大时长为 3 分钟.
ffmpeg 使用 ffmpeg 抽帧的命令将视频提取为一系列图片:

ffmpeg -i video.mp4 -r 5 ' frames/frame-%03d.jpg'

其中: -r 5 代表抽取的帧率, 即每秒视频抽取 5 帧出来.
convert 使用 imagemagick 包中的 convert 命令将一系列图片组合为 gif 动图格式:

convert -delay 20 -loop 0 *.jpg myimage.gif

其中: -delay 20 代表所生成的 gif 动图每帧之间的时间间隔, 即每 0.2 秒显示下一帧.

如果系统内还没有 convert 命令, 可以用如下命令安装:
sudo apt-get install imagemagick
博主使用 ubuntu 16.10, 这个命令是预置在系统里的, 不需要安装.

ffmpeg 及 convert 参数设置上面两个命令中, ffmpeg -r 5 和 convert -delay 20 这两个参数值, 分别是视频抽帧间隔和 gif每帧间隔, 假设其分别为 video_fps 和 gif_delay, 那么这两个参数在设置时必须满足如下条件:

video_fps * gif_delay =
 100

如果乘积小于 100, 则生成的 gif 会比原本的播放速度快;
如果乘积大于 100, 则生成的 gif 会比原本的播放速度慢.
至于原因, 结合上面对这两个参数的介绍, 思考一下就明白了.
捕获录制结束事件上面三个命令分开调用, 实现录屏为 gif 已经相当简单了.
如果要将三条命令写在一个脚本里, 在一个过程中完成功能, 第一个要解决的是如何捕获录制结束事件, 即 ctrl-c 命令.
在 bash 中可以通过下面脚本实现:

# catch ctrl-c signal CTRL_C() { # ctrl-c hit, do something } trap CTRL_C SIGINT

有了这个方法获取录制结束事件, 再往下就简单了.
这里遇到一个坑, 就是如果捕获 ctrl-c 后直接开始转换 gif 的操作, 会失败. 试过几次后, 发现是 ctrl-c 后其实 Android 的 screenrecord 命令并没有处理完, 这时候的视频还不可用. 解决的办法简单粗暴, 让脚本原地 sleep 2秒, 再去操作所生成的 MP4 文件就可用了.
最终脚本也不知道该写些啥了, 直接贴出完整脚本吧:

#!/bin/bash # author : liuxu-0703@ 163.com#= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = # define param group hereQUALITY_1= (" 360x640" 1000000425) QUALITY_2= (" 360x640" 1000000520) QUALITY_3= (" 360x640" 10000001010) QUALITY_4= (" 720x1280" 1000000425) QUALITY_5= (" 720x1280" 1000000520)#= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = QUALITY= (${QUALITY_2[@ ]})RESOLUTION= ${QUALITY[0]} BIT_RATE= ${QUALITY[1]} GIF_FPS= ${QUALITY[2]} GIF_DELAY= ${QUALITY[3]}# GIF_FPS and GIF_DELAY must meet the following condition: # GIF_FPS * GIF_DELAY = 100OUTPUT_FILE_NAME= android_screen_record.$(date + %m%d%H%M%S).gif OUTPUT_FILE_DIR= $(pwd) OUTPUT_VIDEO_NAME= screenrecord_$(date + %m%d%H%M%S).mp4 OUTPUT_VIDEO_DEVICE_DIR= /sdcard TMP_DIR= /tmp/android_screen_to_gif_$(date + %m%d%H%M%S)RECORDING= true# you may use adb by absolute file path. if so, specify it here ADB= " adb" #= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = # catch ctrl-c signal CTRL_C() { if $RECORDING; then echo " stop recording. start convert..." RECORDING= false else # ctrl-c hit but not for stop recording, just exit. exit $? fi# adb screenrecord may still deal with mp4 file creating, # just wait for it a little while. sleep 2s adb pull $OUTPUT_VIDEO_DEVICE_DIR/$OUTPUT_VIDEO_NAME $TMP_DIR if [ -f $TMP_DIR/$OUTPUT_VIDEO_NAME ]; then # remove video on phone adb shell rm $OUTPUT_VIDEO_DEVICE_DIR/$OUTPUT_VIDEO_NAMEecho " converting file: $TMP_DIR/$OUTPUT_VIDEO_NAME" MP4ToGIF $TMP_DIR/$OUTPUT_VIDEO_NAME else echo " * create screen record mp4 fail" exit 2 fi } trap CTRL_C SIGINT# catch script exit event CLEAR_WORK() { if [ -e $TMP_DIR ]; then # since the tmp files have been put into /tmp/ dir, they will get # removed on system reboot. thus we are in no hurry to remove them now. # un-commit this line if you want to remove tmp files immediately after script run #rm $TMP_DIR echo fi } trap " CLEAR_WORK" EXIT#= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = function MP4ToGIF() { echo " *** extract frames ***" mkdir $TMP_DIR/frames ffmpeg -i $1 -r $GIF_FPS " $TMP_DIR/frames/frame-%03d.jpg" echo " *** convert frames to gif ***" convert -delay $GIF_DELAY -loop 0 " $TMP_DIR/frames/*.jpg" $OUTPUT_FILE_DIR/$OUTPUT_FILE_NAME }#= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = if [ ! -d " $OUTPUT_FILE_DIR" ]; then echo " * output dir not exists: $OUTPUT_FILE_DIR" exit 1 fi if [ ! -e $TMP_DIR ]; then mkdir $TMP_DIR fi if [ ! -e $TMP_DIR ]; then echo " * tmp dir not exists: $TMP_DIR" exit 1 fiecho " params: $RESOLUTION, $BIT_RATE, $GIF_FPS, $GIF_DELAY" adb shell screenrecord --verbose --size $RESOLUTION --bit-rate $BIT_RATE $OUTPUT_VIDEO_DEVICE_DIR/$OUTPUT_VIDEO_NAME

开头定义的那几个数组, 是为了便于测试. 最终生成的 gif 文件也直接保存在了当前目录下.
主要是因为加上参数化, 代码会多很多, 就不容易找到主要功能了.
带参数化, 带简易帮助文档的完整脚本, 可以在下面链接中找到:
android_screen2gif.sh
使用使用前提:

adb 可以正常连接到手机, 就是不能有 offline 之类的问题. (这里安利另一篇文章: 解决 ubuntu adb 设备识别问题)
手机必须是 4.4 以上系统.

脚本本身就是为了使用简单写的. 只需在命令行直接执行脚本, 即可开始手机屏幕录制. 因为是测试, 选在 /tmp 目录操作.

$ cd /tmp/ $ android_screen2gif.sh params: 360x640, 1000000, 5, 20 Main display is 720x1280 @ 60.00fps (orientation= 0) Configuring recorder for 360x640 video/avc at 1.00Mbps Content area is 360x640 at offset x= 0 y= 0

这时录制正在进行, 命令行挂起. 等你认为录制可以结束了, 按下 ctrl-c, 录制结束, 开始转换 gif 的步骤. 一般需要3到4秒, 录屏的 gif 就在当前目录生成了.

^Cstop recording. start convert... [100%] /sdcard/screenrecord_0407090859.mp4 converting file: /tmp/android_screen_to_gif_0407090859/screenrecord_0407090859.mp4 *** extract frames *** ffmpeg version 3.0.7-0ubuntu0.16.10.1 Copyright (c) 2000-2017 the FFmpeg developers ...... Input #0, mov,mp4,m4a,3gp,3g2,mj2, from ' /tmp/android_screen_to_gif_0407090859/screenrecord_0407090859.mp4' : ...... Output #0, image2, to ' /tmp/android_screen_to_gif_0407090859/frames/frame-%03d.jpg' : ...... *** convert frames to gif *** result gif file: /tmp/android_screen_record.0407090859.gif

这一步输出较多, 用 ...... 代替了部分输出. 最后那行就是最终生成的 gif 录屏文件了.
参数建议根据自测及最终 gif 生成的过程, 可以得到如下结论:
视频解析度参数:
宽高越大越清晰, 最终生成的 gif 文件越大. 这个是很明显的.
最好按手机竖屏显示的方式, 将解析度设置为 9:16 的比例. 如果设置为其他比例, 比如 480:480, 则录制出的视频会有很宽的黑边.
【一键生成 Android 录屏 gif 的脚本】视频比特率参数:
先说结论: 比特率设置基本不会影响最终生成的 gif 文件质量.
因为最终 gif 文件来自视频抽帧, 视频比特率的大小对于比如每秒抽取10帧这样的需求, 对抽取出的图片清晰度影响不大. 因此为了中间文件更小, 建议把这个参数设低即可.
抽帧帧率及每帧间隔:
这两个参数对最终 gif 质量影响很大. 其中:
抽帧帧率越大, 最终 gif 质量越高;
每帧间隔越小, 最终 gif 质量越高.
如前述, 这两个参数必须成对设置. 如果这两个参数都取整数的话, 基本上可以设置的就下面这几对:

2, 50 4, 25 5, 20 10, 10

其中:
10, 10 这组, 设置每秒10帧, gif 每帧间隔 0.1 秒, 这样5秒的gif文件就要大概 10M 大小了.
2, 50 这组, 设置每秒2帧, gif 每帧间隔 0.5 秒, 最终gif文件卡顿就很严重了.
因此建议选取 5, 20 这组参数. 如果对gif质量要求很高, 可以试试 10, 10 这组参数.
综上, 小伙伴们可以自己尝试下设置不同的参数组合, 试几次就能体会该怎么设置了.
参考: