with ffmpeg to encode video for live streaming and for recording to files for on-demand playback
We've been doing some experimentation with ffmpeg to encode video for live streaming and for recording to files for on-demand playback. While I've been impressed by the capabilities of ffmpeg, I've found that its command-line processing is quite daunting. Here I provide a set of command-line options along with commentary on what is going on.
One of the most frustrating things I've found in trying to learn ffmpeg is that many examples online are quite out-of-date. It seems that ffmpeg has changed its command-line options fairly frequently. So many of the examples you'll find won't work.
The example that follows uses a snapshot of the ffmpeg subversion code from September 10, 2009.
Ready?
Are you sure?
Here is the command line:
- ffmpeg -f rawvideo -pix_fmt yuv422p \
-s 720x486 -r 29.97 \
-i /tmp/vpipe \
-ar 48000 -f s16le -ac 2 -i /tmp/apipe \
-vol 4096 \
-acodec libfaac -ac 2 -ab 192k -ar 44100 \
-async 1 \
-vcodec libx264 -vpre default -threads 0 \
-croptop 6 -cropbottom 6 -cropleft 9 -cropright 9 \
-r 20 -g 45 -s 432x324 -b 1024k -bt 100k \
-deinterlace \
-y \
'/tmp/encoding-0001.mp4' \
-an \
-vcodec libx264 -vpre default -threads 0 \
-croptop 6 -cropbottom 6 -cropleft 9 -cropright 9 \
-r 20 -g 45 -s 432x324 -b 1024k -bt 100k \
-deinterlace \
-vglobal 1 \
-f rtp rtp://127.0.0.1:9012 \
-vn \
-vol 4096 \
-acodec libfaac -ac 2 -ab 192k -ar 44100 \
-async 1 \
-flags +global_header \
-f rtp rtp://127.0.0.1:9014 \
-newaudio \
-an \
-vcodec libx264 -vpre default -threads 0 \
-croptop 6 -cropbottom 6 -cropleft 9 -cropright 9 \
-r 15 -g 45 -s 432x324 -b 768k -bt 50k \
-deinterlace \
-vglobal 1 \
-f rtp rtp://127.0.0.1:9008 \
-newvideo \
-vn \
-vol 4096 \
-acodec libfaac -ac 2 -ab 128k -ar 44100 \
-async 1 \
-flags +global_header \
-f rtp rtp://127.0.0.1:9010 \
-newaudio
Don't be intimidated. We'll break this thing down line-by-line.
Specifying the input
- ffmpeg -f rawvideo -pix_fmt yuv422p \
-s 720x486 -r 29.97 \
-i /tmp/vpipe \
Everything up to the -i option describes what is contained in the input file /tmp/vpipe. In this case, our input video is raw (uncompressed) frame data in the YUV 4:2:2 planar format, 720 pixels wide by 486 pixels high, with a frame rate of 29.97 frames per second. Note that these options must precede the -i option. If any of these options came after the -i, ffmpeg would think that they belonged to the next input file specified.
- -ar 48000 -f s16le -ac 2 -i /tmp/apipe \
Now we're telling ffmpeg what the audio looks like in the input file /tmp/apipe. We have a sample rate of 48000 samples per second; each sample is signed 16-bit, little endian, and there are 2 audio channels.
Specifying the output
The next set of options describes the output format, for both audio and video. I do not believe that the order within these options is critical, but I like to group them logically so that all the audio options are together and all the video options are together.
- -vol 4096 \
-acodec libfaac -ac 2 -ab 192k -ar 44100 \
-async 1 \
The -vol option indicates that we're going to adjust the audio levels. The baseline value is 256. I have not seen good documentation on the valid values here, but I've used values like 512, 1024, 2048, and 4096 to bump up the volume. Picking the right value here requires some experimentation and depends heavily on the levels in your original source.
We're going to output AAC audio using the libfaac encoder. ffmpeg has a built-in AAC encoder, but it doesn't seem to be as robust as that provided by libfaac. If you want AAC, and your version of ffmpeg was linked against libfaac, I would recommend that you use it.
The AAC will be 2 channels, 192kbps, with a sample rate of 44100 Hz.
Finally, the -async option indicates that ffmpeg should use audio/video sync method 1, which adjusts the start of the video and audio tracks, but does not do any time stretching over the course of the tracks.
- -vcodec libx264 -vpre default -threads 0 \
-croptop 6 -cropbottom 6 -cropleft 9 -cropright 9 \
-r 20 -g 45 -s 432x324 -b 1024k -bt 100k \
-deinterlace \
Here we are specifying our video output options. We're going to use H.264 compression, as provided by the libx264 library. The -vpre option means that we will use the default quality preset (note that when using libx264 to encode, you can specify two -vpre options. The first is quality, and the second is the profile to use (main, baseline, etc., with "main" being the default). I have not seen this documented very well.
The -threads 0 option instructs ffmpeg to use the optimal number of threads when encoding.
We are going to crop our video a few pixels around the border, as we were getting some noise around the edges of our source video.
The -r option specifies that our output will be 20 frames per second. The -g option is the "group of pictures" (GOP) size, which is the number of frames between keyframes. With a smaller number, your output will have more keyframes, which means that streaming clients will be able to recover more quickly if they drop packets for some reason. It also will have a detrimental effect on file size.
The -s option specifies our frame size, the -b option specifies the desired bitrate, and the -bt option is the bitrate tolerance. ffmpeg will try to keep the video close to the desired bitrate, and the tolerance tells it how much leeway it has above and below the target bitrate.
Finally, we are deinterlacing the video, as the source was NTSC interlaced video. Without deinterlacing, you can see some very unpleasant "comb" artifacts in your digitized video.
- -y \
'/tmp/encoding-0001.mp4' \
Here we specify the output file. The -y option instructs ffmpeg to overwrite the file without asking for confirmation. ffmpeg will infer the file format from the filename extension. Here it will be writing to an MPEG4 file.
Adding another output
Now we are going to add some specs for RTP output. We will send this RTP stream over the network to a Wowza server, which can convert the RTP to RTMP for playback in Flash clients.
Unlike when we wrote to an MPEG4 file, RTP requires that we break the audio and video into two separate streams.
- -an \
-vcodec libx264 -vpre default -threads 0 \
-croptop 6 -cropbottom 6 -cropleft 9 -cropright 9 \
-r 20 -g 45 -s 432x324 -b 1024k -bt 100k \
-deinterlace \
-vglobal 1 \
-f rtp rtp://127.0.0.1:9012 \
You'll notice that most of these specs are the same as what we specified for our MPEG4 output. But there are a few differences. Let's focus on those. The -an option tells ffmpeg to remove the audio stream from this output. The -vglobal 1 option instructs ffmpeg to use out-of-band global headers in the video stream (as opposed to in-band). This may help some players interpret the video stream.
Finally, we specify the output format as "rtp" with the -f option, and instead of a filename, we have a URL that indicates where ffmpeg should send the RTP packets.
Next we specify the audio output:
- -vn \
-vol 4096 \
-acodec libfaac -ac 2 -ab 192k -ar 44100 \
-async 1 \
-flags +global_header \
-f rtp rtp://127.0.0.1:9014 \
-newaudio \
Again, this is very similar to the options we provided for our MPEG4 output, with some notable differences. First, we use the -vn option to indicate that this output does not contain video. The -flags +global_header is used to force ffmpeg to spit out some important audio specifications in the SDP it generates (you use an SDP file on the Wowza server to connect the RTMP stream to the RTP stream; Wowza needs to know all about the audio and video to interpret it properly).
Again, we specify the rtp format with the -f option, and we provide a URL. Note that the port number is different. It is customary for RTP streams to use two ports with an open port between them. The ports just after each of the RTP ports will be used for RTCP ports (in our example, ports 9013 and 9015 wil be used), where the receiver communicates back to the sender.
The last option, -newaudio, restores the audio stream that got killed off by the -an option earlier. Note that -newaudio is a special option; it only modifies the output which immediately precedes it. This is one of those cases where order of options is critical.
With these options, we are now writing to an MPEG4 file and streaming RTP simultaneously. But wait, there's more...
Adding another RTP stream
Our first RTP stream uses about 1200 Kbps with audio and video combined. Let's create an option for our bandwidth-deprived visitors to use.
We can tack on another pair of outputs, one for video and one for audio:
- -an \
-vcodec libx264 -vpre default -threads 0 \
-croptop 6 -cropbottom 6 -cropleft 9 -cropright 9 \
-r 15 -g 45 -s 432x324 -b 256k -bt 50k \
-deinterlace \
-vglobal 1 \
-f rtp rtp://127.0.0.1:9008 \
-newvideo \
-vn \
-vol 4096 \
-acodec libfaac -ac 1 -ab 64k -ar 44100 \
-async 1 \
-flags +global_header \
-f rtp rtp://127.0.0.1:9010 \
-newaudio
There are a few differences between our second set of RTP outputs and the first:
- the video framerate is 15 (-r 15)
- the video bitrate is 256kbps and the tolerance is 50kbps (-b 256k -bt 50k)
- the audio is single channel (-ac 1)
- the audio is 64kbps (-ab 64k)
- the ports are different in the RTP URLs
You'll also notice that there is a -newvideo option after the video RTP URL. That's because our previous output was audio-only, due to the -vn option. Using the -newvideo option restores the video stream to this output. Without it, you'd have no audio (because of the -an), and no video (because of the -vn in the previous output).
So now we're writing to an MPEG4 file and streaming at two different bitrates simultaneously! Pretty sweet.
I won't get into the specifics here of how you get the SDP file from ffmpeg, put it on the Wowza server, and connect to the Wowza server with a flash-based player. There are lots of docs and notes in the Wowza forums on how to do that.
with ffmpeg to encode video for live streaming and for recording to files for on-demand playback的更多相关文章
- [quote ]ffmpeg, gstreamer, Raspberry Pi, Windows Desktop streaming
[quote ]ffmpeg, gstreamer, Raspberry Pi, Windows Desktop streaming http://blog.pi3g.com/2013/08/ffmp ...
- ffmpeg的内部Video Buffer管理和传送机制
ffmpeg的内部Video Buffer管理和传送机制 本文主要介绍ffmpeg解码器内部管理Video Buffer的原理和过程,ffmpeg的Videobuffer为内部管理,其流程大致为:注册 ...
- Video Codecs by FOURCC 视频格式编码
FOURCC Name Summary 1978 A.M.Paredes predictor This is a LossLess video codec. >>> 2VUY 2VU ...
- Install FFmpeg, Mplayer, Mencoder, MP4Box, Flvtool2
You can use the following tutorial to install ffmpeg and other video modules in your centos server.F ...
- Linux下编译带x264的ffmpeg的配置方法,包含SDL2
一.环境准备 ffmpeg下载:http://www.ffmpeg.org/download.html x264下载:http://download.videolan.org/x264/snapsho ...
- 基于ffmpeg的简单音视频编解码的例子
近日需要做一个视频转码服务器,对我这样一个在该领域的新手来说却是够我折腾一番,在别人的建议下开始研究开源ffmpeg项目,下面是在代码中看到的一 段例子代码,对我的学习非常有帮助.该例子代码包含音频的 ...
- 最简单的基于FFmpeg的编码器-纯净版(不包含libavformat)
===================================================== 最简单的基于FFmpeg的视频编码器文章列表: 最简单的基于FFMPEG的视频编码器(YUV ...
- Linux---centos编译安装ffmpeg
环境 系统环境:CentOS release 6.7 (Final) 需求 编译安装ffmpeg 获取依赖 安装依赖包 yum install -y autoconf automake cmake f ...
- FFmpeg使用基础
本文为作者原创,转载请注明出处:https://www.cnblogs.com/leisure_chn/p/10297002.html 本文介绍FFmpeg最基础的概念,了解FFmpeg的简单使用,帮 ...
随机推荐
- 调起qq临时通话
1.在qq推广的网站上的推广工具中将个人或者公司的qq确认为推广qq 2. 选择好显示的图片,将代码拷贝到页面上就可以了
- Hacker(十一)----黑客常用入侵方法
Internet中,为了防止黑客入侵自己的电脑,就必须了解黑客入侵目标计算机的常用方法.黑客常用的入侵方法有数据驱动攻击.系统文件非法利用.伪造信息攻击.远端操纵等. 一.数据驱动攻击 数据驱动攻击是 ...
- ASP.NET母版与内容页相对路径的问题
1. 图片问题 非常好解决 <img runat="server" src="~/images/ad468x60.gif" alt="" ...
- HTML基础知识笔记(二)
HTML <img>标签 语法: <img src="图片地址" alt="下载失败时的替换文本" title = "提示文本&qu ...
- asp.net 页面上传文件控件后台代码Request.Files获取不到
今天开发中遇到页面文件上传控件选择了文件,而后台Request.Files.Count取值为0,之前开发中遇到过几次,老是忘掉,今天记下来. html: <input type="fi ...
- 2014年1月9日 Oracle常见授权与权限回收[转]
1.GRANT 赋于权限 常用的系统权限集合有以下三个: CONNECT(基本的连接), RESOURCE(程序开发), DBA(数据库管理) 常用的数据对象权限有以下五个: ALL ON 数据对象名 ...
- tableView特色用法
// // ViewController.m // UITableView // // Created by yhj on 15/12/15. // Copyright © 2015年 QQ: ...
- Array类型(一)
1.创建数组的基本方式有两种,第一种使用Array构造函数 使用Array构造函数时可以省略new操作符 2.第二种方式是使用数组字面量表示法 由于IE的实现与其他浏览器不一致,因此我们不赞同使用这个 ...
- Ecstore的微信账号绑定会员免登录
在微信公众号中通过消息交互/自定义菜单,可直接登录Ecstore手机商城.如果想用原商城账号登录,可以通过登录绑定,在后台可以获取登录绑定的链接这个链接可以在微信公众号消息交互场景或自定义菜单中使用, ...
- 【Ecstore】为自建模块添加自定义主题模板
做好ECSOTRE模块后,需在主题中添加模板,而添加模板页面时只有产品分类页.产品详细页.首页等内置模块的模板类型. 下面介绍如何添加一个自定义的模板类型“buildings”. 一.修改(建议复制到 ...