FFmpeg简介及常见用法

约定不等于承诺〃 2023-05-30 15:53 43阅读 0赞

本文主要介绍 FFmpeg（Fast Forward MPEG）的相关知识及其常见用法。

# 1 概述 #

引用官网的介绍：

FFmpeg is the leading multimedia framework, able to decode, encode, transcode, mux, demux, stream, filter and play pretty much anything that humans and machines have created. It supports the most obscure ancient formats up to the cutting edge. No matter if they were designed by some standards committee, the community or a corporation. It is also highly portable: FFmpeg compiles, runs, and passes our testing infrastructure FATE across Linux, Mac OS X, Microsoft Windows, the BSDs, Solaris, etc. under a wide variety of build environments, machine architectures, and configurations.

引用官方的简介：

A complete, cross-platform solution to record, convert and stream audio and video.

简单说，FFmpeg 提供了一个跨平台的解决方案，其包含了视音频的记录（采集）、编解码、格式转换和流化功能。

使用 FFmpeg 进行视音频的转换非常容易，例如使用如下命令将视频由mp4格式转换为avi格式：

ffmpeg -i input.mp4 output.avi

# 2 包含的工具和库 #

## 2.1 包含的工具 ##

当前 FFmpeg 包含以下几种工具：

*  ffmpeg: a command line tool to convert multimedia files between formats.
 *  ffplay: a simple media player based on SDL and the FFmpeg libraries.
 *  ffprobe: a simple multimedia stream analyzer.

## 2.1 包含的库 ##

当前 FFmpeg 包含以下几种库：

*  **libavutil**: libavutil is a library containing functions for simplifying programming, including random number generators, data structures, mathematics routines, core multimedia utilities, and much more.
 *  **libavcodec**: libavcodec is a library containing decoders and encoders for audio/video codecs.
 *  **libavformat**: libavformat is a library containing demuxers and muxers for multimedia container formats.
 *  **libavdevice**: libavdevice is a library containing input and output devices for grabbing from and rendering to many common multimedia input/output software frameworks, including Video4Linux, Video4Linux2, VfW, and ALSA.
 *  **libavfilter**: libavfilter is a library containing media filters.
 *  **libswscale**: libswscale is a library performing highly optimized image scaling and color space/pixel format conversion operations.
 *  **libswresample**: libswresample is a library performing highly optimized audio resampling, rematrixing and sample format conversion operations.

# 3 Linux平台下的常见用法 #

本章介绍在 Linux 平台下的 ffmpeg 命令的常见用法。

注意：对于重复出现的 ffmpeg 命令选项，只在该选项首次出现时进行介绍。

## 3.1 将本地视频文件转为直播流 ##

示例命令如下：

ffmpeg -re -i feast-2880x1440.mp4 -codec copy -f flv rtmp://192.168.110.168:1935/live/zb

上面的命令将本地视频文件 feast-2880x1440.mp4 转换为直播流 rtmp://192.168.110.168:1935/live/zb。

下面详细介绍上面的命令中涉及的选项。

**-re (input)**: Read input at native frame rate. Mainly used to simulate a grab device, or live input stream (e.g. when reading from a file). Should not be used with actual grab devices or live input streams (where it can cause packet loss). By default ffmpeg attempts to read the input(s) as fast as possible. This option will slow down the reading of the input(s) to the native frame rate of the input(s). It is useful for real-time output (e.g. live streaming).

**-i url (input)**: input file url

**-codec\[:stream\_specifier\] codec (input/output,per-stream)**：Select an encoder (when used before an output file) or a decoder (when used before an input file) for one or more streams. codec is the name of a decoder/encoder or a special value "copy" (output only) to indicate that the stream is not to be re-encoded.

说明：当前ffmpeg版本支持的“codec”的值，可通过下列命令查询：

ffmpeg -codecs

本示例用到了 -codec copy 的用法，即 **stream copy** 的概念。关于 **stream copy**，解释如下：

Stream copy is a mode selected by supplying the copy parameter to the -codec option. It makes ffmpeg omit the decoding and encoding step for the specified stream, so it does only demuxing and muxing. It is useful for changing the container format or modifying container-level metadata. The diagram above will, in this case, simplify to this:

_______              ______________            ________
    |       |            |              |          |        |
    | input |  demuxer   | encoded data |  muxer   | output |
    | file  | ---------> | packets      | -------> | file   |
    |_______|            |______________|          |________|

Since there is no decoding or encoding, it is very fast and there is no quality loss. However, it might not work in some cases because of many factors. Applying filters is obviously also impossible, since filters work on uncompressed data.

**-f fmt (input/output)**: Force input or output file format. The format is normally auto detected for input files and guessed from the file extension for output files, so this option is not needed in most cases.

## 3.2 从视频文件中提取H264数据 ##

示例命令如下：

ffmpeg -i video_AFP.mp4 -c:v copy -bsf:v h264_mp4toannexb -an video_AFP.h264

上面的命令从本地视频文件 video\_AFP.mp4 中提取H264数据，并导出至转换文件 video\_AFP.h264 中。

下面详细介绍上面的命令中涉及的选项。

**-c\[:stream\_specifier\] codec (input/output,per-stream)**: 等同于前文介绍的选项“-codec\[:stream\_specifier\] codec (input/output,per-stream)”。

**-bsf\[:stream\_specifier\] bitstream\_filters (output,per-stream)**: Set bitstream filters for matching streams. bitstream\_filters is a comma-separated list of bitstream filters. Use the "-bsfs" option to get the list of bitstream filters.

**-an (input/output)**:

*  As an input option, blocks all audio streams of a file from being filtered or being automatically selected or mapped for any output. See "-discard" option to disable streams individually.
 *  As an output option, disables audio recording i.e. automatic selection or mapping of any audio stream. For full manual control see the "-map" option.

## 3.3 捕获直播流内容并存储在本地（或转发） ##

示例命令如下：

ffmpeg -i rtsp://10.11.111.161:8554/live -codec copy -y capture.mp4

上面的命令捕获 rtsp 协议直播流的内容，并将捕获到的内容存储到本地文件“capture.mp4”中。如果想要将捕获到的内容进行转发，则使用直播流URL替换本地文件名称即可。

**-y (global)**: Overwrite output files without asking.