FFmpeg流媒体（7）

FFmpeg生成DASH流

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1、DASH参数说明

ffmpeg -h muxer=dash

Muxer dash [DASH Muxer]:
    Common extensions: mpd.
    Default video codec: h264.
    Default audio codec: aac.
dash muxer AVOptions:
  -adaptation_sets   <string>     E........ Adaptation sets. Syntax: id=0,streams=0,1,2 id=1,streams=3,4 and so on
  -window_size       <int>        E........ number of segments kept in the manifest (from 0 to INT_MAX) (default 0)
  -extra_window_size <int>        E........ number of segments kept outside of the manifest before removing from disk (from 0 to INT_MAX) (default 5)
  -min_seg_duration  <int>        E........ minimum segment duration (in microseconds) (will be deprecated) (from 0 to INT_MAX) (default 5e+06)
  -seg_duration      <duration>   E........ segment duration (in seconds, fractional value can be set) (default 5)
  -remove_at_exit    <boolean>    E........ remove all segments when finished (default false)
  -use_template      <boolean>    E........ Use SegmentTemplate instead of SegmentList (default true)
  -use_timeline      <boolean>    E........ Use SegmentTimeline in SegmentTemplate (default true)
  -single_file       <boolean>    E........ Store all segments in one file, accessed using byte ranges (default false)
  -single_file_name  <string>     E........ DASH-templated name to be used for baseURL. Implies storing all segments in one file, accessed using byte ranges
  -init_seg_name     <string>     E........ DASH-templated name to used for the initialization segment (default "init-stream$RepresentationID$.m4s")
  -media_seg_name    <string>     E........ DASH-templated name to used for the media segments (default "chunk-stream$RepresentationID$-$Number%05d$.m4s")
  -utc_timing_url    <string>     E........ URL of the page that will return the UTC timestamp in ISO format
  -method            <string>     E........ set the HTTP method
  -http_user_agent   <string>     E........ override User-Agent field in HTTP header
  -http_persistent   <boolean>    E........ Use persistent HTTP connections (default false)
  -hls_playlist      <boolean>    E........ Generate HLS playlist files(master.m3u8, media_%d.m3u8) (default false)
  -streaming         <boolean>    E........ Enable/Disable streaming mode of output. Each frame will be moof fragment (default false)
  -timeout           <duration>   E........ set timeout for socket I/O operations (default -0.000001)
  -index_correction  <boolean>    E........ Enable/Disable segment index correction logic (default false)
  -format_options    <string>     E........ set list of options for the container format (mp4/webm) used for dash
  -dash_segment_type <int>        E........ set dash segment files type (from 0 to 1) (default mp4)
     mp4                          E........ make segment file in ISOBMFF format
     webm                         E........ make segment file in WebM format

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2、window_size与extra_window_size参数说明

与HDS设置类似，DASH参数设置同样支持window_size与extra_window_size，设置列表中的切片个数与列表外切片的保留个数，设置如下：

ffmpeg -re -i 111.mp4 -c:v copy -acodec copy -f dash -window_size 4 -extra_window_size 3 index.mpd

执行完毕后会生成文件索引列表index.mpd，文件列表长度为4个切片长度，切片之外保留3个切片，在DASH直播格式中，音视频是分开切片的，即视频分为一路切片，音频分为一路切片，各有7个。另外还有2个初始化信息切片，1个索引切片。

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3、single_file参数说明

FFmpeg支持生成DASH时将切片列表中的文件写入到一个文件中，使用single_file参数即可，命令如下：

ffmpeg -re -i 111.mp4 -c:v copy -acodec copy -f dash -window_size 4 -extra_window_size 3 -single_file 1 index.mpd

命令执行完成后，目录中会生成3个文件：1个索引文件、1个音频文件、1个视频文件。

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