在手机web中播放视频（使用js，不使用video标签，支持直播）

主要原理是使用 jsmpeg（Github链接） 。

jsmpeg是js中解析mpeg视频，并把内容画在画布上。

这篇文章是记录jsmpeg怎么用的。

目前发现jsmpeg的不足

1. 无法播放声音，只能播放视频。（2018年更新，官方已解决该问题）
2. 在苹果和性能低的安卓中卡顿严重（iPhone7有略微卡顿，部分2016年安卓旗舰机不卡，现在终于相信有安卓能秒苹果了）
3. 目前（2018年）版本使用ts格式的视频，相同质量的视频大小差不多是mp4的两倍，太占流量了
4. 缺少许多事件

解决不足

1. 用audio播放
2. 无法解决，我本来想自己开启webgl，结果看到jsmpeg就是用的webgl，就是说他自己已经解决过了的。随着大家手机的升级，已经不卡了
3. 也无法解决，只能在体积和可操作性上做取舍了
4. 我自己增加了几个事件：https://gitee.com/haua/jsmpeg...

视频源

直播流

jsmpeg支持直播流，但是我还没研究，所以只是先提一下，先不深入。

视频文件

jsmpeg只支持mpeg格式的视频（目前2018版本支持ts视频格式，似乎是不支持mpeg了？），jsmpeg官方建议用ffmpeg来转格式。ffmpeg下载地址

1. 从把视频转成mpg格式（转出的视频无音频，且应该是支持从许多种格式转过来的，我暂时只试过从mp4转）
   ./ffmpeg -i video.mp4 -f mpeg1video -vf "crop=iw-mod(iw,2):ih-mod(ih,2)" -b 0 video.mpg
2. 从视频中提取音频（上面说过jsmpeg不能播声音，所以声音要单独弄出来）
   ./ffmpeg -i video.mp4 -f mp3 -vn video.mp3

ffmpeg用法记录
Print help / information / capabilities:
-L show license
-h topic show help
-? topic show help
-help topic show help
--help topic show help
-version show version
-buildconf show build configuration
-formats show available formats
-devices show available devices
-codecs show available codecs
-decoders show available decoders
-encoders show available encoders
-bsfs show available bit stream filters
-protocols show available protocols
-filters show available filters
-pix_fmts show available pixel formats
-layouts show standard channel layouts
-sample_fmts show available audio sample formats
-colors show available color names
-sources device list sources of the input device
-sinks device list sinks of the output device
-hwaccels show available HW acceleration methods

Global options (affect whole program instead of just one file:
-loglevel loglevel set logging level
-v loglevel set logging level
-report generate a report
-max_alloc bytes set maximum size of a single allocated block
-y overwrite output files
-n never overwrite output files
-ignore_unknown Ignore unknown stream types
-stats print progress report during encoding
-max_error_rate ratio of errors (0.0: no errors, 1.0: 100% error maximum error rate
-bits_per_raw_sample number set the number of bits per raw sample
-vol volume change audio volume (256=normal)

Per-file main options:
-f fmt force format
-c codec codec name
-codec codec codec name
-pre preset preset name
-map_metadata outfile[,metadata]:infile[,metadata] set metadata information of outfile from infile
-t duration record or transcode "duration" seconds of audio/video
-to time_stop record or transcode stop time
-fs limit_size set the limit file size in bytes
-ss time_off set the start time offset
-sseof time_off set the start time offset relative to EOF
-seek_timestamp enable/disable seeking by timestamp with -ss
-timestamp time set the recording timestamp ('now' to set the current time)
-metadata string=string add metadata
-program title=string:st=number... add program with specified streams
-target type specify target file type ("vcd", "svcd", "dvd", "dv" or "dv50" with optional prefixes "pal-", "ntsc-" or "film-")
-apad audio pad
-frames number set the number of frames to output
-filter filter_graph set stream filtergraph
-filter_script filename read stream filtergraph description from a file
-reinit_filter reinit filtergraph on input parameter changes
-discard discard
-disposition disposition

Video options:
-vframes number set the number of video frames to output
-r rate set frame rate (Hz value, fraction or abbreviation)
-s size set frame size (WxH or abbreviation)
-aspect aspect set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)
-bits_per_raw_sample number set the number of bits per raw sample
-vn disable video
-vcodec codec force video codec ('copy' to copy stream)
-timecode hh:mm:ss[:;.]ff set initial TimeCode value.
-pass n select the pass number (1 to 3)
-vf filter_graph set video filters
-ab bitrate audio bitrate (please use -b:a)
-b bitrate video bitrate (please use -b:v)
-dn disable data

Audio options:
-aframes number set the number of audio frames to output
-aq quality set audio quality (codec-specific)
-ar rate set audio sampling rate (in Hz)
-ac channels set number of audio channels
-an disable audio
-acodec codec force audio codec ('copy' to copy stream)
-vol volume change audio volume (256=normal)
-af filter_graph set audio filters

Subtitle options:
-s size set frame size (WxH or abbreviation)
-sn disable subtitle
-scodec codec force subtitle codec ('copy' to copy stream)
-stag fourcc/tag force subtitle tag/fourcc
-fix_sub_duration fix subtitles duration
-canvas_size size set canvas size (WxH or abbreviation)
-spre preset set the subtitle options to the indicated preset