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。
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）

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

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，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