我希望使用手机内置播放器拍摄相机，在我的应用中播放透明视频。我尝试用Android设备的alpha通道编码我的视频：
ffmpeg -i "Comp.avi" -c:v libvpx -pix_fmt yuva420p -metadata:s:v:0 alpha_mode="1" output.webm
结果非常好，但我在Android手机上播放时有滞后（不时冻结视频）。是否有选项来提高解码性能？
某些控制台输出：
D:\SOFT\ffmpeg-20160207-git-9ee4c89-win64-static\bin>ffmpeg -i "d:\temp\cherti\Comp 1.avi" -c:v libvpx -pix_fmt yuva420p -metadata:s:v:0 alpha_mode="1" d:\temp\cherti\output.webm
ffmpeg version N-80386-g5f5a97d Copyright (c) 2000-2016 the FFmpeg developers
built with gcc 5.4.0 (GCC)
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-nvenc --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmfx --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-decklink --enable-zlib
libavutil 55. 24.100 / 55. 24.100
libavcodec 57. 46.100 / 57. 46.100
libavformat 57. 38.100 / 57. 38.100
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 46.101 / 6. 46.101
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 1.100 / 2. 1.100
libpostproc 54. 0.100 / 54. 0.100
Input #0, avi, from 'd:\temp\cherti\Comp 1.avi':
Metadata:
date : 2017-02-18T14:10:42.00916
encoder : Adobe After Effects CC 2015 (Windows)
Duration: 00:00:05.00, start: 0.000000, bitrate: 1592542 kb/s
Stream #0:0: Video: rawvideo, bgra, 1080x1920, 1605907 kb/s, 24 fps, 24 tbr, 24 tbn, 24 tbc
File 'd:\temp\cherti\output.webm' already exists. Overwrite ? [y/N] y
[libvpx @ 0000000002593640] v1.5.0
[webm @ 00000000025a54e0] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
Output #0, webm, to 'd:\temp\cherti\output.webm':
Metadata:
date : 2017-02-18T14:10:42.00916
encoder : Lavf57.38.100
Stream #0:0: Video: vp8 (libvpx), yuva420p, 1080x1920, q=-1--1, 200 kb/s, 24 fps, 1k tbn, 24 tbc
Metadata:
alpha_mode : 1
encoder : Lavc57.46.100 libvpx
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream mapping:
Stream #0:0 -> #0:0 (rawvideo (native) -> vp8 (libvpx))