ffmpeg mp4上传到Twitter - 不支持的错误

Question

我创建了一个截屏视频，它被保存为webm。使用ffmpeg我将它转换为mp4：

尚不支持这种文件。请尝试上传gif，视频或图片。

ffmpeg -f input.webm -pix_fmt yuv420p -strict -2 output.mp4

我使用的是yuv420p，这就是本主题对twitter的说法 - https://twittercommunity.com/t/unable-to-upload-video-to-twitter/61721/3

然而，当我打开一个新标签，转到Twitter，点击照片图标，点击上传立即给我错误“那种文件尚不支持。请尝试上传gif，视频或图片。”它无法快速检查pix格式。现在还有人可以在这里发生什么？

这是ffmpeg控制台输出：

ffmpeg version 2.2.1 Copyright (c) 2000-2014 the FFmpeg developers
  built on Jun  9 2014 20:01:41 with emcc (Emscripten GCC-like replacement) 1.12.0 (commit 6960d2296299e96d43e694806f5d35799ef8d39c)
  configuration: --cc=emcc --prefix=/Users/bgrinstead/Sites/videoconverter.js/build/ffmpeg/../dist --enable-cross-compile --target-os=none --arch=x86_32 --cpu=generic --disable-ffplay --disable-ffprobe --disable-ffserver --disable-asm --disable-doc --disable-devices --disable-pthreads --disable-w32threads --disable-network --disable-hwaccels --disable-parsers --disable-bsfs --disable-debug --disable-protocols --disable-indevs --disable-outdevs --enable-protocol=file
  libavutil      52. 66.100 / 52. 66.100
  libavcodec     55. 52.102 / 55. 52.102
  libavformat    55. 33.100 / 55. 33.100
  libavdevice    55. 10.100 / 55. 10.100
  libavfilter     4.  2.100 /  4.  2.100
  libswscale      2.  5.102 /  2.  5.102
  libswresample   0. 18.100 /  0. 18.100
[vp8 @ 0xdde410] Warning: not compiled with thread support, using thread emulation
Input #0, matroska,webm, from 'input.webm':
  Metadata:
    encoder         : QTmuxingAppLibWebM-0.0.1
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0(eng): Video: vp8, yuv420p, 1920x1200, SAR 1:1 DAR 8:5, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
Incompatible pixel format 'yuv420p' for codec 'gif', auto-selecting format 'pal8'
[swscaler @ 0xdd7f40] No accelerated colorspace conversion found from yuv420p to bgr8.
[gif @ 0xde5290] Warning: not compiled with thread support, using thread emulation
[vp8 @ 0xdde410] Warning: not compiled with thread support, using thread emulation
Output #0, gif, to 'output/output.gif':
  Metadata:
    encoder         : Lavf55.33.100
    Stream #0:0(eng): Video: gif, pal8, 1920x1200 [SAR 1:1 DAR 8:5], q=2-31, 200 kb/s, 100 tbn, 30 tbc (default)
Stream mapping:
  Stream #0:0 -> #0:0 (vp8 -> gif)
Press [q] to stop, [?] for help
frame=    1 fps=0.0 q=0.0 size=       0kB time=00:00:00.03 bitrate=   8.5kbits/s    
frame=    6 fps=0.0 q=0.0 size=     640kB time=00:00:00.33 bitrate=15877.0kbits/s    
frame=   12 fps= 11 q=0.0 size=    1452kB time=00:00:00.63 bitrate=18878.9kbits/s    
frame=   17 fps= 10 q=0.0 size=    2080kB time=00:00:00.91 bitrate=18723.7kbits/s    
frame=   22 fps=9.6 q=0.0 size=    2698kB time=00:00:01.16 bitrate=19052.0kbits/s    
frame=   27 fps=9.7 q=0.0 size=    3294kB time=00:00:01.43 bitrate=18869.4kbits/s    
frame=   33 fps=9.6 q=0.0 size=    4001kB time=00:00:01.76 bitrate=18622.0kbits/s    
frame=   38 fps=9.5 q=0.0 size=    4567kB time=00:00:02.04 bitrate=18339.7kbits/s    
frame=   44 fps=9.5 q=0.0 size=    5236kB time=00:00:02.37 bitrate=18097.4kbits/s    
frame=   50 fps=9.7 q=0.0 size=    5902kB time=00:00:02.71 bitrate=17839.9kbits/s    
frame=   55 fps=9.6 q=0.0 size=    6457kB time=00:00:02.96 bitrate=17868.9kbits/s    
frame=   55 fps=9.6 q=0.0 Lsize=    6567kB time=00:00:02.96 bitrate=18175.9kbits/s    
video:6623kB audio:0kB subtitle:0 data:0 global headers:0kB muxing overhead -0.834044%

以下是截图：