title: Why won't some MP4 videos start streaming until the entire file is downloaded?
body: <p>I'm working on an application where users upload a video and play it back the browser using jwplayer, jplayer, flowplayer, etc. Some videos play immediately, while others wait until the entire video file has been downloaded.</p>
  
  <p>I'm using ffmpeg to convert the video to mp4 format. </p>
  
  <p>Here is some detailed information about one of the video files I tried.</p>
  
  <pre><code>General
  Complete name                    : 429183132058337290450_AutoFF.mp4
  Format                           : MPEG-4
  Format profile                   : Base Media
  Codec ID                         : isom
  File size                        : 10.2 MiB
  Duration                         : 24s 333ms
  Overall bit rate                 : 3 501 Kbps
  
  Video
  ID                               : 1
  Format                           : AVC
  Format/Info                      : Advanced Video Codec
  Format profile                   : High@L4.1
  Format settings, CABAC           : Yes
  Format settings, ReFrames        : 3 frames
  Codec ID                         : avc1
  Codec ID/Info                    : Advanced Video Coding
  Duration                         : 24s 333ms
  Bit rate mode                    : Variable
  Bit rate                         : 3 351 Kbps
  Width                            : 1 024 pixels
  Height                           : 560 pixels
  Display aspect ratio             : 16:9
  Frame rate mode                  : Constant
  Frame rate                       : 30.000 fps
  Color space                      : YUV
  Chroma subsampling               : 4:2:0
  Bit depth                        : 8 bits
  Scan type                        : Progressive
  Bits/(Pixel*Frame)               : 0.195
  Stream size                      : 9.72 MiB (96%)
  Language                         : Japanese
  </code></pre>