[FFmpeg-user] -movflags +faststart has no effect

Gyan Doshi ffmpeg at gyani.pro
Tue Feb 25 17:04:22 EET 2020

On 25-02-2020 07:47 pm, Ulf Zibis wrote:
> Hi,
> from option -movflags +faststart I expect, that I can start playing the
> video, even the encoding process has not finished yet.
> But this does not work,why?

It's not expected to.  faststart is to allow playback during progressive 
downloaded of a complete and valid MP4 file.

See docs at http://ffmpeg.org/ffmpeg-formats.html#Options-8

> If I encode a video without -movflags +faststart and kill the process
> with Ctrl-C after a while the video surprisingly is playable.

When ffmpeg is sent SIGINT, ffmpeg will attempt to close outputs 
gracefully. For regular MP4 output, this includes flushing the moov atom 
to file. That makes the file playable.


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