It can sound basic, but I see in many forums
-movflags +faststart
-movflags -faststart
-movflags faststart
What is the difference between plus + and minus - or just no sign before the flag ?
What does the signs do ?
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Jintor
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1See https://stackoverflow.com/questions/23419351/ffmpeg-using-movflags-faststart#comment60936769_23440682 – llogan Mar 31 '21 at 22:23
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1@llogan and combining 2 flags, is it better to add a space like this `+faststart +dash` or just no space `+faststart+dash` – Jintor Mar 31 '21 at 23:08
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3No spaces, or else it will assume `+dash` is a separate option or output name. – llogan Mar 31 '21 at 23:17
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Let me just make it an answer here. – Gyan Apr 01 '21 at 04:27
2 Answers
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A + sign indicates that ffmpeg should set the specified value in addition to any values that the MOV/MP4 muxer will automatically set during the course of executing the command.
A - sign indicates that ffmpeg should unset the specified value, useful when one knows if the muxer enables it by default.
Omitting the sign altogether means ffmpeg will reset the flags to their default values, and only toggle the state of faststart.
Gyan
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To put what llogan stated in a comment above but which I missed the first few times I came across this question, if you're specifying multiple MOV flags it's crucial there's no spaces between them:
-movflags +faststart+write_colr
instead of
-movflags +faststart +write_colr
The latter results in an error:
Unable to find a suitable output format for 'write_colr'`
...which I was stuck on for 10 mins before I noticed the comment exchange addressing this above.
Hashim Aziz
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