FFplay sync ext

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FFplay sync ext

Bouke / VideoToolShed
Hi all,
Seeking a way to slave video playback to an external clock.
(Meaning, jump to specific position and restart playing if the difference between current playback time and external clock is too big.)
Now, FFplay seems pretty simple, but I cannot find anything to control it besides the keyboard. Sending keystrokes seems awkward…

There is a -sync ext option, when I use that the video plays, and I notice a very small speed change in playback.
So what is ‘ext’ ?
Can I input something while playing? Where, what?

Or is FFplay not the tool for this?
(Using python / QT, any other options?)


Bouke

www.VideoToolShed.com
van Oldenbarneveltstraat 33
6512 AS  Nijmegen
+31 6 21817248
To send files, go here:
https://videotoolshed.wetransfer.com/


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Re: FFplay sync ext

Carl Zwanzig
On 11/23/2019 3:48 AM, Bouke / VideoToolShed wrote:
> Seeking a way to slave video playback to an external clock.
> (Meaning, jump to specific position and restart playing if the difference between current playback time and external clock is too big.)

How big is "too big"? A second? Minute? I don't think you're going to get
frame-accuracy.

What do you mean by "playback time" in this context? (The problem may sound
simple, but we're left to make a lot of guesses about what you want to do;
please fill in some details.)


> Or is FFplay not the tool for this?

It may not be. mplayer has a "slave mode" which takes commands, including
seek-to-time (in seconds). So does CasparCG, but that's probably overkill
for a simple player. Remember that any of these will simply jump to that
location in the file and may glitch the picture until a key frame comes along.

Later,

z!
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Re: FFplay sync ext

Bouke / VideoToolShed


> On 23 Nov 2019, at 16:31, Carl Zwanzig <[hidden email]> wrote:
>
> On 11/23/2019 3:48 AM, Bouke / VideoToolShed wrote:
>> Seeking a way to slave video playback to an external clock.
>> (Meaning, jump to specific position and restart playing if the difference between current playback time and external clock is too big.)
>
> How big is "too big"? A second? Minute? I don't think you're going to get frame-accuracy.
>


well, subframe accuracy if possible. I have time in samples from the audio,
Why do you think frame accuracy is not possible?


> What do you mean by "playback time" in this context? (The problem may sound simple, but we're left to make a lot of guesses about what you want to do; please fill in some details.)

I meant, if the player shows a wrong playback time, what can I do then?

>
>
>> Or is FFplay not the tool for this?
>
> It may not be. mplayer has a "slave mode" which takes commands, including seek-to-time (in seconds). So does CasparCG, but that's probably overkill for a simple player. Remember that any of these will simply jump to that location in the file and may glitch the picture until a key frame comes along.
>
> Later,
>
> z!
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Re: FFplay sync ext

Carl Zwanzig
On 11/23/2019 7:41 AM, Bouke / VideoToolShed wrote:
> Why do you think frame accuracy is not possible?

Because you didn't specify the time data available and "clock time" usually
means accuracy in seconds.

Later,

z!

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Re: FFplay sync ext

Bouke / VideoToolShed

> On 23 Nov 2019, at 17:06, Carl Zwanzig <[hidden email]> wrote:
>
> On 11/23/2019 7:41 AM, Bouke / VideoToolShed wrote:
>> Why do you think frame accuracy is not possible?
>
> Because you didn't specify the time data available and "clock time" usually means accuracy in seconds.

This makes no sense whatsoever.
I can provide  the time sample accurate. (Where a sample is 1 / 48000 if needed.)
I asked how to input ‘sync’ data, but have gotten no answer to that.

And,for other operations FFmpeg takes a float as input, and that sub-second accurate.

Bouke

>
> Later,
>
> z!
>
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