[MPlayer-users] Stepping frame by frame

[Loren Merritt]

On Tue, 14 Nov 2006, Corey Hickey wrote:
> Pepe wrote:
>> When I use the "." key to step forward frame by frame, then when I press 
>> another key to go back to playback, the video accelerates a lot, just like 
>> it wanted to go inmediately to the place it should be playing if I didn't 
>> pause the video.
>> 
>> Isn't this a bug?
>> 
>> I'm using MPlayer 1.0rc1-3.3.4 but this happened with all previous versions 
>> I used before.
>
> I've never seen this before. My gut response is that it might have something 
> to do with your audio driver. Does it happen when you add '-ao null'?
>
> If the problem doesn't manifest with '-ao null, then try other audio outputs 
> your machine might support. You didn't say what operating system you're 
> using, but ones that might work under Linux are:
> -ao alsa
> -ao oss
> -ao sdl
> -ao esd
> -ao arts
>
> If you don't have any luck there, then you'd better read the bug reporting 
> guidelines in the MPlayer documentation and submit a full bug report.

It is related to audio sync, but I doubt it's driver specific.
MPlayer sends a bunch of audio samples to the card/driver's buffer. Then 
when you start playing (including unpause aftern each frame in framestep), 
MPlayer discards the contents of the buffer and sends the next buffer-full.
So the audio stream advances by the audio buffer size, while the video 
stream advances by one frame.

--Loren Merritt