[MPlayer-users] Stepping frame by frame

[Corey Hickey]

Loren Merritt wrote:
> 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.

Huh. Interesting. I wasn't able to test it before, but I am now. My 
desktop machine has an sblive and onboard NVidia CK8S audio (using the 
snd-intel8x0 driver). For both the sblive and nvidia, I can reproduce 
the problem with -ao null and -ao oss, but not with -ao alsa. Openal and 
sdl use alsa on my machine, so no problem there either.

On my laptop, however, -ao alsa has the problem as well. It has an Intel 
82801CA-ICH3 chipset, also using snd-intel8x0.

-Corey