[Ffmpeg-devel] av_seek_frame() units

[Steve Willis]

Nathan Kurz wrote:
> On Wed, Jul 06, 2005 at 12:04:44PM -0700, Ian Gowen wrote:
> 
>>On 7/6/05, Andy Parkins <andyparkins at gmail.com> wrote:
>>
>>>I'm not sure why you would need to do this.  What source for frame_number are
>>>you using - it's not in any of the AV structures.
>>
>>I'm working on a video editing application. If the user wants to
>>preview frame 320, I
>>need it to seek to frame 320, not the nearest keyframe or a frame in
>>the general
>>vicinity of frame 320.
> 
> 
> Not to be too discouraging, but you should also know that seek is
> badly broken for many formats.  It's quite possible that you are doing
> things correctly, but are being bitten by bugs.  If you search  the
> archives from (I think) the end of last year you'll find a fairly
> elaborate test program I wrote to test which formats work.  I had
> submitted it as a regression test, but as it pointed out new bugs
> rather than regressions it wasn't included in the test suite.
> 
> Nathan Kurz
> nate at verse.com
> 
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It sounds like Ian and I are both working on applications that need 
precise frame positioning. In light of what Nathan said above, can 
anyone offer recommendations for the best way to ensure that the user is 
looking at the frame he or she thinks they should be looking at? Is 
there a reliable way to detect when seek has gone wrong ("I expected to 
be looking at the frame for time 13.125 seconds, but I actually got the 
frame for time X...error!")?

In response to my original question a couple of weeks ago, someone 
suggested using a format like MJPEG that treats all frames as keyframes. 
If there is not a more general solution for precicely positioning 
arbitrarily-formatted streams, could someone give me an expert opinion 
on the best format to transcode all input videos into? The videos I am 
dealing with are printed from high speed film (1000 fps) for scientific 
analysis frame-by-frame. I'm looking for a reasonable balance between 
decoding speed and size. Image quality is of course important for seeing 
detail in each frame of interest. Most important is that the frame shown 
is actually correct for the time in question to match up with external 
sensor data, so a format that does not use keyframes would also be 
important.

Thanks,

Steve