[Libav-user] Seeking, timestamps, AVFrame, AVStream

James Board jpboard2 at yahoo.com
Tue Sep 17 21:36:33 CEST 2013

>>Okay, that's helpful. But then how and where and by what program is 
>>timebase calculated?  Do the ffmpeg tools calculate it?  I don't see 
>>how they can.  They'd have to look at every frame in the video and
>>that could take a very long time.
>You should know that video formats reserve some space for metadata. And a portion is dedicated to describe track properties like >VBR/CBR, total time length and so on.
>FFmpeg relies on those metadata to initiate everything but then can recompute some on the fly, some other tools allows to actually >calculate those track metrics directly from track content, it's safer but slower of course.

Let's say my input file is 500 GB and was generated by my capture card.  Robert
said the timebase member in ffmpeg structs hold the maximum granularity of all the timestamps.
I'm wondering how that can be true.  It would take a very long time for ffmpeg to read
500 GB of data to figure out the maximum granularity of all timestamps, and that would
definitely be noticeable.  Something else must happen.
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