[FFmpeg-devel] Change 9963 introduces regression - start_time in asf.c

Reimar Döffinger Reimar.Doeffinger
Sun Aug 12 14:07:02 CEST 2007

On Sun, Aug 12, 2007 at 08:44:17PM +1000, Neil Brown wrote:
> And what does it mean for start_time to be AV_NOPTS_VALUE.  Does that
> just mean that the format doesn't contain any explicit start_time
> value.

I means that the value is not known. That might be because we can't know
the value (streaming?), or that we or just too lazy to implement it or

> The documentation says:
>    decoding: pts of the first frame of the stream, in stream time
>    base.
> and while I guess that is better than nothing, it isn't a lot better
> than nothing.

Well, what else to say? It has to be the pts that is associated with the
first packet that is returned when reading from this stream.

> The current code seems to treat start_time and duration as a pair -
> either they are both set or neither are set.  Why does it do that?
> And what will break if break that pairing and have asf set one but not
> the other?

There is no problem whatsoever with setting only one of those, and AFAIK
there are already demuxers using this.

> And how can I be sure that any given patch won't break anything given
> how shallow my understanding still is.  If there a regression test
> suite any where?  When there a so many format, options, variations
> etc - such a thing would seem very useful.

"make tests"

> So anyway, if you can just tell me how start_time is used, it might
> give me enough confidence to submit a patch.

The only use I know out of my head is in MPlayer to display the current
playback position in the progress bar - unfortunately I think that code
is broken since it assumes start_time to be always set.

Reimar D?ffinger

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