[Libav-user] packet flag AV_PKT_FLAG_KEY

Don Moir donmoir at comcast.net
Wed Dec 4 13:41:39 CET 2013

----- Original Message ----- 
From: "Carl Eugen Hoyos" <cehoyos at ag.or.at>
To: <libav-user at ffmpeg.org>
Sent: Tuesday, December 10, 2013 6:12 PM
Subject: Re: [Libav-user] packet flag AV_PKT_FLAG_KEY

> Don Moir <donmoir at ...> writes:
>> Not sure what AV_PKT_FLAG_KEY is supposed to mean.
>> The assumption to me early on is it represented a key
>> frame but not necessarily.
> Apart from the fact that I simply don't understand the
> second sentence:

Hard to understand is right and still tring to understand.

> What is missing here imo is what is unclear in your opinion
> about the documentation (or for which input stream the
> documentation does not match the behaviour).
> Note that valid H.264 streams do not necessarily contain
> keyframes and therefore do not necessarily contain packets
> with this flag set.
> Carl Eugen

Yes I understand about H.264. The confusion is when there are known key frame index_entries and these do represent at least a start 
point for a key frame. Now seems AV_PKT_FLAG_KEY should dovetail with those entries but it does not.

If you look around some you find confusion about the usage of AV_PKT_FLAG_KEY. If this is used internally for some special case, 
then IMO another flag should have been used. The intent of the flag is just not documented well. Ideally I think it should mark the 
start of a key frame and at least dovetail with index_entries but I am sure it goes deeper than that. 

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