[Libav-user] packet flag AV_PKT_FLAG_KEY

Andy Shaules bowljoman at gmail.com
Sat Nov 23 10:07:37 CET 2013

On 11/23/2013 12:05 AM, Don Moir wrote:
> ----- Original Message -----
> From: Andy Shaules
> To: This list is about using libavcodec, libavformat, 
> libavutil,libavdevice and libavfilter.
> Sent: Saturday, November 23, 2013 12:55 AM
> Subject: Re: [Libav-user] packet flag AV_PKT_FLAG_KEY
> On 11/22/2013 7:47 PM, Don Moir wrote:
> >>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.
> >>Is it not a application flag ?
> >>Seems for at least H264 it doesnt have much meaning to application. 
> If the packet dts value is in the stream index_entires then that 
> represents a key frame for sure ( hopefully :)
> >>What if there are no index_entries ? Whats a key packet then and how 
> to determine ?
> >>Just trying to clear up my own confusion with this.
> >For h264, the key frame network abstraction unit of the packet will 
> be of type IDR, instant data refresh.
> >I believe NAL type 5.
> Thanks Andy.
> Dont see that info in a packet. Only thing relevant that changes is 
> the flags member (0 or 1). Now frame may contain additional info after 
> decoding but it's documented that AV_PKT_FLAG_KEY represents a keyframe.
> If it is for internal use, a different flag should have been used the 
> way I see it. So trying to understand what the real intended use of 
> _______________________________________________
> Libav-user mailing list
> Libav-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/libav-user

Imagine H264 at HD resolution with 5 or 6 horizontal slices where the 
key frame only equals one horizontal strip of macro blocks. So yes, it 
may or may not be a full key frame, but it should be an IDR packet.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ffmpeg.org/pipermail/libav-user/attachments/20131123/17da6732/attachment.html>

More information about the Libav-user mailing list