[FFmpeg-devel] Question: Null and Nonref frames in indeo3

[Kostya]

On Fri, Sep 11, 2009 at 03:14:15PM +0200, Maxim wrote:
> Hi guys,
> 
> I'm about to submit an updated patch for indeo3 replacement. My last
> technical question is about how to handle the following frame types:
> 
> - NULL or SYNC frames don't contain any picture. Those are needed for
> the synchronization purposes because the .AVI container doesn't support
> variable frame rate. The decoder usually sends the previous picture
> again if such a frame is encountered.
> 
> - NONREF or DROPPABLE INTER frames act just like the normal INTER frames
> with exception those can be discarded easily without damaging the whole
> video sequence. Thus a video can be displayed at reduced frame rate if
> there no enough decoding resources available...
> 
> Now my questions:
> - which action should be taken in order to inform the ffmpeg about the
> above mentioned frames (setting a flag, send the previously decoded
> frame, do nothing)?

Nothing

> - what should the decoder do in the case there it must hurry up: check a
> special flag and skip decoding of the NONREF frames, decode fewer planes?

just don't decode them - many decoders just search for conditions like
(avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==FF_B_TYPE)
(avctx->hurry_up && s->pict_type==FF_B_TYPE)
(avctx->hurry_up>=5)

> - how ffmpeg reacts on such frames (discard them if needed, ignore)?
> 
> Thanks in advance
> Best regards
> Maxim