[vlc-devel] [PATCH v2] Reset p_context->skip_frame when done seeking

[Marc Aldorasi]

On Tue, Aug 20, 2019 at 12:59 AM Steve Lhomme <robux4 at ycbcr.xyz> wrote:
>
>
>
> On 2019-08-20 3:26, Marc Aldorasi wrote:
> > On Mon, Aug 19, 2019 at 8:39 AM Steve Lhomme <robux4 at ycbcr.xyz> wrote:
> >>
> >> Hi,
> >>
> >> On 2019-08-06 5:39, Marc Aldorasi wrote:
> >>> Previously, if p_sys->b_hurry_up was false and we weren't seeking, the
> >>> value of p_context->skip_frame would not be modified.  This means that
> >>> if we started seeking we would set p_context->skip_frame to
> >>> AVDISCARD_NONREF, and then when we finished seeking we wouldn't change
> >>> p_context->skip_frame and it would still be skipping non-reference
> >>> frames, causing choppy playback.  This patch resets
> >>> p_context->skip_frame when we're not seeking so playback is smooth.
> >>
> >> The p_context->skip_frame should indeed be reset once seeking is done
> >> and that's currently not the case if b_hurry_up is false. But it should
> >> reset it to AVDISCARD_DEFAULT which is the value that is used when
> >> p_sys->b_hurry_up is false, not the p_sys->i_skip_frame value. Otherwise
> >> that makes the "avcodec-hurry-up" option useless since it would always
> >> be applied.

While writing this patch, I discovered that this is not the case.
p_context->skip_frame is initialized to the value of
avcodec-skip-frame without regard to the value of avcodec-hurry-up
(see video.c:583).  So there are 2 options:

1. Respect the value of avcodec-skip-frame unconditionally (the
current behavior when not seeking), making avcodec-hurry-up only
control filtering early blocks.
2. Respect the value of avcodec-skip-frame only when avcodec-hurry-up
is set, causing it to enable both frame skipping and filtering early
blocks, and use AVDISCARD_DEFAULT when avcodec-hurry-up is not set.

Which of these is the preferred behavior?  I'm leaning towards 1, but
both make sense to me.

> >
> > I'm a bit confused by this.  In response to the last patch you wrote
> >
> >> It's a good idea to reset the skip_frame once seeking is done, but it
> >> should revert to "p_sys->i_skip_frame" so that it respects the
> >> "avcodec-skip-frame" variable.
> >
> > which I took to mean that it should always be respecting
> > avcodec-skip-frame.  If I follow the latest suggestion, I'm concerned it
> > contradicts the previous suggestion.
> >
> >> By default the "avcodec-hurry-up" option is true. That means people who
> >> set it to false really don't want to skip more than non-ref frames.
> >>
> >> On the other hand to achieve that they could also use
> >> --avcodec-skip-frame=1 and it would have the same effect.
> >>
> >> So if you want to go that way you should also remove (make obsolete) the
> >> avcodec-hurry-up option.
> >
> > The avcodec-hurry-up option still guards the call to
> > filter_earlydropped_blocks, so I'd prefer not to go that way.
>
> Ah yes, I missed that part. So never mind, we still keep both options.
> We just need to reset properly p_context->skip_frame in both modes then.
>
> >> By the way, the second part of this test in the current code is useless,
> >> FRAMEDRO_NONREF is never used/set in the code:
> >>
> >>     if( !b_need_output_picture || p_sys->framedrop == FRAMEDROP_NONREF )
> >
> > Good catch, I'll remove that.
> >
> >>> ---
> >>>    modules/codec/avcodec/video.c | 14 ++++++--------
> >>>    1 file changed, 6 insertions(+), 8 deletions(-)
> >>>
> >>> diff --git a/modules/codec/avcodec/video.c b/modules/codec/avcodec/video.c
> >>> index 2232b7a291..d9be9d4a61 100644
> >>> --- a/modules/codec/avcodec/video.c
> >>> +++ b/modules/codec/avcodec/video.c
> >>> @@ -1031,15 +1031,13 @@ static int DecodeBlock( decoder_t *p_dec, block_t **pp_block )
> >>>        else
> >>>            b_need_output_picture = false;
> >>>
> >>> -    /* Change skip_frame config only if hurry_up is enabled */
> >>> -    if( p_sys->b_hurry_up )
> >>> -    {
> >>> -        p_context->skip_frame = p_sys->i_skip_frame;
> >>> +    p_context->skip_frame = p_sys->i_skip_frame;
> >>>
> >>> -        /* Check also if we should/can drop the block and move to next block
> >>> -            as trying to catchup the speed*/
> >>> -        if( p_dec->b_frame_drop_allowed )
> >>> -            p_block = filter_earlydropped_blocks( p_dec, p_block );
> >>> +    /* Check if we should/can drop the block and move to the next block
> >>> +       to try to catchup */
> >>> +    if( p_sys->b_hurry_up && p_dec->b_frame_drop_allowed )
> >>> +    {
> >>> +        p_block = filter_earlydropped_blocks( p_dec, p_block );
> >>>        }
> >>>
> >>>        if( !b_need_output_picture || p_sys->framedrop == FRAMEDROP_NONREF )
> >>> --
> >>> 2.22.0
> >>>
> > _______________________________________________
> > vlc-devel mailing list
> > To unsubscribe or modify your subscription options:
> > https://mailman.videolan.org/listinfo/vlc-devel
> >
> _______________________________________________
> vlc-devel mailing list
> To unsubscribe or modify your subscription options:
> https://mailman.videolan.org/listinfo/vlc-devel