[FFmpeg-devel] [PATCH] libvpx: alt reference frame / lag

[Michael Niedermayer]

On Wed, Jun 09, 2010 at 12:08:59PM -0400, James Zern wrote:
> On Tue, Jun 8, 2010 at 22:19, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Jun 08, 2010 at 06:44:42PM -0400, James Zern wrote:
> >> The attached adds altref to flags2 and uses rc_lookahead for
> >> g_lag_in_frames mapping.
> >> Alternate reference frames are currently only produced in 2-pass.
> >> Further description outside of the API docs [1]. I'm ignoring the alt.
> >> ref. noise reduction settings for this pass.
> >>
> >> [1]: http://www.webmproject.org/tools/encoder-parameters/#5_the_alternate_or_constructed_reference_frame
> >
> >> ?avcodec.h ? | ? ?5 +++--
> >> ?libvpxenc.c | ? 11 +++++++++++
> >> ?options.c ? | ? ?1 +
> >> ?3 files changed, 15 insertions(+), 2 deletions(-)
> >> 5c3078a90d9d169ab2ceae1622311bec825e8ba9 ?libvpxenc-altref__lag.diff
> >> Index: libavcodec/options.c
> >> ===================================================================
> >> --- libavcodec/options.c ? ? ?(revision 23540)
> >> +++ libavcodec/options.c ? ? ?(working copy)
> >> @@ -414,6 +414,7 @@ static const AVOption options[]={
> >> ?{"intra_refresh", "use periodic insertion of intra blocks instead of keyframes", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_INTRA_REFRESH, INT_MIN, INT_MAX, V|E, "flags2"},
> >> ?{"crf_max", "in crf mode, prevents vbv from lowering quality beyond this point", OFFSET(crf_max), FF_OPT_TYPE_FLOAT, DEFAULT, 0, 51, V|E},
> >> ?{"log_level_offset", "set the log level offset", OFFSET(log_level_offset), FF_OPT_TYPE_INT, 0, INT_MIN, INT_MAX },
> >> +{"altref", "enable use of alternate reference frames (VP8/2-pass only)", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_ALT_REF, INT_MIN, INT_MAX, V|E, "flags2"},
> >> ?{NULL},
> >> ?};
> >>
> >> Index: libavcodec/avcodec.h
> >> ===================================================================
> >> --- libavcodec/avcodec.h ? ? ?(revision 23540)
> >> +++ libavcodec/avcodec.h ? ? ?(working copy)
> >> @@ -30,8 +30,8 @@
> >> ?#include "libavutil/avutil.h"
> >>
> >> ?#define LIBAVCODEC_VERSION_MAJOR 52
> >> -#define LIBAVCODEC_VERSION_MINOR 75
> >> -#define LIBAVCODEC_VERSION_MICRO ?1
> >> +#define LIBAVCODEC_VERSION_MINOR 76
> >> +#define LIBAVCODEC_VERSION_MICRO ?0
> >>
> >> ?#define LIBAVCODEC_VERSION_INT ?AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
> >> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? LIBAVCODEC_VERSION_MINOR, \
> >> @@ -600,6 +600,7 @@ typedef struct RcOverride{
> >> ?#define CODEC_FLAG2_PSY ? ? ? ? ? 0x00080000 ///< Use psycho visual optimizations.
> >> ?#define CODEC_FLAG2_SSIM ? ? ? ? ?0x00100000 ///< Compute SSIM during encoding, error[] values are undefined.
> >> ?#define CODEC_FLAG2_INTRA_REFRESH 0x00200000 ///< Use periodic insertion of intra blocks instead of keyframes.
> >> +#define CODEC_FLAG2_ALT_REF ? ? ? 0x00400000 ///< Allow encoder to insert alternate reference frames (VP8 only)
> >>
> >> ?/* Unsupported options :
> >> ? * ? ? ? ? ? ? ?Syntax Arithmetic coding (SAC)
> >> Index: libavcodec/libvpxenc.c
> >> ===================================================================
> >> --- libavcodec/libvpxenc.c ? ?(revision 23540)
> >> +++ libavcodec/libvpxenc.c ? ?(working copy)
> >> @@ -218,11 +218,21 @@ static av_cold int vp8_init(AVCodecConte
> >> ? ? ?}
> >> ? ? ?dump_enc_cfg(avctx, &enccfg);
> >>
> >> + ? ?/* With altref set an additional frame at the same pts may be produced.
> >> + ? ? ? Increasing the time_base gives the library a window to place these frames
> >> + ? ? ? ensuring strictly increasing timestamps. */
> >> + ? ?if (avctx->flags2 & CODEC_FLAG2_ALT_REF) {
> >> + ? ? ? ?avctx->ticks_per_frame = 2;
> >> + ? ? ? ?avctx->time_base ? ? ? = av_mul_q(avctx->time_base,
> >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?(AVRational){1, avctx->ticks_per_frame});
> >> + ? ?}
> >
> > this looks and sounds wrong
> > the way divx/xvid packed b frames are handled is much saner
> >
> I'll have to have a closer look at that. From what I remember, these
> were flagged within the container with each frame having a new header
> to allow the frames to be broken up by the decoder correct?

the primarely relevant part is that it does not have more frames at container
level than there are output by the decoder.
having the number of frames input in the decoder differ from the output could
cause some problems. Similarly for the encoder. Its likely not unsolveable
if its neccessary but as this is not common it likely would break a few
applications.
besides strictly speaking, frames that are not presented to the user have no
presentation time

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
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