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

[James Zern]

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
-------------- next part --------------
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});
+    }
+
     enccfg.g_w            = avctx->width;
     enccfg.g_h            = avctx->height;
     enccfg.g_timebase.num = avctx->time_base.num;
     enccfg.g_timebase.den = avctx->time_base.den;
     enccfg.g_threads      = avctx->thread_count;
+    enccfg.g_lag_in_frames= FFMIN(avctx->rc_lookahead, 25);  //0-25, avoids init failure
 
     if (avctx->flags & CODEC_FLAG_PASS1)
         enccfg.g_pass = VPX_RC_FIRST_PASS;
@@ -290,6 +300,7 @@ static av_cold int vp8_init(AVCodecConte
     av_log(avctx, AV_LOG_DEBUG, "vpx_codec_control\n");
     codecctl_int(avctx, VP8E_SET_CPUUSED,           cpuused);
     codecctl_int(avctx, VP8E_SET_NOISE_SENSITIVITY, avctx->noise_reduction);
+    codecctl_int(avctx, VP8E_SET_ENABLEAUTOALTREF,  !!(avctx->flags2 & CODEC_FLAG2_ALT_REF));
 
     //provide dummy value to initialize wrapper, values will be updated each _encode()
     vpx_img_wrap(&ctx->rawimg, VPX_IMG_FMT_I420, avctx->width, avctx->height, 1,