avcodec/libvpxenc: Adds support for constant quality mode in VP9.

Changes in the parameter mapping for libvpx to support the constant
quality mode in VP9. The assumption in the patch is that if crf is
provided but bitrate is 0, then the 'constant quality' mode of VP9
is used. However if both are present, the 'constrained quality' mode
is used as before.
Reviewed-by: James Zern <jzern@google.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libvpxenc.c

@@ -302,14 +302,22 @@ static av_cold int vpx_init(AVCodecContext *avctx,
         enccfg.g_pass = VPX_RC_ONE_PASS;
 
     if (avctx->rc_min_rate == avctx->rc_max_rate &&
-        avctx->rc_min_rate == avctx->bit_rate && avctx->bit_rate)
+        avctx->rc_min_rate == avctx->bit_rate && avctx->bit_rate) {
         enccfg.rc_end_usage = VPX_CBR;
-    else if (ctx->crf)
+    } else if (ctx->crf >= 0) {
         enccfg.rc_end_usage = VPX_CQ;
+#if CONFIG_LIBVPX_VP9_ENCODER
+        if (!avctx->bit_rate && avctx->codec_id == AV_CODEC_ID_VP9)
+            enccfg.rc_end_usage = VPX_Q;
+#endif
+    }
 
     if (avctx->bit_rate) {
         enccfg.rc_target_bitrate = av_rescale_rnd(avctx->bit_rate, 1, 1000,
                                                   AV_ROUND_NEAR_INF);
+#if CONFIG_LIBVPX_VP9_ENCODER
+    } else if (enccfg.rc_end_usage == VPX_Q) {
+#endif
     } else {
         if (enccfg.rc_end_usage == VPX_CQ) {
             enccfg.rc_target_bitrate = 1000000;
@@ -326,7 +334,11 @@ static av_cold int vpx_init(AVCodecContext *avctx,
     if (avctx->qmax >= 0)
         enccfg.rc_max_quantizer = avctx->qmax;
 
-    if (enccfg.rc_end_usage == VPX_CQ) {
+    if (enccfg.rc_end_usage == VPX_CQ
+#if CONFIG_LIBVPX_VP9_ENCODER
+        || enccfg.rc_end_usage == VPX_Q
+#endif
+        ) {
         if (ctx->crf < enccfg.rc_min_quantizer || ctx->crf > enccfg.rc_max_quantizer) {
                 av_log(avctx, AV_LOG_ERROR,
                        "CQ level must be between minimum and maximum quantizer value (%d-%d)\n",
@@ -432,6 +444,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
     if (avctx->codec_id == AV_CODEC_ID_VP8)
         codecctl_int(avctx, VP8E_SET_TOKEN_PARTITIONS,  av_log2(avctx->slices));
     codecctl_int(avctx, VP8E_SET_STATIC_THRESHOLD,  avctx->mb_threshold);
+    if (ctx->crf >= 0)
         codecctl_int(avctx, VP8E_SET_CQ_LEVEL,          ctx->crf);
     if (ctx->max_intra_rate >= 0)
         codecctl_int(avctx, VP8E_SET_MAX_INTRA_BITRATE_PCT, ctx->max_intra_rate);
@@ -779,7 +792,7 @@ static int vp8_encode(AVCodecContext *avctx, AVPacket *pkt,
                          "by the bool decoder, meaning that partitions can be decoded even " \
                          "though earlier partitions have been lost. Note that intra predicition" \
                          " is still done over the partition boundary.",       0, AV_OPT_TYPE_CONST, {.i64 = VPX_ERROR_RESILIENT_PARTITIONS}, 0, 0, VE, "er"}, \
-    { "crf",              "Select the quality for constant quality mode", offsetof(VP8Context, crf), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 63, VE }, \
+    { "crf",              "Select the quality for constant quality mode", offsetof(VP8Context, crf), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 63, VE }, \
 
 #define LEGACY_OPTIONS \
     {"speed", "", offsetof(VP8Context, cpu_used), AV_OPT_TYPE_INT, {.i64 = 1}, -16, 16, VE}, \