Option -omaxfps: limit fps when encoding

Lower-fps content is left alone (NOT aligned to this fps); higher fps
content is decimated to this frame rate.

DOCS/man/en/encode.rst

@@ -45,6 +45,11 @@ You can encode files from one format/codec to another using this facility.
     specified - use --ofps or --oautofps to force CFR encoding in these
     cases.
 
+--omaxfps=<float value>
+    Specifies the minimum distance of adjacent frames (default: 0, which means
+    unset). Content of lower frame rate is not readjusted to this frame rate;
+    content of higher frame rate is decimated to this frame rate.
+
 --oharddup
     If set, the frame rate given by --ofps is attained not by skipping time
     codes, but by duplicating frames (constant frame rate mode).

core/options.c

@@ -709,6 +709,7 @@ const m_option_t mp_opts[] = {
     OPT_STRING("of", encode_output.format, CONF_GLOBAL),
     OPT_STRINGLIST("ofopts*", encode_output.fopts, CONF_GLOBAL),
     OPT_FLOATRANGE("ofps", encode_output.fps, CONF_GLOBAL, 0.0, 1000000.0),
+    OPT_FLOATRANGE("omaxfps", encode_output.maxfps, CONF_GLOBAL, 0.0, 1000000.0),
     OPT_STRING("ovc", encode_output.vcodec, CONF_GLOBAL),
     OPT_STRINGLIST("ovcopts*", encode_output.vopts, CONF_GLOBAL),
     OPT_STRING("oac", encode_output.acodec, CONF_GLOBAL),

core/options.h

@@ -252,6 +252,7 @@ typedef struct MPOpts {
         char *format;
         char **fopts;
         float fps;
+        float maxfps;
         char *vcodec;
         char **vopts;
         char *acodec;

etc/encoding-example-profiles.conf

@@ -153,6 +153,7 @@ profile = enc-f-mp4
 vf-add = dsize=480:360:0:2,scale=w=0:h=0,dsize=-1:-1 # native screen res, letterbox
 ovcopts-add = maxrate=1500k,bufsize=1000k,rc_init_occupancy=900k,refs=1,profile=baseline
 vf-add=noformat=444p,noformat=444p9,noformat=444p10,noformat=422p,noformat=422p9,noformat=422p10
+omaxfps = 30
 
 [enc-to-nok-n900]
 profile-desc = "MP4 for Nokia N900"
@@ -160,6 +161,7 @@ profile = enc-f-mp4
 vf-add = dsize=800:480:0:2,scale=w=0:h=0:noup=1,scale=w=-1:h=-2:noup=1,scale=w=-2:h=-1:noup=1,dsize=-1:-1 # native screen res, letterbox
 ovcopts-add = profile=baseline,level=30,maxrate=10000k,bufsize=10000k,rc_init_occupancy=9000k,refs=5
 vf-add=noformat=444p,noformat=444p9,noformat=444p10,noformat=422p,noformat=422p9,noformat=422p10
+omaxfps = 30
 
 [enc-to-nok-6300]
 profile-desc = "3GP for Nokia 6300"
@@ -186,18 +188,22 @@ profile = enc-f-mp4
 oautofps = yes # iphone supports 30fps max
 ovcopts-add = maxrate=2500k,bufsize=1000k,rc_init_occupancy=900k,level=30,profile=baseline
 vf-add=noformat=444p,noformat=444p9,noformat=444p10,noformat=422p,noformat=422p9,noformat=422p10
+omaxfps = 30
 
 [enc-to-iphone]
 profile-desc = "MP4 for iPhone (480x320)"
 profile = enc-to-iphone-noscale
 vf-add = dsize=480:320:1:2,scale=w=0:h=0,dsize=-1:-1 # panscan
+omaxfps = 30
 
 [enc-to-iphone-4]
 profile-desc = "MP4 for iPhone 4 (960x640)"
 profile = enc-to-iphone-noscale
 vf-add = dsize=960:480:1:2,scale=w=0:h=0,dsize=-1:-1 # panscan
+omaxfps = 30
 
 [enc-to-iphone-5]
 profile-desc = "MP4 for iPhone 5 (1136x640)"
 profile = enc-to-iphone-noscale
 vf-add = dsize=1136:480:1:2,scale=w=0:h=0,dsize=-1:-1 # panscan
+omaxfps = 30

video/out/vo_lavc.c

@@ -48,6 +48,7 @@ struct priv {
     double lastpts;
     int64_t lastipts;
     int64_t lastframeipts;
+    int64_t mindeltapts;
     double expected_next_pts;
     mp_image_t *lastimg;
     int lastimg_wants_osd;
@@ -317,6 +318,11 @@ static void draw_image(struct vo *vo, mp_image_t *mpi)
             vc->worst_time_base = vc->stream->time_base;
             vc->worst_time_base_is_stream = 1;
         }
+        if (ectx->options->maxfps)
+            vc->mindeltapts = ceil(vc->worst_time_base.den /
+                    (vc->worst_time_base.num * ectx->options->maxfps));
+        else
+            vc->mindeltapts = 0;
 
         // NOTE: we use the following "axiom" of av_rescale_q:
         // if time base A is worse than time base B, then
@@ -394,6 +400,16 @@ static void draw_image(struct vo *vo, mp_image_t *mpi)
         vc->lastpts = frameipts * timeunit - encode_lavc_getoffset(ectx, vc->stream);
     }
 
+    // lastipts: pts of last vo frame
+    // frameipts: pts of current vo frame
+    // lastframeipts: pts of last ENCODED frame
+    // now we want to go forward in time until at least lastframeipts + mindeltapts
+    // so let's just assume this frame took place at this time or later
+    if (frameipts >= vc->lastframeipts && frameipts < vc->lastframeipts + vc->mindeltapts) {
+        frameipts = vc->lastframeipts + vc->mindeltapts;
+        vc->lastpts = frameipts * timeunit - encode_lavc_getoffset(ectx, vc->stream);
+    }
+
     if (vc->lastipts != MP_NOPTS_VALUE) {
         frame = avcodec_alloc_frame();