examples/muxing: honour distinction between encoder PTS timebase and stream timebase

Fix PTS set on the frame when encoding, which must be specified in the
encoder timebase or this will confuse the encoder.

When muxing the packet, the PTS/DTS generated by the encoder is then
rescaled to the stream timebase.

doc/examples/muxing.c

@@ -427,6 +427,10 @@ static void write_video_frame(AVFormatContext *oc, AVStream *st)
         /* If size is zero, it means the image was buffered. */
 
         if (!ret && got_packet && pkt.size) {
+            /* rescale output packet timestamp values from codec to stream timebase */
+            pkt.pts = av_rescale_q_rnd(pkt.pts, c->time_base, st->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
+            pkt.dts = av_rescale_q_rnd(pkt.dts, c->time_base, st->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
+            pkt.duration = av_rescale_q(pkt.duration, c->time_base, st->time_base);
             pkt.stream_index = st->index;
 
             /* Write the compressed frame to the media file. */
@@ -545,7 +549,7 @@ int main(int argc, char **argv)
             write_audio_frame(oc, audio_st);
         } else {
             write_video_frame(oc, video_st);
-            frame->pts += av_rescale_q(1, video_st->codec->time_base, video_st->time_base);
+            frame->pts++;
         }
     }