media: fix wrong framerate emulation timing

A regression introduced by commit 88405c00 causes
framerate emulation not using the correct timing.
milliseconds was wrongly used in place of microseconds.
This patch changes this fact.

Change-Id: I29453582ce4f0a8f34838caea4a2ee9be5592dbe
Tuleap: #914

src/media/media_decoder.cpp

@@ -327,7 +327,7 @@ MediaDecoder::decode(VideoFrame& result)
             auto target = startTime_ + static_cast<std::int64_t>(frame_time.real() * 1e6);
             auto now = av_gettime();
             if (target > now) {
-                std::this_thread::sleep_for(std::chrono::milliseconds(target - now));
+                std::this_thread::sleep_for(std::chrono::microseconds(target - now));
             }
         }
         return Status::FrameFinished;
@@ -378,7 +378,7 @@ MediaDecoder::decode(const AudioFrame& decodedFrame)
             auto target = startTime_ + static_cast<std::int64_t>(frame_time.real() * 1e6);
             auto now = av_gettime();
             if (target > now) {
-                std::this_thread::sleep_for(std::chrono::milliseconds(target - now));
+                std::this_thread::sleep_for(std::chrono::microseconds(target - now));
             }
         }
         return Status::FrameFinished;