alsa: fix timefilter usage.

The period argument is supposed to be the number of samples since
the last update.

libavdevice/alsa-audio-dec.c

@@ -123,7 +123,8 @@ static int audio_read_packet(AVFormatContext *s1, AVPacket *pkt)
     dts = av_gettime();
     snd_pcm_delay(s->h, &delay);
     dts -= av_rescale(delay + res, 1000000, s->sample_rate);
-    pkt->pts = ff_timefilter_update(s->timefilter, dts, res);
+    pkt->pts = ff_timefilter_update(s->timefilter, dts, s->last_period);
+    s->last_period = res;
 
     pkt->size = res * s->frame_size;
 

libavdevice/alsa-audio.h

@@ -52,6 +52,7 @@ typedef struct {
     int period_size; ///< preferred size for reads and writes, in frames
     int sample_rate; ///< sample rate set by user
     int channels;    ///< number of channels set by user
+    int last_period;
     TimeFilter *timefilter;
     void (*reorder_func)(const void *, void *, int);
     void *reorder_buf;