avconv: fix -frames for video encoders with delay.

Frames must be counted when they are passed to the encoder, not when
they come out.

Fixes Bug 202.

avconv.c

@@ -875,6 +875,19 @@ static void write_frame(AVFormatContext *s, AVPacket *pkt, OutputStream *ost)
     AVCodecContext          *avctx = ost->st->codec;
     int ret;
 
+    /*
+     * Audio encoders may split the packets --  #frames in != #packets out.
+     * But there is no reordering, so we can limit the number of output packets
+     * by simply dropping them here.
+     * Counting encoded video frames needs to be done separately because of
+     * reordering, see do_video_out()
+     */
+    if (!(avctx->codec_type == AVMEDIA_TYPE_VIDEO && avctx->codec)) {
+        if (ost->frame_number >= ost->max_frames)
+            return;
+        ost->frame_number++;
+    }
+
     while (bsfc) {
         AVPacket new_pkt = *pkt;
         int a = av_bitstream_filter_filter(bsfc, avctx, NULL,
@@ -902,7 +915,6 @@ static void write_frame(AVFormatContext *s, AVPacket *pkt, OutputStream *ost)
         print_error("av_interleaved_write_frame()", ret);
         exit_program(1);
     }
-    ost->frame_number++;
 }
 
 static void generate_silence(uint8_t* buf, enum AVSampleFormat sample_fmt, size_t size)
@@ -1450,6 +1462,12 @@ static void do_video_out(AVFormatContext *s,
             }
         }
         ost->sync_opts++;
+        /*
+         * For video, number of frames in == number of packets out.
+         * But there may be reordering, so we can't throw away frames on encoder
+         * flush, we need to limit them here, before they go into encoder.
+         */
+        ost->frame_number++;
     }
 }