Fix heap overflow with -async.

Fixes issue1666

Originally committed as revision 21390 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -563,6 +563,7 @@ static void do_audio_out(AVFormatContext *s,
 {
     uint8_t *buftmp;
     int64_t audio_out_size, audio_buf_size;
+    int64_t allocated_for_size= size;
 
     int size_out, frame_bytes, ret;
     AVCodecContext *enc= ost->st->codec;
@@ -571,7 +572,8 @@ static void do_audio_out(AVFormatContext *s,
     int isize= av_get_bits_per_sample_format(dec->sample_fmt)/8;
     const int coded_bps = av_get_bits_per_sample(enc->codec->id);
 
-    audio_buf_size= (size + isize*dec->channels - 1) / (isize*dec->channels);
+need_realloc:
+    audio_buf_size= (allocated_for_size + isize*dec->channels - 1) / (isize*dec->channels);
     audio_buf_size= (audio_buf_size*enc->sample_rate + dec->sample_rate) / dec->sample_rate;
     audio_buf_size= audio_buf_size*2 + 10000; //safety factors for the deprecated resampling API
     audio_buf_size*= osize*enc->channels;
@@ -649,10 +651,11 @@ static void do_audio_out(AVFormatContext *s,
                     static uint8_t *input_tmp= NULL;
                     input_tmp= av_realloc(input_tmp, byte_delta + size);
 
-                    if(byte_delta + size <= MAX_AUDIO_PACKET_SIZE)
+                    if(byte_delta > allocated_for_size - size){
+                        allocated_for_size= byte_delta + (int64_t)size;
+                        goto need_realloc;
+                    }
                     ist->is_start=0;
-                    else
-                        byte_delta= MAX_AUDIO_PACKET_SIZE - size;
 
                     memset(input_tmp, 0, byte_delta);
                     memcpy(input_tmp + byte_delta, buf, size);