avconv: insert extra filters in the same way for both graph inputs and outputs

This will allow using the same code when one filter can be inserted both
on input and output.

avconv_filter.c

@@ -412,14 +412,13 @@ int configure_output_filter(FilterGraph *fg, OutputFilter *ofilter, AVFilterInOu
 static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
                                         AVFilterInOut *in)
 {
-    AVFilterContext *first_filter = in->filter_ctx;
+    AVFilterContext *last_filter;
     const AVFilter *buffer_filt = avfilter_get_by_name("buffer");
     InputStream *ist = ifilter->ist;
     AVRational tb = ist->framerate.num ? av_inv_q(ist->framerate) :
                                          ist->st->time_base;
     AVRational sar;
     char args[255], name[255];
-    int pad_idx = in->pad_idx;
     int ret;
 
     sar = ist->st->sample_aspect_ratio.num ?
@@ -434,6 +433,7 @@ static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
     if ((ret = avfilter_graph_create_filter(&ifilter->filter, buffer_filt, name,
                                             args, NULL, fg->graph)) < 0)
         return ret;
+    last_filter = ifilter->filter;
 
     if (ist->framerate.num) {
         AVFilterContext *setpts;
@@ -446,14 +446,13 @@ static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
                                                 fg->graph)) < 0)
             return ret;
 
-        if ((ret = avfilter_link(setpts, 0, first_filter, pad_idx)) < 0)
+        if ((ret = avfilter_link(last_filter, 0, setpts, 0)) < 0)
             return ret;
 
-        first_filter = setpts;
-        pad_idx = 0;
+        last_filter = setpts;
     }
 
-    if ((ret = avfilter_link(ifilter->filter, 0, first_filter, pad_idx)) < 0)
+    if ((ret = avfilter_link(last_filter, 0, in->filter_ctx, in->pad_idx)) < 0)
         return ret;
     return 0;
 }
@@ -461,10 +460,9 @@ static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
 static int configure_input_audio_filter(FilterGraph *fg, InputFilter *ifilter,
                                         AVFilterInOut *in)
 {
-    AVFilterContext *first_filter = in->filter_ctx;
+    AVFilterContext *last_filter;
     const AVFilter *abuffer_filt = avfilter_get_by_name("abuffer");
     InputStream *ist = ifilter->ist;
-    int pad_idx = in->pad_idx;
     char args[255], name[255];
     int ret;
 
@@ -481,6 +479,7 @@ static int configure_input_audio_filter(FilterGraph *fg, InputFilter *ifilter,
                                             name, args, NULL,
                                             fg->graph)) < 0)
         return ret;
+    last_filter = ifilter->filter;
 
     if (audio_sync_method > 0) {
         AVFilterContext *async;
@@ -503,12 +502,11 @@ static int configure_input_audio_filter(FilterGraph *fg, InputFilter *ifilter,
         if (ret < 0)
             return ret;
 
-        ret = avfilter_link(async, 0, first_filter, pad_idx);
+        ret = avfilter_link(last_filter, 0, async, 0);
         if (ret < 0)
             return ret;
 
-        first_filter = async;
-        pad_idx = 0;
+        last_filter = async;
     }
     if (audio_volume != 256) {
         AVFilterContext *volume;
@@ -526,14 +524,13 @@ static int configure_input_audio_filter(FilterGraph *fg, InputFilter *ifilter,
         if (ret < 0)
             return ret;
 
-        ret = avfilter_link(volume, 0, first_filter, pad_idx);
+        ret = avfilter_link(last_filter, 0, volume, 0);
         if (ret < 0)
             return ret;
 
-        first_filter = volume;
-        pad_idx = 0;
+        last_filter = volume;
     }
-    if ((ret = avfilter_link(ifilter->filter, 0, first_filter, pad_idx)) < 0)
+    if ((ret = avfilter_link(last_filter, 0, in->filter_ctx, in->pad_idx)) < 0)
         return ret;
 
     return 0;