apad: add whole_len and pad_len options.

These options allow padding to a specific length or adding a specific amount if silence.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/af_apad.c

@@ -40,6 +40,8 @@ typedef struct {
     int64_t next_pts;
 
     int packet_size;
+    int64_t pad_len;
+    int64_t whole_len;
 } APadContext;
 
 #define OFFSET(x) offsetof(APadContext, x)
@@ -47,6 +49,8 @@ typedef struct {
 
 static const AVOption apad_options[] = {
     { "packet_size", "set silence packet size", OFFSET(packet_size), AV_OPT_TYPE_INT, { .i64 = 4096 }, 0, INT_MAX, A },
+    { "pad_len",     "number of samples of silence to add",          OFFSET(pad_len),   AV_OPT_TYPE_INT64, { .i64 = 0 }, 0, INT64_MAX, A },
+    { "whole_len",   "target number of samples in the audio stream", OFFSET(whole_len), AV_OPT_TYPE_INT64, { .i64 = 0 }, 0, INT64_MAX, A },
     { NULL },
 };
 
@@ -65,6 +69,11 @@ static av_cold int init(AVFilterContext *ctx, const char *args)
     if ((ret = av_opt_set_from_string(apad, args, NULL, "=", ":")) < 0)
         return ret;
 
+    if (apad->whole_len && apad->pad_len) {
+        av_log(ctx, AV_LOG_ERROR, "Both whole and pad length are set, this is not possible\n");
+        return AVERROR(EINVAL);
+    }
+
     av_opt_free(apad);
 
     return 0;
@@ -74,6 +83,10 @@ static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *frame)
 {
     AVFilterContext *ctx = inlink->dst;
     APadContext *apad = ctx->priv;
+
+    if (apad->whole_len)
+        apad->whole_len -= frame->audio->nb_samples;
+
     apad->next_pts = frame->pts + av_rescale_q(frame->audio->nb_samples, (AVRational){1, inlink->sample_rate}, inlink->time_base);
     return ff_filter_frame(ctx->outputs[0], frame);
 }
@@ -88,7 +101,21 @@ static int request_frame(AVFilterLink *outlink)
 
     if (ret == AVERROR_EOF) {
         int n_out = apad->packet_size;
-        AVFilterBufferRef *outsamplesref = ff_get_audio_buffer(outlink, AV_PERM_WRITE, n_out);
+        AVFilterBufferRef *outsamplesref;
+
+        if (apad->whole_len > 0) {
+            apad->pad_len = apad->whole_len;
+            apad->whole_len = 0;
+        }
+        if (apad->pad_len > 0) {
+            n_out = FFMIN(n_out, apad->pad_len);
+            apad->pad_len -= n_out;
+        }
+
+        if(!n_out)
+            return AVERROR_EOF;
+
+        outsamplesref = ff_get_audio_buffer(outlink, AV_PERM_WRITE, n_out);
         if (!outsamplesref)
             return AVERROR(ENOMEM);