lavf: refactor av_read_frame() to make it easier to understand.

libavformat/utils.c

@@ -31,6 +31,7 @@
 #include "libavutil/pixdesc.h"
 #include "metadata.h"
 #include "id3v2.h"
+#include "libavutil/avassert.h"
 #include "libavutil/avstring.h"
 #include "libavutil/mathematics.h"
 #include "libavutil/parseutils.h"
@@ -1248,18 +1249,34 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
     return 0;
 }
 
+static int read_from_packet_buffer(AVFormatContext *s, AVPacket *pkt)
+{
+    AVPacketList *pktl = s->packet_buffer;
+    av_assert0(pktl);
+    *pkt = pktl->pkt;
+    s->packet_buffer = pktl->next;
+    av_freep(&pktl);
+    return 0;
+}
+
 int av_read_frame(AVFormatContext *s, AVPacket *pkt)
 {
     AVPacketList *pktl;
     int eof=0;
     const int genpts= s->flags & AVFMT_FLAG_GENPTS;
 
+    if (!genpts)
+        return s->packet_buffer ? read_from_packet_buffer(s, pkt) :
+                                  read_frame_internal(s, pkt);
+
     for(;;){
+        int ret;
         pktl = s->packet_buffer;
+
         if (pktl) {
             AVPacket *next_pkt= &pktl->pkt;
 
-            if(genpts && next_pkt->dts != AV_NOPTS_VALUE){
+            if (next_pkt->dts != AV_NOPTS_VALUE) {
                 int wrap_bits = s->streams[next_pkt->stream_index]->pts_wrap_bits;
                 while(pktl && next_pkt->pts == AV_NOPTS_VALUE){
                     if(   pktl->pkt.stream_index == next_pkt->stream_index
@@ -1272,33 +1289,24 @@ int av_read_frame(AVFormatContext *s, AVPacket *pkt)
                 pktl = s->packet_buffer;
             }
 
-            if(   next_pkt->pts != AV_NOPTS_VALUE
-               || next_pkt->dts == AV_NOPTS_VALUE
-               || !genpts || eof){
-                /* read packet from packet buffer, if there is data */
-                *pkt = *next_pkt;
-                s->packet_buffer = pktl->next;
-                av_free(pktl);
-                return 0;
-            }
+            /* read packet from packet buffer, if there is data */
+            if (!(next_pkt->pts == AV_NOPTS_VALUE &&
+                  next_pkt->dts != AV_NOPTS_VALUE && !eof))
+                return read_from_packet_buffer(s, pkt);
         }
-        if(genpts){
-            int ret= read_frame_internal(s, pkt);
-            if(ret<0){
-                if(pktl && ret != AVERROR(EAGAIN)){
-                    eof=1;
-                    continue;
-                }else
-                    return ret;
-            }
 
-            if(av_dup_packet(add_to_pktbuf(&s->packet_buffer, pkt,
-                                           &s->packet_buffer_end)) < 0)
-                return AVERROR(ENOMEM);
-        }else{
-            assert(!s->packet_buffer);
-            return read_frame_internal(s, pkt);
+        ret = read_frame_internal(s, pkt);
+        if (ret < 0) {
+            if (pktl && ret != AVERROR(EAGAIN)) {
+                eof = 1;
+                continue;
+            } else
+                return ret;
         }
+
+        if (av_dup_packet(add_to_pktbuf(&s->packet_buffer, pkt,
+                          &s->packet_buffer_end)) < 0)
+            return AVERROR(ENOMEM);
     }
 }