[FFmpeg-devel] [PATCH v2 1/4] lavc/aac_ac3_parser: improve the raw AAC file bit rate calculation

[Jun Zhao]

From: Jun Zhao <barryjzhao at tencent.com>

Now we just use one ADTS raw frame to calculate the bit rate, it's
lead to a larger error when get the duration from bit rate, the
improvement cumulate Nth ADTS frames to get the average bit rate.

e,g used the command get the duration like:
ffprobe -show_entries format=duration -i fate-suite/aac/foo.aac

before this improvement dump the duration=2.173935
after this improvement  dump the duration=1.979267

in fact, the real duration can be get by command like:
ffmpeg -i fate-suite/aac/foo.aac -f null /dev/null with time=00:00:01.97

Also update the fate-adtstoasc_ticket3715.

Signed-off-by: Jun Zhao <barryjzhao at tencent.com>
---
 libavcodec/aac_ac3_parser.c         | 9 +++++++--
 libavcodec/aac_ac3_parser.h         | 2 ++
 tests/ref/fate/adtstoasc_ticket3715 | 2 +-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/libavcodec/aac_ac3_parser.c b/libavcodec/aac_ac3_parser.c
index 54e4598..0746798 100644
--- a/libavcodec/aac_ac3_parser.c
+++ b/libavcodec/aac_ac3_parser.c
@@ -97,8 +97,13 @@ get_next:
             avctx->audio_service_type = s->service_type;
         }
 
-        if (avctx->codec_id != AV_CODEC_ID_EAC3)
-            avctx->bit_rate = s->bit_rate;
+        /* Calculate the average bit rate */
+        s->frame_number++;
+        if (avctx->codec_id != AV_CODEC_ID_EAC3) {
+            avctx->bit_rate =
+                (s->last_bit_rate * (s->frame_number -1) + s->bit_rate)/s->frame_number;
+            s->last_bit_rate = avctx->bit_rate;
+        }
     }
 
     return i;
diff --git a/libavcodec/aac_ac3_parser.h b/libavcodec/aac_ac3_parser.h
index c2506a5..b04041f 100644
--- a/libavcodec/aac_ac3_parser.h
+++ b/libavcodec/aac_ac3_parser.h
@@ -55,6 +55,8 @@ typedef struct AACAC3ParseContext {
     uint64_t state;
 
     int need_next_header;
+    int frame_number;
+    int last_bit_rate;
     enum AVCodecID codec_id;
 } AACAC3ParseContext;
 
diff --git a/tests/ref/fate/adtstoasc_ticket3715 b/tests/ref/fate/adtstoasc_ticket3715
index 49fa3eb..3b473ee 100644
--- a/tests/ref/fate/adtstoasc_ticket3715
+++ b/tests/ref/fate/adtstoasc_ticket3715
@@ -1,4 +1,4 @@
-4110be924e21846d0e174fac679b062e *tests/data/fate/adtstoasc_ticket3715.mov
+3e63cbb6bb6ec756d79fab2632fef305 *tests/data/fate/adtstoasc_ticket3715.mov
 33324 tests/data/fate/adtstoasc_ticket3715.mov
 #extradata 0:        2, 0x00340022
 #tb 0: 1/44100
-- 
2.7.4