[FFmpeg-devel] [PATCH] Avoid a few shifts on each frame while decoding mpeg audio.

[Clément Bœsch]

Hi,

The MPEG audio parser seems to do a few useless shifts each time a new
frame is sent for feeding; this patch avoids this (one read instead of 4
shifts). I ran the fate tests locally and it seems it didn't break
anything.

Also, I don't understand the header_count field (in use a few lines below)
so it may be wise to check if it is not related to what I tried to
achieve.

Regards,

-- 
Cl?ment B.
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>From beb7d21224596d98dd3eebca5fef43c74da5c1ad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= <ubitux at gmail.com>
Date: Sun, 16 Jan 2011 21:43:16 +0100
Subject: [PATCH] Avoid a few shifts on each frame while decoding mpeg audio.

---
 libavcodec/mpegaudio_parser.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/libavcodec/mpegaudio_parser.c b/libavcodec/mpegaudio_parser.c
index 6d7ab8a..5ced648 100644
--- a/libavcodec/mpegaudio_parser.c
+++ b/libavcodec/mpegaudio_parser.c
@@ -103,7 +103,11 @@ static int mpegaudio_parse(AVCodecParserContext *s1,
             while(i<buf_size){
                 int ret, sr, channels, bit_rate, frame_size;
 
-                state= (state<<8) + buf[i++];
+                if (i == 0 && buf_size >= 4) {
+                    state = AV_RB32(buf);
+                    i += 4;
+                } else
+                    state = (state<<8) + buf[i++];
 
                 ret = ff_mpa_decode_header(avctx, state, &sr, &channels, &frame_size, &bit_rate);
                 if (ret < 4) {
-- 
1.7.3.5

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