From: Andre Noll <maan@systemlinux.org>
Date: Sun, 15 Mar 2009 17:59:48 +0000 (+0100)
Subject: mp3: Avoid rounding errors during bitrate calculation.
X-Git-Tag: v0.3.4~31
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=53538a87930479923ae574e30bfbf2cc1c997b29

mp3: Avoid rounding errors during bitrate calculation.

Just add up the bitrates of all frames and divide by the number
of frames afterwards. By using uint64_t for the sum, we should
be safe wrt. overflows.
---

diff --git a/mp3_afh.c b/mp3_afh.c
index 932a7721..8eec436c 100644
--- a/mp3_afh.c
+++ b/mp3_afh.c
@@ -394,7 +394,7 @@ static int find_valid_start(unsigned char *map, size_t numbytes, off_t *fpos,
 static int mp3_read_info(unsigned char *map, size_t numbytes, int fd,
 		struct afh_info *afhi)
 {
-	long freq_avg = 0, br_avg = 0;
+	uint64_t freq_sum = 0, br_sum = 0;
 	int ret, len = 0, old_br = -1, vbr = 0;
 	struct timeval total_time = {0, 0};
 	unsigned chunk_table_size = 1000; /* gets increased on demand */
@@ -406,7 +406,7 @@ static int mp3_read_info(unsigned char *map, size_t numbytes, int fd,
 	afhi->chunk_table = para_malloc(chunk_table_size * sizeof(uint32_t));
 	taginfo = mp3_get_id3(map, numbytes, fd);
 	while (1) {
-		unsigned long freq, br, fl;
+		int freq, br, fl;
 		struct timeval tmp, cct; /* current chunk time */
 		fpos += len;
 		len = find_valid_start(map, numbytes, &fpos, &header);
@@ -429,35 +429,25 @@ static int mp3_read_info(unsigned char *map, size_t numbytes, int fd,
 		tv_divide(br * 125, &tmp, &cct);
 		tv_add(&cct, &total_time, &tmp);
 		total_time = tmp;
-		//PARA_DEBUG_LOG("%s: br: %d, freq: %d, fl: %d, cct: %lu\n", __func__, br, freq, fl, cct.tv_usec);
 		if (afhi->chunks_total >= chunk_table_size) {
 			chunk_table_size *= 2;
 			afhi->chunk_table = para_realloc(afhi->chunk_table,
 				chunk_table_size * sizeof(uint32_t));
 		}
 		afhi->chunk_table[afhi->chunks_total] = fpos;
-//		if (afhi->chunks_total < 10 || !(afhi->chunks_total % 1000))
-//			PARA_INFO_LOG("chunk #%lu: %zd\n", afhi->chunks_total,
-//				afhi->chunk_table[afhi->chunks_total]);
 		afhi->chunks_total++;
-		if (afhi->chunks_total == 1) {
-			freq_avg = freq;
-			br_avg = br;
-			old_br = br;
-			continue;
-		}
-		freq_avg += ((long)freq - freq_avg) / ((long)afhi->chunks_total + 1);
-		br_avg += ((long)br - br_avg) / ((long)afhi->chunks_total + 1);
-		if (old_br != br)
+		freq_sum += freq;
+		br_sum += br;
+		if (afhi->chunks_total != 1 && old_br != br)
 			vbr = 1;
 		old_br = br;
 	}
 	ret = -E_MP3_INFO;
-	if (!afhi->chunks_total || !freq_avg || !br_avg)
+	if (!afhi->chunks_total || !freq_sum || !br_sum)
 		goto err_out;
 	afhi->chunk_table[afhi->chunks_total] = numbytes - 1;
-	afhi->bitrate = br_avg;
-	afhi->frequency = freq_avg;
+	afhi->bitrate = br_sum / afhi->chunks_total;
+	afhi->frequency = freq_sum / afhi->chunks_total;
 	afhi->channels = header_channels(&header);
 	afhi->seconds_total = (tv2ms(&total_time) + 500) / 1000;
 	tv_divide(afhi->chunks_total, &total_time, &afhi->chunk_tv);