From: Justin Ruggles <just...@vimeo.com>
The backwards scanning done for incomplete final packets should not
assume a specific alignment at the end of the file. Truncated files
result in hundreds of thousands of seeks if the final packet does not
fall on a specific byte boundary, which can be extremely slow.
For example, with HTTP, each backwards seek results in a separate
HTTP request.
This changes the scanning to check for the end tag 1 byte at a time
and buffers the last 1 MiB using ffio_ensure_seekback to avoid additional
seek operations.
Co-authored-by: Derek Buitenhuis <derek.buitenh...@gmail.com>
Signed-off-by: Justin Ruggles <just...@vimeo.com>
Signed-off-by: Derek Buitenhuis <derek.buitenh...@gmail.com>
---
libavformat/dhav.c | 54 +++++++++++++++++++++++++++++++++-------------
1 file changed, 39 insertions(+), 15 deletions(-)
diff --git a/libavformat/dhav.c b/libavformat/dhav.c
index b2ead99609..d9db775802 100644
--- a/libavformat/dhav.c
+++ b/libavformat/dhav.c
@@ -22,6 +22,7 @@
#include <time.h>
+#include "libavutil/intreadwrite.h"
#include "libavutil/mem.h"
#include "libavutil/parseutils.h"
#include "avio_internal.h"
@@ -232,37 +233,60 @@ static void get_timeinfo(unsigned date, struct tm
*timeinfo)
timeinfo->tm_sec = sec;
}
+#define MAX_DURATION_BUFFER_SIZE (1024*1024)
+
static int64_t get_duration(AVFormatContext *s)
{
- DHAVContext *dhav = s->priv_data;
int64_t start_pos = avio_tell(s->pb);
+ int64_t end_pos = -1;
int64_t start = 0, end = 0;
struct tm timeinfo;
- int max_interations = 100000;
+ uint8_t *end_buffer;
+ int64_t end_buffer_size;
+ int64_t end_buffer_pos;
+ int64_t offset;
+ unsigned date;
if (!s->pb->seekable)
return 0;
- avio_seek(s->pb, avio_size(s->pb) - 8, SEEK_SET);
- while (avio_tell(s->pb) > 12 && max_interations--) {
- if (avio_rl32(s->pb) == MKTAG('d','h','a','v')) {
- int64_t seek_back = avio_rl32(s->pb);
+ if (start_pos + 16 > avio_size(s->pb))
+ return 0;
- avio_seek(s->pb, -seek_back, SEEK_CUR);
- read_chunk(s);
- get_timeinfo(dhav->date, &timeinfo);
- end = av_timegm(&timeinfo) * 1000LL;
+ avio_skip(s->pb, 16);
+ date = avio_rl32(s->pb);
+ get_timeinfo(date, &timeinfo);
+ start = av_timegm(&timeinfo) * 1000LL;
+
+ end_buffer_size = FFMIN(MAX_DURATION_BUFFER_SIZE, avio_size(s->pb));
+ end_buffer = av_malloc(end_buffer_size);
+ if (!end_buffer) {
+ avio_seek(s->pb, start_pos, SEEK_SET);
+ return 0;
+ }
+ end_buffer_pos = avio_size(s->pb) - end_buffer_size;
+ avio_seek(s->pb, end_buffer_pos, SEEK_SET);
+ avio_read(s->pb, end_buffer, end_buffer_size);
+
+ offset = end_buffer_size - 8;
+ while (offset > 0) {
+ if (AV_RL32(end_buffer + offset) == MKTAG('d','h','a','v')) {
+ int64_t seek_back = AV_RL32(end_buffer + offset + 4);
+ end_pos = end_buffer_pos + offset - seek_back + 8;
break;
} else {
- avio_seek(s->pb, -12, SEEK_CUR);
+ offset -= 9;
}
}
- avio_seek(s->pb, start_pos, SEEK_SET);
+ if (end_pos < 0 || end_pos + 16 > end_buffer_pos + end_buffer_size) {
+ avio_seek(s->pb, start_pos, SEEK_SET);
+ return 0;
+ }
- read_chunk(s);
- get_timeinfo(dhav->date, &timeinfo);
- start = av_timegm(&timeinfo) * 1000LL;
+ date = AV_RL32(end_buffer + (end_pos - end_buffer_pos) + 16);
+ get_timeinfo(date, &timeinfo);
+ end = av_timegm(&timeinfo) * 1000LL;
avio_seek(s->pb, start_pos, SEEK_SET);
--
2.49.0
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