Stowage/ffmpeg
2
0
Fork 0
mirror of https://git.ffmpeg.org/ffmpeg.git synced 2025-12-08 06:09:50 +00:00
Code Issues Projects Releases Packages Wiki Activity

avformat/dhav: fix backward scanning for get_duration and optimize seeking

Browse source 
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 to avoid additional seek operations.

Co-authored-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Justin Ruggles <justinr@vimeo.com>
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
This commit is contained in:
Justin Ruggles 2025-03-21 14:00:38 -04:00 • committed by Derek Buitenhuis
parent c8b09fb0ac
commit 36ec9217e6
1 changed files with 39 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

54
libavformat/dhav.c
View file

@ -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);