Hi
On Wed, May 21, 2025 at 02:23:00PM +0100, Derek Buitenhuis wrote:
> 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)
> {
> 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;
>
> + if (start_pos + 16 > avio_size(s->pb))
> + return 0;
>
> + 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;calling avio_size() multiple times and assuming its always teh same value feels risky to me thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB The worst form of inequality is to try to make unequal things equal. -- Aristotle
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