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new 7ee873656c avformat/libcurl: implement -short_seek_size
7ee873656c is described below
commit 7ee873656cb5fc489c6d2966e45d448ca30aedda
Author: Niklas Haas <[email protected]>
AuthorDate: Wed Jun 24 19:21:41 2026 +0200
Commit: Niklas Haas <[email protected]>
CommitDate: Fri Sep 4 17:37:20 2026 +0000
avformat/libcurl: implement -short_seek_size
Since libcurl.c doesn't have to care about the exact number of bytes read,
we just perform the seek but defer the actual `start_request()` call until
the next on_done() callback, while simply discarding all data read in the
meantime.
Sponsored-by: nxtedition AB
Signed-off-by: Niklas Haas <[email protected]>
---
doc/protocols.texi | 9 +++++++++
libavformat/libcurl.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++----
2 files changed, 57 insertions(+), 4 deletions(-)
diff --git a/doc/protocols.texi b/doc/protocols.texi
index 9790317d28..4a82dae2ee 100644
--- a/doc/protocols.texi
+++ b/doc/protocols.texi
@@ -1166,9 +1166,18 @@ read request larger than this size (without a seek in
between), after which
the implementation will continue using requests as usual. Disabled (set to 0)
by default.
+Note that if enabling this option, it's strongly recommended to also set
+@option{short_seek_size} to the same value or higher, otherwise the HTTP
+connection may be closed and recreated for each subsequent initial request.
+
@item max_retries
Maximum number of retries after a recoverable error on a seekable transfer.
Default is @code{5}.
+
+@item short_seek_size
+Set the threshold, in bytes, for when a readahead should be preferred over a
seek and
+new HTTP request. This is useful, for example, to make sure the same connection
+is used for reading large video packets with small audio packets in between.
@end table
For more information see: @url{https://curl.se/libcurl/}.
diff --git a/libavformat/libcurl.c b/libavformat/libcurl.c
index a2f7e6201e..2196e7913f 100644
--- a/libavformat/libcurl.c
+++ b/libavformat/libcurl.c
@@ -120,6 +120,7 @@ struct CurlContext {
int64_t buffer_size;
int64_t request_size;
int64_t initial_request_size;
+ int64_t short_seek_size;
int max_retries;
int64_t logical_pos; /* next byte url_read() will return, caller
side */
@@ -131,6 +132,7 @@ struct CurlContext {
int64_t request_end; /* expected end of request, or -1 if
unknown */
int retry_count; /* consecutive recoverable failures */
int is_initial; /* using reduced request size */
+ int seek_queued; /* soft seeking; drain remaining bytes
until done */
/* Per-response-block header scratch, loop thread only. */
int hdr_accept_ranges;
@@ -211,6 +213,11 @@ static size_t write_callback(char *ptr, size_t size,
size_t nmemb, void *userdat
return CURL_WRITEFUNC_ERROR;
}
+ if (c->seek_queued) {
+ pthread_mutex_unlock(&c->mutex);
+ return bytes; /* discard */
+ }
+
space = av_fifo_can_write(c->fifo);
if (space < bytes) {
/* pause the transfer and wait for the consumer to drain. */
@@ -487,6 +494,13 @@ static void on_done(CurlContext *c, CURLcode code)
if (aborted)
return;
+ if (c->seek_queued) {
+ /* previous soft seek drain finished; can start new request now */
+ c->seek_queued = 0;
+ start_request(c);
+ return;
+ }
+
if (code == CURLE_OK && c->stream_ok) {
c->retry_count = 0;
int64_t file_end = c->content_size > 0 ? c->content_size - 1 : -1;
@@ -531,6 +545,19 @@ static void on_done(CurlContext *c, CURLcode code)
/* event loop thread + command queue */
/* ------------------------------------------------------------------------- */
+static int test_short_seek(CurlContext *c)
+{
+ if (c->seek_queued)
+ return 1; /* short seek already queued */
+
+ if (c->short_seek_size <= 0 || /* short seek disabled */
+ c->request_end < 0) /* content size not known */
+ return 0;
+
+ const int64_t last = c->request_end - c->request_start;
+ return last - c->request_received < c->short_seek_size;
+}
+
static void execute_command(CurlLoop *loop, CurlCmd *cmd)
{
CurlContext *c = cmd->ctx;
@@ -553,18 +580,25 @@ static void execute_command(CurlLoop *loop, CurlCmd *cmd)
curl_easy_pause(c->easy, CURLPAUSE_CONT);
break;
case CMD_SEEK:
- if (c->active) {
+ if (c->active && test_short_seek(c)) {
+ c->seek_queued = 1;
+ } else if (c->active) {
curl_multi_remove_handle(loop->multi, c->easy);
c->active = 0;
}
pthread_mutex_lock(&c->mutex);
av_fifo_reset2(c->fifo);
+ const int was_paused = c->paused;
c->paused = 0;
c->status = 0;
pthread_mutex_unlock(&c->mutex);
- c->request_start = cmd->pos;
- c->retry_count = 0;
- start_request(c);
+ c->request_start = cmd->pos;
+ c->request_received = 0;
+ c->retry_count = 0;
+ if (!c->seek_queued)
+ start_request(c);
+ else if (was_paused)
+ curl_easy_pause(c->easy, CURLPAUSE_CONT);
break;
}
}
@@ -1174,6 +1208,14 @@ static int libcurl_close(URLContext *h)
return 0;
}
+static int libcurl_get_short_seek(URLContext *h)
+{
+ CurlContext *c = h->priv_data;
+ if (c->short_seek_size >= 1)
+ return FFMIN(c->short_seek_size, INT_MAX);
+ return AVERROR(ENOSYS);
+}
+
#define OFFSET(x) offsetof(CurlContext, x)
#define D AV_OPT_FLAG_DECODING_PARAM
#define E AV_OPT_FLAG_ENCODING_PARAM
@@ -1207,6 +1249,7 @@ static const AVOption options[] = {
{ "2-prior-knowledge", "HTTP/2 without an upgrade handshake", 0,
AV_OPT_TYPE_CONST, { .i64 = CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE }, 0, 0, D,
.unit = "http_version" },
{ "3", "HTTP/3, fall back to earlier versions", 0,
AV_OPT_TYPE_CONST, { .i64 = CURL_HTTP_VERSION_3 }, 0, 0, D,
.unit = "http_version" },
{ "3only", "HTTP/3 only", 0,
AV_OPT_TYPE_CONST, { .i64 = CURL_HTTP_VERSION_3ONLY }, 0, 0, D,
.unit = "http_version" },
+ { "short_seek_size", "threshold to favor readahead over seek",
OFFSET(short_seek_size), AV_OPT_TYPE_INT64, { .i64 = 0 }, 0, INT64_MAX, D },
{ NULL }
};
@@ -1223,6 +1266,7 @@ const URLProtocol ff_libcurl_protocol = {
.url_read = libcurl_read,
.url_seek = libcurl_seek,
.url_close = libcurl_close,
+ .url_get_short_seek = libcurl_get_short_seek,
.priv_data_size = sizeof(CurlContext),
.priv_data_class = &libcurl_context_class,
.flags = URL_PROTOCOL_FLAG_NETWORK,
--
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