[FFmpeg-devel] [PATCH v3 1/2] avformat: add avformat_query_seekable

[Gyan Doshi]

Utility function to report seekability features for a given input.

Useful for ffprobe and to extend seek possibilities in fftools.
---
v3:
   add some checks for seekability such as
     default stream
     demuxer seek function for NOFILE formats

 doc/APIchanges         |  3 ++
 libavformat/avformat.h | 23 +++++++++++++++
 libavformat/seek.c     | 64 ++++++++++++++++++++++++++++++++++++++++++
 libavformat/version.h  |  2 +-
 4 files changed, 91 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 65bf5a9419..879f56b572 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
 
 API changes, most recent first:
 
+2025-04-xx - xxxxxxxxxx - lavf 62.1.100 - avformat.h
+  Add avformat_query_seekable().
+
 2025-04-07 - 19e9a203b7 - lavu 60.01.100 - dict.h
   Add AV_DICT_DEDUP.
 
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 498c3020a5..295a9784fe 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -2338,6 +2338,29 @@ int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp,
  */
 int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts, int64_t ts, int64_t max_ts, int flags);
 
+#define AVSEEKABLE_IO_NORMAL       0x00000001 ///< I/O is seekable like a local file
+#define AVSEEKABLE_IO_PROTOCOL     0x00000002 ///< I/O seek is through protocol request via avio_seek_time
+#define AVSEEKABLE_VIA_DEMUXER     0x00000004 ///< demuxer has a seek function
+#define AVSEEKABLE_VIA_PKTSCAN     0x00000008 ///< seek is performed by consuming and scanning packet timestamps
+#define AVSEEKABLE_BY_TIME         0x00000100 ///< seek target can be a timestamp
+#define AVSEEKABLE_BY_BYTE         0x00000200 ///< seek target can be in bytes
+#define AVSEEKABLE_BY_FRAME        0x00000400 ///< seek target can be a frame index
+#define AVSEEKABLE_PROP_PTS        0x00010000 ///< seek target timestamp is expected to be PTS
+#define AVSEEKABLE_PROP_FAST       0x00020000 ///< demuxer allows fast but inaccurate seeking
+#define AVSEEKABLE_PROP_SLOW       0x00040000 ///< demuxer instance has no index to search within
+#define AVSEEKABLE_PROP_FWDONLY    0x00080000 ///< set seek will be equal or forward of specified seek point
+
+/**
+ * Report if and how a seek can be performed in a given input.
+ *
+ * @param s            media file handle
+ *
+ * @return 0 if no seek can be performed on input,
+ *         -1 if the fmt ctx is NULL or is not an input
+ *         else return AVSEEKABLE_ bitflags indicating seekability features.
+ */
+int avformat_query_seekable(AVFormatContext *s);
+
 /**
  * Discard all internally buffered data. This can be useful when dealing with
  * discontinuities in the byte stream. Generally works only with formats that
diff --git a/libavformat/seek.c b/libavformat/seek.c
index c0d94371e6..0a012322c0 100644
--- a/libavformat/seek.c
+++ b/libavformat/seek.c
@@ -712,6 +712,70 @@ int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts,
     return ret;
 }
 
+int avformat_query_seekable(AVFormatContext *s)
+{
+    int stream_index, ret = 0;
+
+    if (!s || !s->iformat)
+        return -1;
+
+    if (s->ctx_flags & AVFMTCTX_UNSEEKABLE)
+        return 0;
+
+    stream_index = av_find_default_stream_index(s);
+    if (stream_index < 0)
+        return 0;
+
+    if (ffifmt(s->iformat)->read_seek || ffifmt(s->iformat)->read_seek2)
+        ret |= AVSEEKABLE_VIA_DEMUXER;
+
+    if (ffifmt(s->iformat)->read_timestamp && !(s->iformat->flags & AVFMT_NOBINSEARCH))
+        ret |= AVSEEKABLE_VIA_PKTSCAN;
+
+    if (!(s->iformat->flags & AVFMT_NOTIMESTAMPS))
+        ret |= AVSEEKABLE_BY_TIME;
+
+    // TODO: incomplete, a few demuxers don't set flag but error out on byte seek
+    if (!(s->iformat->flags & AVFMT_NO_BYTE_SEEK))
+        ret |= AVSEEKABLE_BY_BYTE;
+
+    // TODO: no flag for frame seeking. Add flag and enable this check
+    if (s->iformat->flags & 0)
+        ret |= AVSEEKABLE_BY_FRAME;
+
+    if (s->iformat->flags & AVFMT_SEEK_TO_PTS)
+        ret |= AVSEEKABLE_PROP_PTS;
+
+    // TODO: flag exists but not added to the demuxers which support it
+    if (s->iformat->flags & AVFMT_FLAG_FAST_SEEK)
+        ret |= AVSEEKABLE_PROP_FAST;
+
+    if (!(ret & AVSEEKABLE_VIA_DEMUXER) && ret & AVSEEKABLE_VIA_PKTSCAN)
+        ret |= (AVSEEKABLE_PROP_FWDONLY | AVSEEKABLE_PROP_SLOW);
+
+    if (!s->pb) {
+        if ( !(s->iformat->flags & AVFMT_NOFILE) || !(ret & AVSEEKABLE_VIA_DEMUXER) )
+            return 0;
+    } else {
+        if (!s->pb->seekable)
+            return 0;
+
+        if (s->pb->seekable & AVIO_SEEKABLE_NORMAL)
+            ret |= AVSEEKABLE_IO_NORMAL;
+        if (s->pb->seekable & AVIO_SEEKABLE_TIME)
+            ret |= AVSEEKABLE_IO_PROTOCOL;
+    }
+
+    if ( !(ret & AVSEEKABLE_VIA_DEMUXER) &&
+         !(ret & AVSEEKABLE_VIA_PKTSCAN) &&
+         !(ret & AVSEEKABLE_BY_BYTE) &&
+         !(ret & AVSEEKABLE_IO_PROTOCOL) &&
+         (s->iformat->flags & AVFMT_NOGENSEARCH) )
+        ret = 0;
+
+    return ret;
+}
+
 /** Flush the frame reader. */
 void ff_read_frame_flush(AVFormatContext *s)
 {
diff --git a/libavformat/version.h b/libavformat/version.h
index 752aac16f7..a7c80dc564 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -31,7 +31,7 @@
 
 #include "version_major.h"
 
-#define LIBAVFORMAT_VERSION_MINOR   0
+#define LIBAVFORMAT_VERSION_MINOR   1
 #define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
-- 
2.49.0