[PR] mxfdec: Populate frame rate info for streams (PR #23929)

PR #23929 opened by anders-mjoll
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23929
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23929.patch

# Summary of changes

Briefly describe what this PR does and why.

MXF files containing PAFF encoded interlaced h264 will be misreported by ffprobe to have half the frame rate it actually has. This is because for most container formats PAFF interlaced h264 produces one AVPacket per field. Two AVPackets pushed into the h264 decoder will produce one AVFrame. In order to compensate for this common behavior the general probing code will divide the packet rate by two in order to calculate the frame rate. For MXF files this is not the behavior as both fields are returned as a single AVPacket. So for MXF the packet rate is equal to the frame rate and the PAFF compensation code results in half the frame rate being reported. Instead of fixing the MXF demuxer so that it returns one AVPacket for each field OR fixing the probing code so that it accounts for one AVPac
 ket having two fields I just modified the MXF demuxer so that it provides the frame rate explicitly. For MXF files this information is always known anyway.


>From f6b4a29d96d4b74697da746915b07e84e749a6e2 Mon Sep 17 00:00:00 2001
From: Anders Rein <[email protected]>
Date: Mon, 27 Jul 2026 20:11:31 +0200
Subject: [PATCH] mxfdec: Populate frame rate info for streams

---
 libavformat/mxfdec.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
index 4ba4af1fa7..19731a5c2a 100644
--- a/libavformat/mxfdec.c
+++ b/libavformat/mxfdec.c
@@ -2995,6 +2995,16 @@ static int mxf_parse_structural_metadata(MXFContext *mxf)
                 }
             }
 
+            /* Frame wrapped H.264 stores exactly one coded frame per edit unit,
+             * so the edit rate is the frame rate. Without this, PAFF streams get
+             * a halved avg_frame_rate: the packet holds two field pictures, but
+             * the parser only reports the first one and thus a single field. */
+            if (st->codecpar->codec_id == AV_CODEC_ID_H264 &&
+                source_track->wrapping == FrameWrapped) {
+                st->avg_frame_rate = source_track->edit_rate;
+                st->r_frame_rate = st->avg_frame_rate;
+            }
+
             if (st->codecpar->codec_id == AV_CODEC_ID_PRORES) {
                 switch (descriptor->essence_codec_ul[14]) {
                 case 1: st->codecpar->codec_tag = MKTAG('a','p','c','o'); break;
-- 
2.52.0

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