[FFmpeg-devel] [PATCH] dpx.c: Better support for reading fps from headers

[Bob Maple]

Relatively simple patch to better support fetching the fps from DPX files.

DPX has 2 separate "industry" headers -- both which are required, but
not to actually be legitimately filled with anything.  Currently ffmpeg
only looks in the Film header to get the FPS, but many industry apps
write into the TV header since it's more applicable.  Some write to
both...  I've found the DPX landscape to be the wild wild west, all
sorts of abuse of the standard (which its self is vague in several places.)

In any case, this looks in the Film header first then tries the TV
header.  Nothing too crazy.  I'd like to add timecode support next but
this is my first real foray into the ffmpeg source and I'm still totally
lost as to the flow of things.

(helps if I actually attach this time..)
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>From b5db33ff18db6b0bae07968bd3f6dcf986956804 Mon Sep 17 00:00:00 2001
From: Bob Maple <bobm-ffdev at burner.com>
Date: Thu, 3 Jul 2014 17:30:53 -0600
Subject: [PATCH] dpx.c: Better support for reading fps from headers

---
 libavcodec/dpx.c |   21 ++++++++++++++-------
 1 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/libavcodec/dpx.c b/libavcodec/dpx.c
index 5f05cd8..acda974 100644
--- a/libavcodec/dpx.c
+++ b/libavcodec/dpx.c
@@ -147,14 +147,21 @@ static int decode_frame(AVCodecContext *avctx,
     else
         avctx->sample_aspect_ratio = (AVRational){ 0, 1 };
 
-    if (offset >= 1724 + 4) {
-        buf = avpkt->data + 1724;
+    // Look in the 'Film Industry' header and the 'TV Industry' header for fps
+    buf = avpkt->data + 1724;
+    i = read32(&buf, endian);
+
+    // All undefined fields are supposed to be set to all 0xFF
+    // but some writers use +inf here
+    if (i == 0x7F800000 || i == 0xFFFFFFFF) {
+        buf = avpkt->data + 1940;
         i = read32(&buf, endian);
-        if(i) {
-            AVRational q = av_d2q(av_int2float(i), 4096);
-            if (q.num > 0 && q.den > 0)
-                avctx->time_base = av_inv_q(q);
-        }
+    }
+
+    if(i) {
+        AVRational q = av_d2q(av_int2float(i), 4096);
+        if (q.num > 0 && q.den > 0)
+            avctx->time_base = av_inv_q(q);
     }
 
     switch (descriptor) {
-- 
1.7.1