h264_metadata bitstream fixed_frame_rate_flag fix

keshavdv · Vltnrch · commit c7deab7cab63 · 2025-04-23T17:45:56.000+02:00
After changes like ef13faf, the h264_metadata bitstream filter stopped working when using the fixed_frame_rate_flag option on an input stream that doesn't contain VUI because the default inferred value of low_hrd_delay_flag seems to be 1. ffmpeg used to raise a warning, but proceeded anyway but now aborts after the other fixes since the output is rightfully invalid. I believe this change makes the bitstream filter conform to page 403 of the ITU spec: "When fixed_frame_rate_flag is equal to 1, low_delay_hrd_flag shall be equal to 0. When low_delay_hrd_flag is not present, its value shall be inferred to be equal to 1 − fixed_frame_rate_flag."
diff --git a/Changelog b/Changelog
@@ -4,6 +4,7 @@ releases are sorted from youngest to oldest.
 version 7.1.1-mtv:
 - Molotov patches
 - Redis protocol via libhiredis
+- h264_metadata bitstream fixed_frame_rate_flag fix
 
 version 7.1.1:
  avformat/hls: Partially revert "reduce default max reload to 3"
diff --git a/libavcodec/bsf/h264_metadata.c b/libavcodec/bsf/h264_metadata.c
@@ -224,7 +224,13 @@ static int h264_metadata_update_sps(AVBSFContext *bsf,
         sps->vui.timing_info_present_flag = 1;
         need_vui = 1;
     }
-    SET_VUI_FIELD(fixed_frame_rate_flag);
+
+    // Set fixed frame rate flag and update low_delay_hrd_flag to match
+    if (ctx->fixed_frame_rate_flag >= 0) {
+        sps->vui.fixed_frame_rate_flag = ctx->fixed_frame_rate_flag;
+        sps->vui.low_delay_hrd_flag = 1 - sps->vui.fixed_frame_rate_flag;
+    }
+
     if (ctx->zero_new_constraint_set_flags) {
         sps->constraint_set4_flag = 0;
         sps->constraint_set5_flag = 0;
