From 75dce88a20846bcfef66b82aa9b8b6f031dc6eb9 Mon Sep 17 00:00:00 2001
From: Scott Lamb <slamb@slamb.org>
Date: Fri, 14 Aug 2020 21:21:59 -0700
Subject: [PATCH] use "-fflags nobuffer" on ffmpeg rtsp stream

This works around the problem in which the first frame has an incorrect
pts. Before we waited for the second key frame, which added annoying
latency to starting the stream.

I don't think the buffering does anything helpful for Moonfire NVR
anyway.
---
 src/stream.rs | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/src/stream.rs b/src/stream.rs
index fc7de36..99fa043 100644
--- a/src/stream.rs
+++ b/src/stream.rs
@@ -33,7 +33,7 @@ use cstr::*;
 use failure::{Error, bail};
 use ffmpeg;
 use lazy_static::lazy_static;
-use log::{debug, info, warn};
+use log::{debug, warn};
 use std::convert::TryFrom;
 use std::ffi::CString;
 use std::result::Result;
@@ -78,7 +78,7 @@ impl Ffmpeg {
 impl Opener<FfmpegStream> for Ffmpeg {
     fn open(&self, src: Source) -> Result<FfmpegStream, Error> {
         use ffmpeg::avformat::InputFormatContext;
-        let (mut input, discard_first) = match src {
+        let mut input = match src {
             #[cfg(test)]
             Source::File(filename) => {
                 let mut open_options = ffmpeg::avutil::Dictionary::new();
@@ -92,15 +92,20 @@ impl Opener<FfmpegStream> for Ffmpeg {
                     warn!("While opening URL {}, some options were not understood: {}",
                           url, open_options);
                 }
-                (i, false)
+                i
             }
             Source::Rtsp{url, redacted_url} => {
                 let mut open_options = ffmpeg::avutil::Dictionary::new();
                 open_options.set(cstr!("rtsp_transport"), cstr!("tcp")).unwrap();
                 open_options.set(cstr!("user-agent"), cstr!("moonfire-nvr")).unwrap();
+
                 // 10-second socket timeout, in microseconds.
                 open_options.set(cstr!("stimeout"), cstr!("10000000")).unwrap();
 
+                // Without this option, the first packet has an incorrect pts.
+                // https://trac.ffmpeg.org/ticket/5018
+                open_options.set(cstr!("fflags"), cstr!("nobuffer")).unwrap();
+
                 // Moonfire NVR currently only supports video, so receiving audio is wasteful.
                 // It also triggers <https://github.com/scottlamb/moonfire-nvr/issues/36>.
                 open_options.set(cstr!("allowed_media_types"), cstr!("video")).unwrap();
@@ -110,7 +115,7 @@ impl Opener<FfmpegStream> for Ffmpeg {
                     warn!("While opening URL {}, some options were not understood: {}",
                           redacted_url, open_options);
                 }
-                (i, true)
+                i
             },
         };
 
@@ -133,17 +138,10 @@ impl Opener<FfmpegStream> for Ffmpeg {
             None => bail!("no video stream"),
         };
 
-        let mut stream = FfmpegStream{
+        Ok(FfmpegStream {
             input,
             video_i,
-        };
-
-        if discard_first {
-            info!("Discarding the first packet to work around https://trac.ffmpeg.org/ticket/5018");
-            stream.get_next()?;
-        }
-
-        Ok(stream)
+        })
     }
 }