Restore read_moov behavior allowing multiple moov boxes

The behavior change was introduced by c196ca8

Despite being invalid according to ISOBMFF (ISO 14496-12:2015) § 8.2.1.1, this
restores the original behavior, while maintaining the interface that eliminates
the necessity for callers to create a `MediaContext` object to pass in.

Author: baumanj

mp4parse/src/lib.rs

@@ -738,12 +738,6 @@ pub struct MediaContext {
     pub userdata: Option<Result<UserdataBox>>,
 }
 
-impl MediaContext {
-    pub fn new() -> MediaContext {
-        Default::default()
-    }
-}
-
 /// An ISOBMFF item as described by an iloc box. For the sake of avoiding copies,
 /// this can either be represented by the `Location` variant, which indicates
 /// where the data exists within a `MediaDataBox` stored separately, or the
@@ -2278,7 +2272,7 @@ pub fn read_mp4<T: Read>(f: &mut T) -> Result<MediaContext> {
                 debug!("{:?}", ftyp);
             }
             BoxType::MovieBox => {
-                context = Some(read_moov(&mut b)?);
+                context = Some(read_moov(&mut b, context)?);
             }
             _ => skip_box_content(&mut b)?,
         };
@@ -2301,6 +2295,8 @@ pub fn read_mp4<T: Read>(f: &mut T) -> Result<MediaContext> {
     context.ok_or(Error::NoMoov)
 }
 
+/// Parse a Movie Header Box
+/// See ISOBMFF (ISO 14496-12:2015) § 8.2.2
 fn parse_mvhd<T: Read>(f: &mut BMFFBox<T>) -> Result<Option<MediaTimeScale>> {
     let mvhd = read_mvhd(f)?;
     debug!("{:?}", mvhd);
@@ -2311,14 +2307,19 @@ fn parse_mvhd<T: Read>(f: &mut BMFFBox<T>) -> Result<Option<MediaTimeScale>> {
     Ok(timescale)
 }
 
-fn read_moov<T: Read>(f: &mut BMFFBox<T>) -> Result<MediaContext> {
+/// Parse a Movie Box
+/// See ISOBMFF (ISO 14496-12:2015) § 8.2.1
+/// Note that despite the spec indicating "exactly one" moov box should exist at
+/// the file container level, we support reading and merging multiple moov boxes
+/// such as with tests/test_case_1185230.mp4.
+fn read_moov<T: Read>(f: &mut BMFFBox<T>, context: Option<MediaContext>) -> Result<MediaContext> {
     let MediaContext {
         mut timescale,
         mut tracks,
         mut mvex,
         mut psshs,
         mut userdata,
-    } = Default::default();
+    } = context.unwrap_or_default();
 
     let mut iter = f.box_iter();
     while let Some(mut b) = iter.next_box()? {
@@ -2396,6 +2397,8 @@ fn read_pssh<T: Read>(src: &mut BMFFBox<T>) -> Result<ProtectionSystemSpecificHe
     })
 }
 
+/// Parse a Movie Extends Box
+/// See ISOBMFF (ISO 14496-12:2015) § 8.8.1
 fn read_mvex<T: Read>(src: &mut BMFFBox<T>) -> Result<MovieExtendsBox> {
     let mut iter = src.box_iter();
     let mut fragment_duration = None;
@@ -2421,6 +2424,8 @@ fn read_mehd<T: Read>(src: &mut BMFFBox<T>) -> Result<MediaScaledTime> {
     Ok(MediaScaledTime(fragment_duration))
 }
 
+/// Parse a Track Box
+/// See ISOBMFF (ISO 14496-12:2015) § 8.3.1.
 fn read_trak<T: Read>(f: &mut BMFFBox<T>, track: &mut Track) -> Result<()> {
     let mut iter = f.box_iter();
     while let Some(mut b) = iter.next_box()? {
@@ -3940,6 +3945,7 @@ fn read_schm<T: Read>(src: &mut BMFFBox<T>) -> Result<SchemeTypeBox> {
 }
 
 /// Parse a metadata box inside a moov, trak, or mdia box.
+/// See ISOBMFF (ISO 14496-12:2015) § 8.10.1.
 fn read_udta<T: Read>(src: &mut BMFFBox<T>) -> Result<UserdataBox> {
     let mut iter = src.box_iter();
     let mut udta = UserdataBox { meta: None };

mp4parse/src/tests.rs

@@ -1248,7 +1248,7 @@ fn read_invalid_pssh() {
     let mut iter = super::BoxIter::new(&mut stream);
     let mut stream = iter.next_box().unwrap().unwrap();
 
-    match super::read_moov(&mut stream) {
+    match super::read_moov(&mut stream, None) {
         Err(Error::InvalidData(s)) => assert_eq!(s, "read_buf size exceeds BUF_SIZE_LIMIT"),
         _ => panic!("unexpected result with invalid descriptor"),
     }

mp4parse/tests/public.rs

@@ -618,6 +618,24 @@ fn public_video_av1() {
     }
 }
 
+#[test]
+fn public_mp4_bug_1185230() {
+    let input = &mut File::open("tests/test_case_1185230.mp4").expect("Unknown file");
+    let context = mp4::read_mp4(input).expect("read_mp4 failed");
+    let number_video_tracks = context
+        .tracks
+        .iter()
+        .filter(|t| t.track_type == mp4::TrackType::Video)
+        .count();
+    let number_audio_tracks = context
+        .tracks
+        .iter()
+        .filter(|t| t.track_type == mp4::TrackType::Audio)
+        .count();
+    assert_eq!(number_video_tracks, 2);
+    assert_eq!(number_audio_tracks, 2);
+}
+
 #[test]
 fn public_avif_primary_item() {
     let input = &mut File::open(IMAGE_AVIF).expect("Unknown file");