Add a function to the reader to read in fragments from a different reader

src/reader.rs

@@ -129,6 +129,92 @@ impl<R: Read + Seek> Mp4Reader<R> {
         })
     }
 
+    pub fn read_fragment_header<FR: Read + Seek>(
+        &self,
+        mut reader: FR,
+        size: u64,
+    ) -> Result<Mp4Reader<FR>> {
+        let start = reader.stream_position()?;
+
+        let mut moofs = Vec::new();
+        let mut moof_offsets = Vec::new();
+
+        let mut current = start;
+        while current < size {
+            // Get box header.
+            let header = BoxHeader::read(&mut reader)?;
+            let BoxHeader { name, size: s } = header;
+            if s > size {
+                return Err(Error::InvalidData(
+                    "file contains a box with a larger size than it",
+                ));
+            }
+
+            // Break if size zero BoxHeader, which can result in dead-loop.
+            if s == 0 {
+                break;
+            }
+
+            // Match and parse the atom boxes.
+            match name {
+                BoxType::MdatBox => {
+                    skip_box(&mut reader, s)?;
+                }
+                BoxType::MoofBox => {
+                    let moof_offset = reader.stream_position()? - 8;
+                    let moof = MoofBox::read_box(&mut reader, s)?;
+                    moofs.push(moof);
+                    moof_offsets.push(moof_offset);
+                }
+                _ => {
+                    // XXX warn!()
+                    skip_box(&mut reader, s)?;
+                }
+            }
+            current = reader.stream_position()?;
+        }
+
+        if moofs.is_empty() {
+            return Err(Error::BoxNotFound(BoxType::MoofBox));
+        }
+
+        let size = current - start;
+        let mut tracks: HashMap<u32, Mp4Track> = self
+            .moov
+            .traks
+            .iter()
+            .map(|trak| (trak.tkhd.track_id, Mp4Track::from(trak)))
+            .collect();
+
+        let mut default_sample_duration = 0;
+        if let Some(ref mvex) = &self.moov.mvex {
+            default_sample_duration = mvex.trex.default_sample_duration
+        }
+
+        for (moof, moof_offset) in moofs.iter().zip(moof_offsets) {
+            for traf in moof.trafs.iter() {
+                let track_id = traf.tfhd.track_id;
+                if let Some(track) = tracks.get_mut(&track_id) {
+                    track.default_sample_duration = default_sample_duration;
+                    track.moof_offsets.push(moof_offset);
+                    track.trafs.push(traf.clone())
+                } else {
+                    return Err(Error::TrakNotFound(track_id));
+                }
+            }
+        }
+
+        Ok(Mp4Reader {
+            reader,
+            ftyp: self.ftyp.clone(),
+            moov: self.moov.clone(),
+            moofs,
+            emsgs: Vec::new(),
+            tracks,
+            size,
+        })
+    }
+
     pub fn size(&self) -> u64 {
         self.size
     }

tests/lib.rs

@@ -176,3 +176,36 @@ fn test_read_metadata() {
     assert_eq!(poster.len(), want_poster.len());
     assert_eq!(poster, want_poster.as_slice());
 }
+
+#[test]
+fn test_read_fragments() {
+    let mp4 = get_reader("tests/samples/minimal_init.mp4");
+
+    assert_eq!(692, mp4.size());
+    assert_eq!(5, mp4.compatible_brands().len());
+
+    let sample_count = mp4.sample_count(1).unwrap();
+    assert_eq!(sample_count, 0);
+
+    let f = File::open("tests/samples/minimal_fragment.m4s").unwrap();
+    let f_size = f.metadata().unwrap().len();
+    let frag_reader = BufReader::new(f);
+
+    let mut mp4_fragment = mp4.read_fragment_header(frag_reader, f_size).unwrap();
+    let sample_count = mp4_fragment.sample_count(1).unwrap();
+    assert_eq!(sample_count, 1);
+    let sample_1_1 = mp4_fragment.read_sample(1, 1).unwrap().unwrap();
+    assert_eq!(sample_1_1.bytes.len(), 751);
+    assert_eq!(
+        sample_1_1,
+        mp4::Mp4Sample {
+            start_time: 0,
+            duration: 512,
+            rendering_offset: 0,
+            is_sync: true,
+            bytes: mp4::Bytes::from(vec![0x0u8; 751]),
+        }
+    );
+    let eos = mp4_fragment.read_sample(1, 2);
+    assert!(eos.is_err());
+}