Fix task creation with video file when there are no valid keyframes (#…

…7838)

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit


- **Bug Fixes**
- Fixed an issue where task creation from videos without valid keyframes
could cause errors.
- **New Features**
	- Enhanced video stream handling to support videos without keyframes.
- Improved manifest management with new checks for empty states and
better index handling.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

changelog.d/20240503_110728_maria_fix_task_creation_from_video_with_no_valid_keyframes.md

@@ -0,0 +1,4 @@
+### Fixed
+
+- Task creation from a video file without keyframes allowing for random iteration
+  (<https://github.com/cvat-ai/cvat/pull/7838>)

utils/dataset_manifest/core.py

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: MIT
 
 from enum import Enum
-from io import StringIO
+from io import StringIO, BytesIO
 import av
 import json
 import os
@@ -13,12 +13,11 @@
 from contextlib import closing
 from PIL import Image
 from json.decoder import JSONDecodeError
-from io import BytesIO
 
-from .errors import InvalidManifestError, InvalidVideoFrameError
+from .errors import InvalidManifestError, InvalidVideoError
 from .utils import SortingMethod, md5_hash, rotate_image, sort
 
-from typing import Dict, List, Union, Optional
+from typing import Dict, List, Union, Optional, Iterator, Tuple
 
 class VideoStreamReader:
     def __init__(self, source_path, chunk_size, force):
@@ -33,7 +32,7 @@ def __init__(self, source_path, chunk_size, force):
                 for frame in packet.decode():
                     # check type of first frame
                     if not frame.pict_type.name == 'I':
-                        raise InvalidVideoFrameError('First frame is not key frame')
+                        raise InvalidVideoError('The first frame is not a key frame')
 
                     # get video resolution
                     if video_stream.metadata.get('rotate'):
@@ -75,40 +74,66 @@ def validate_key_frame(self, container, video_stream, key_frame):
                     return False
                 return True
 
-    def __iter__(self):
-        with closing(av.open(self.source_path, mode='r')) as container:
-            video_stream = self._get_video_stream(container)
-            frame_pts, frame_dts = -1, -1
-            index, key_frame_number = 0, 0
-            for packet in container.demux(video_stream):
+    def __iter__(self) -> Iterator[Union[int, Tuple[int, int, str]]]:
+        """
+        Iterate over video frames and yield key frames or indexes.
+
+        Yields:
+            Union[Tuple[int, int, str], int]: (frame index, frame timestamp, frame MD5) or frame index.
+        """
+        # Open containers for reading frames and checking movement on them
+        with (
+            closing(av.open(self.source_path, mode='r')) as reading_container,
+            closing(av.open(self.source_path, mode='r')) as checking_container
+        ):
+            reading_v_stream = self._get_video_stream(reading_container)
+            checking_v_stream = self._get_video_stream(checking_container)
+            prev_pts: Optional[int] = None
+            prev_dts: Optional[int] = None
+            index, key_frame_count = 0, 0
+
+            for packet in reading_container.demux(reading_v_stream):
                 for frame in packet.decode():
-                    if None not in {frame.pts, frame_pts} and frame.pts <= frame_pts:
-                        raise InvalidVideoFrameError('Invalid pts sequences')
-                    if None not in {frame.dts, frame_dts} and frame.dts <= frame_dts:
-                        raise InvalidVideoFrameError('Invalid dts sequences')
-                    frame_pts, frame_dts = frame.pts, frame.dts
+                    # Check PTS and DTS sequences for validity
+                    if None not in {frame.pts, prev_pts} and frame.pts <= prev_pts:
+                        raise InvalidVideoError('Detected non-increasing PTS sequence in the video')
+                    if None not in {frame.dts, prev_dts} and frame.dts <= prev_dts:
+                        raise InvalidVideoError('Detected non-increasing DTS sequence in the video')
+                    prev_pts, prev_dts = frame.pts, frame.dts
 
                     if frame.key_frame:
-                        key_frame_number += 1
-                        ratio = (index + 1) // key_frame_number
-
-                        if ratio >= self._upper_bound and not self._force:
-                            raise AssertionError('Too few keyframes')
-
-                        key_frame = {
-                            'index': index,
+                        key_frame_data = {
                             'pts': frame.pts,
-                            'md5': md5_hash(frame)
+                            'md5': md5_hash(frame),
                         }
 
-                        with closing(av.open(self.source_path, mode='r')) as checked_container:
-                            checked_container.seek(offset=key_frame['pts'], stream=video_stream)
-                            isValid = self.validate_key_frame(checked_container, video_stream, key_frame)
-                            if isValid:
-                                yield (index, key_frame['pts'], key_frame['md5'])
+                        # Check that it is possible to seek to this key frame using frame.pts
+                        checking_container.seek(
+                            offset=key_frame_data['pts'],
+                            stream=checking_v_stream,
+                        )
+                        is_valid_key_frame = self.validate_key_frame(
+                            checking_container,
+                            checking_v_stream,
+                            key_frame_data,
+                        )
+
+                        if is_valid_key_frame:
+                            key_frame_count += 1
+                            yield (index, key_frame_data['pts'], key_frame_data['md5'])
+                        else:
+                            yield index
                     else:
                         yield index
+
                     index += 1
+                    key_frame_ratio = index // (key_frame_count or 1)
+
+                    # Check if the number of key frames meets the upper bound
+                    if key_frame_ratio >= self._upper_bound and not self._force:
+                        raise InvalidVideoError('The number of keyframes is not enough for smooth iteration over the video')
+
+            # Update frames number if not already set
             if not self._frames_number:
                 self._frames_number = index
 
@@ -317,6 +342,9 @@ def __getitem__(self, number):
     def __len__(self):
         return len(self._index)
 
+    def is_empty(self) -> bool:
+        return not len(self)
+
 class _ManifestManager(ABC):
     BASE_INFORMATION = {
         'version' : 1,
@@ -405,10 +433,12 @@ def manifest(self):
         return self._manifest
 
     def __len__(self):
-        if hasattr(self, '_index'):
-            return len(self._index)
-        else:
-            return None
+        return len(self._index)
+
+    def is_empty(self) -> bool:
+        if self._index.is_empty():
+            self._index.load()
+        return self._index.is_empty()
 
     def __getitem__(self, item):
         if isinstance(item, slice):
@@ -482,6 +512,9 @@ def create(self, *, _tqdm=None): # pylint: disable=arguments-differ
 
         self.set_index()
 
+        if self.is_empty() and not self._reader._force:
+            raise InvalidManifestError('Empty manifest file has been created')
+
     def partial_update(self, number, properties):
         pass
 

utils/dataset_manifest/errors.py

@@ -7,7 +7,7 @@ class BasicError(Exception):
     The basic exception type for all exceptions in the library
     """
 
-class InvalidVideoFrameError(BasicError):
+class InvalidVideoError(BasicError):
     """
     Indicates an invalid video frame
     """