[Async Attachment Upload] Initial implementation

Signed-off-by: Sahil Kumar <[email protected]>

packages/stream_chat_flutter/lib/src/video_service.dart

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+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:synchronized/synchronized.dart';
+import 'package:video_compress/video_compress.dart';
+import 'package:video_thumbnail/video_thumbnail.dart';
+import 'package:meta/meta.dart';
+
+class IVideoService {
+  static final IVideoService instance = IVideoService._();
+  final _lock = Lock();
+
+  IVideoService._();
+
+  /// compress video from [path]
+  /// compress video from [path] return [Future<MediaInfo>]
+  ///
+  /// you can choose its quality by [quality],
+  /// determine whether to delete his source file by [deleteOrigin]
+  /// optional parameters [startTime] [duration] [includeAudio] [frameRate]
+  ///
+  /// ## example
+  /// ```dart
+  /// final info = await _flutterVideoCompress.compressVideo(
+  ///   file.path,
+  ///   deleteOrigin: true,
+  /// );
+  /// debugPrint(info.toJson());
+  /// ```
+  Future<MediaInfo> compressVideo(String path) async {
+    return _lock.synchronized(() {
+      return VideoCompress.compressVideo(
+        path,
+      );
+    });
+  }
+
+  /// Generates a thumbnail image data in memory as UInt8List, it can be easily used by Image.memory(...).
+  /// The video can be a local video file, or an URL repreents iOS or Android native supported video format.
+  /// Speicify the maximum height or width for the thumbnail or 0 for same resolution as the original video.
+  /// The lower quality value creates lower quality of the thumbnail image, but it gets ignored for PNG format.
+  Future<Uint8List> generateVideoThumbnail({
+    @required String video,
+    ImageFormat imageFormat = ImageFormat.PNG,
+    int maxHeight = 0,
+    int maxWidth = 0,
+    int timeMs = 0,
+    int quality = 10,
+  }) {
+    return VideoThumbnail.thumbnailData(
+      video: video,
+      imageFormat: imageFormat,
+      maxHeight: maxHeight,
+      maxWidth: maxWidth,
+      timeMs: timeMs,
+      quality: quality,
+    );
+  }
+}
+
+// ignore: non_constant_identifier_names
+IVideoService get VideoService => IVideoService.instance;