Media thumbnail retriever by anilbeesetti · Pull Request #168 · anilbeesetti/nextlib

anilbeesetti · 2026-02-19T16:09:06Z

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Pull request overview

This PR adds a new MediaThumbnailRetriever class that provides a lightweight API for extracting video thumbnails and embedded artwork from media files. The implementation uses FFmpeg's libraries through JNI to decode frames at specific timestamps or frame indices, with automatic rotation handling based on video metadata.

Changes:

Added MediaThumbnailRetriever Kotlin class providing frame extraction APIs similar to Android's MediaMetadataRetriever but focused on thumbnails
Implemented C++ JNI layer using FFmpeg libraries for video decoding and frame extraction
Added ProGuard rules to preserve native methods from obfuscation
Updated CMakeLists.txt to include the new C++ source file
Updated .gitignore to exclude ffmpeg build artifacts

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
MediaThumbnailRetriever.kt	New Kotlin class providing thumbnail retrieval API with multiple data source setters (path, file descriptor, URI), frame extraction at time/index, and embedded picture retrieval
media_thumbnail_retriever.cpp	C++ JNI implementation handling FFmpeg context management, video stream selection, frame decoding, rotation detection, and bitmap conversion
CMakeLists.txt	Added media_thumbnail_retriever.cpp to the build configuration
consumer-rules.pro	New ProGuard rules file to prevent native method obfuscation
.gitignore	Added ffmpeg/cmake and ffmpeg/licenses directories to ignore list

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Copilot · 2026-02-19T16:18:37Z

mediainfo/src/main/cpp/media_thumbnail_retriever.cpp

+
+    AVStream *videoStream = context->formatContext->streams[context->videoStreamIndex];
+    int64_t targetTimestamp = av_rescale_q(timeUs, AV_TIME_BASE_Q, videoStream->time_base);
+    av_seek_frame(context->formatContext, context->videoStreamIndex, targetTimestamp, AVSEEK_FLAG_BACKWARD);


Similar to decode_frame_at_index, the return value of av_seek_frame is not checked. Consider adding error handling for seek failures.

Suggested change

av_seek_frame(context->formatContext, context->videoStreamIndex, targetTimestamp, AVSEEK_FLAG_BACKWARD);

int seekResult = av_seek_frame(context->formatContext, context->videoStreamIndex, targetTimestamp, AVSEEK_FLAG_BACKWARD);

if (seekResult < 0) {

// Failed to seek to the requested timestamp; clean up and return null.

avcodec_free_context(&codecContext);

return nullptr;

}

Copilot · 2026-02-19T16:18:37Z

mediainfo/consumer-rules.pro

+-keepclasseswithmembernames class * {
+    native <methods>;
+}


The ProGuard rule is correct, but missing an explanatory comment. In media3ext/consumer-rules.pro, the same rule includes a comment: "This prevents the names of native methods from being obfuscated." Consider adding a similar comment here for consistency and clarity.

Copilot · 2026-02-19T16:18:37Z

mediainfo/src/main/cpp/media_thumbnail_retriever.cpp

+    }
+
+    for (unsigned int i = 0; i < context->formatContext->nb_streams; ++i) {
+        AVStream *stream = context->formatContext->streams[i];


Missing null check for AVStream. Similar to the issue in create_context_from_source, the stream at index i is accessed without verification. Add a null check before accessing stream->disposition.

Suggested change

AVStream *stream = context->formatContext->streams[i];

AVStream *stream = context->formatContext->streams[i];

if (!stream) {

continue;

}

Copilot · 2026-02-19T16:18:38Z

mediainfo/src/main/java/io/github/anilbeesetti/nextlib/mediainfo/MediaThumbnailRetriever.kt

+    @Keep
+    private external fun nativeCreateFromPath(filePath: String): Long
+
+    @Keep
+    private external fun nativeCreateFromFD(fileDescriptor: Int): Long
+
+    @Keep
+    private external fun nativeGetEmbeddedPicture(handle: Long): ByteArray?
+
+    @Keep
+    private external fun nativeGetFrameAtTime(handle: Long, timeUs: Long): Bitmap?
+
+    @Keep
+    private external fun nativeGetFrameAtIndex(handle: Long, frameIndex: Int): Bitmap?
+
+    @Keep
+    private external fun nativeGetRotationDegrees(handle: Long): Int
+
+    @Keep
+    private external fun nativeRelease(handle: Long)
+
+    companion object {
+        init {
+            System.loadLibrary("mediainfo")
+        }


Native method declarations are inconsistent with the codebase convention. In FrameLoader.kt, native methods are declared in a companion object with @JvmStatic annotation. This class declares them as instance methods. For consistency and potential performance benefits (static methods have slightly lower overhead in JNI), consider moving these to a companion object with @JvmStatic.

Suggested change

@Keep

private external fun nativeCreateFromPath(filePath: String): Long

@Keep

private external fun nativeCreateFromFD(fileDescriptor: Int): Long

@Keep

private external fun nativeGetEmbeddedPicture(handle: Long): ByteArray?

@Keep

private external fun nativeGetFrameAtTime(handle: Long, timeUs: Long): Bitmap?

@Keep

private external fun nativeGetFrameAtIndex(handle: Long, frameIndex: Int): Bitmap?

@Keep

private external fun nativeGetRotationDegrees(handle: Long): Int

@Keep

private external fun nativeRelease(handle: Long)

companion object {

init {

System.loadLibrary("mediainfo")

}

companion object {

init {

System.loadLibrary("mediainfo")

}

@Keep

@JvmStatic

private external fun nativeCreateFromPath(filePath: String): Long

@Keep

@JvmStatic

private external fun nativeCreateFromFD(fileDescriptor: Int): Long

@Keep

@JvmStatic

private external fun nativeGetEmbeddedPicture(handle: Long): ByteArray?

@Keep

@JvmStatic

private external fun nativeGetFrameAtTime(handle: Long, timeUs: Long): Bitmap?

@Keep

@JvmStatic

private external fun nativeGetFrameAtIndex(handle: Long, frameIndex: Int): Bitmap?

@Keep

@JvmStatic

private external fun nativeGetRotationDegrees(handle: Long): Int

@Keep

@JvmStatic

private external fun nativeRelease(handle: Long)

Copilot · 2026-02-19T16:18:38Z

mediainfo/src/main/cpp/media_thumbnail_retriever.cpp

+static jobject create_bitmap(JNIEnv *env, int width, int height) {
+    jclass bitmapClass = env->FindClass("android/graphics/Bitmap");
+    if (!bitmapClass) {
+        return nullptr;
+    }
+
+    jclass bitmapConfigClass = env->FindClass("android/graphics/Bitmap$Config");
+    if (!bitmapConfigClass) {
+        return nullptr;
+    }
+
+    jfieldID argb8888Field = env->GetStaticFieldID(
+            bitmapConfigClass,
+            "ARGB_8888",
+            "Landroid/graphics/Bitmap$Config;");
+    if (!argb8888Field) {
+        return nullptr;
+    }
+
+    jobject argb8888Obj = env->GetStaticObjectField(bitmapConfigClass, argb8888Field);
+    if (!argb8888Obj) {
+        return nullptr;
+    }
+
+    jmethodID createBitmapMethod = env->GetStaticMethodID(
+            bitmapClass,
+            "createBitmap",
+            "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
+    if (!createBitmapMethod) {
+        return nullptr;
+    }
+
+    return env->CallStaticObjectMethod(bitmapClass, createBitmapMethod, width, height, argb8888Obj);
+}


Potential JNI local reference leak. When create_bitmap fails to find classes, get field IDs, or call methods, the function returns nullptr without deleting previously created local references (bitmapClass, bitmapConfigClass, argb8888Obj). While these will be cleaned up when the JNI frame ends, it's better practice to explicitly delete them or use DeleteLocalRef to avoid accumulating references in loops or long-running operations.

Copilot · 2026-02-19T16:18:38Z

mediainfo/src/main/cpp/media_thumbnail_retriever.cpp

+        AVStream *stream = formatContext->streams[i];
+        if (stream->codecpar->codec_type != AVMEDIA_TYPE_VIDEO) {


Missing null check for AVStream. After retrieving the stream at line 310, the code dereferences stream->codecpar without verifying that stream is not null. While unlikely in practice, this could cause a crash if nb_streams is inconsistent with the actual streams array.

Copilot · 2026-02-19T16:18:38Z

mediainfo/src/main/cpp/media_thumbnail_retriever.cpp

+        return nullptr;
+    }
+
+    av_seek_frame(context->formatContext, context->videoStreamIndex, 0, AVSEEK_FLAG_BACKWARD);


The return value of av_seek_frame is not checked. While the subsequent avcodec_flush_buffers and decode operations may still work, ignoring seek failures could lead to unexpected behavior. Consider checking the return value and handling seek failures appropriately, similar to how decode_frame_at_time handles it.

Suggested change

av_seek_frame(context->formatContext, context->videoStreamIndex, 0, AVSEEK_FLAG_BACKWARD);

int seekResult = av_seek_frame(context->formatContext, context->videoStreamIndex, 0, AVSEEK_FLAG_BACKWARD);

if (seekResult < 0) {

avcodec_free_context(&codecContext);

return nullptr;

}

anilbeesetti added 3 commits February 8, 2026 11:45

add thumbnail retriever class

8e6d052

fix thumbnail rotation

93f5057

refine api

78ecab4

anilbeesetti requested a review from Copilot February 19, 2026 16:09

Copilot started reviewing on behalf of anilbeesetti February 19, 2026 16:09 View session

Copilot AI reviewed Feb 19, 2026

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Media thumbnail retriever#168

Media thumbnail retriever#168
anilbeesetti wants to merge 3 commits intomainfrom
media-thumbnail-retriever

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-    av_seek_frame(context->formatContext, context->videoStreamIndex, targetTimestamp, AVSEEK_FLAG_BACKWARD);
+    int seekResult = av_seek_frame(context->formatContext, context->videoStreamIndex, targetTimestamp, AVSEEK_FLAG_BACKWARD);
+    if (seekResult < 0) {
+        // Failed to seek to the requested timestamp; clean up and return null.
+        avcodec_free_context(&codecContext);
+        return nullptr;
+    }

		AVStream *stream = formatContext->streams[i];
		if (stream->codecpar->codec_type != AVMEDIA_TYPE_VIDEO) {

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