使用MediaCodec对本地mp4视频进行帧预览, 区间选择,

实现说明

1. 使用的播放器为原生MediaPlayer, 所以在帧选择时可能不太流畅, 在高于O版本的手机上会好一点, 这是因为如下的一个新接口:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            player.seekTo(startMillSec, SEEK_CLOSEST)
        } else {
            player.seekTo(startMillSec.toInt())
        }

最开始的时候用的是Exoplayer2, 效果竟然还没有MediaPlayer好, 有点不可思议.
公司项目用的是腾讯视频sdk, 效果好很多, 但是需要一大堆依赖. 猜测它应该是使用的ffmpeg实现的.

如果要实现最流畅的预览效果, 需要重新生成一个关键帧丰富的视频文件. 这是一个可以折中放弃的选项.

3. 慢速, 快速播放. 目前MediaPlayer, exoPlayer2已经支持.

4. 缩略图使用的TextureView截图实现, 虽然笨拙且慢, 但是目前在不依赖ffmpeg情况下, 这是最保险的. 因为对于关键帧确实的视频extractor也无法抓取到正确的图像.
   具体可以参看: https://www.jianshu.com/p/0f6578362e58

5. 其实最费劲的是怎么计算帧选择时, 以及裁剪区间时的时间点. 可费劲了. 这也是我决定放到github上的原因, 万一以后还会用到呢. 不想再折腾一次了.

6. 支持裁剪. 具体代码:

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public static boolean genVideoUsingMuxer(Context context, String srcPath, String dstPath,
                                           int startMs, int endMs, boolean useAudio, boolean
                                                   useVideo)
            throws IOException {
        boolean success = true;
        // Set up MediaExtractor to read from the source.
        MediaExtractor extractor = new MediaExtractor();
        extractor.setDataSource(srcPath);
        int trackCount = extractor.getTrackCount();
        // Set up MediaMuxer for the destination.
        MediaMuxer muxer;
        muxer = new MediaMuxer(dstPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);
        // Set up the tracks and retrieve the max buffer size for selected
        // tracks.
        HashMap<Integer, Integer> indexMap = new HashMap<>(trackCount);
        int bufferSize = -1;
        for (int i = 0; i < trackCount; i++) {
            MediaFormat format = extractor.getTrackFormat(i);
            String mime = format.getString(MediaFormat.KEY_MIME);
            boolean selectCurrentTrack = false;
            if (mime.startsWith("audio/") && useAudio) {
                selectCurrentTrack = true;
            } else if (mime.startsWith("video/") && useVideo) {
                selectCurrentTrack = true;
            }
            if (selectCurrentTrack) {
                extractor.selectTrack(i);
                int dstIndex = muxer.addTrack(format);
                indexMap.put(i, dstIndex);
                if (format.containsKey(MediaFormat.KEY_MAX_INPUT_SIZE)) {
                    int newSize = format.getInteger(MediaFormat.KEY_MAX_INPUT_SIZE);
                    bufferSize = newSize > bufferSize ? newSize : bufferSize;
                }
            }
        }

        if (bufferSize < 0) {
            bufferSize = 1080*1920*30; // todo
        }

        // Set up the orientation and starting time for extractor.
        MediaMetadataRetriever retrieverSrc = new MediaMetadataRetriever();
        retrieverSrc.setDataSource(srcPath);
        String degreesString = retrieverSrc.extractMetadata(
                MediaMetadataRetriever.METADATA_KEY_VIDEO_ROTATION);
        if (degreesString != null) {
            int degrees = Integer.parseInt(degreesString);
            if (degrees >= 0) {
                muxer.setOrientationHint(degrees);
            }
        }
        if (startMs > 0) {
            extractor.seekTo(startMs * 1000, MediaExtractor.SEEK_TO_PREVIOUS_SYNC);
        }
        // Copy the samples from MediaExtractor to MediaMuxer. We will loop
        // for copying each sample and stop when we get to the end of the source
        // file or exceed the end time of the trimming.
        int offset = 0;
        int trackIndex = -1;
        ByteBuffer dstBuf = ByteBuffer.allocate(bufferSize);
        MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
        try {
            muxer.start();
            while (true) {
                bufferInfo.offset = offset;
                bufferInfo.size = extractor.readSampleData(dstBuf, offset);
                if (bufferInfo.size < 0) {
                    Log.d(TAG, "Saw input EOS.");
                    bufferInfo.size = 0;
                    break;
                } else {
                    bufferInfo.presentationTimeUs = extractor.getSampleTime();
                    if (endMs > 0 && bufferInfo.presentationTimeUs > (endMs * 1000)) {
                        Log.d(TAG, "The current sample is over the trim end time.");
                        break;
                    } else {
                        bufferInfo.flags = extractor.getSampleFlags();
                        trackIndex = extractor.getSampleTrackIndex();
                        muxer.writeSampleData(indexMap.get(trackIndex), dstBuf,
                                bufferInfo);
                        extractor.advance();
                    }
                }
            }
            muxer.stop();

            //deleting the old file
//            File file = new File(srcPath);
//            file.delete();
        } catch (Exception e) {
            // Swallow the exception due to malformed source.
            Log.w(TAG, "The source video file is malformed");
            success = false;
        } finally {
            muxer.release();
        }
        return success;
    }

代码位置: https://github.com/shaopx/VideoClipEditViewTest