这个问题的原因主要是因为UDP视频流中缺少PTS信息，而ExoPlayer默认使用PTS信息来更新时间轴位置。因此，我们需要手动更新时间轴位置以适应这个问题。

我们可以通过实现自定义MediaSource和TrackRenderer来手动更新时间轴位置。首先，我们需要在我们的应用程序中创建自定义TrackRenderer，它会定期检查当前播放时间和待播放时间，并将其发送给ExoPlayer进行更新。

以下是一个示例：

public class CustomTrackRenderer extends TrackRenderer {
    private static final long UPDATE_INTERVAL_MS = 1000L;
    
    private final Handler mHandler = new Handler();
    private final Runnable mUpdateTimeTask = new Runnable() {
        @Override
        public void run() {
            if (getState() == TrackRenderer.STATE_STARTED) {
                long currentPositionMs = getCurrentPositionUs() / 1000L;
                long durationMs = getDurationUs() / 1000L;
                if (durationMs <= 0 || currentPositionMs > durationMs) {
                    currentPositionMs = durationMs;
                }
                mPlayer.sendMessage(mPlayer.obtainMessage(MSG_SET_PLAYBACK_PARAMS, currentPositionMs, durationMs));
            }
            mHandler.postDelayed(mUpdateTimeTask, UPDATE_INTERVAL_MS);
        }
    };
    
    private ExoPlayer mPlayer;
    
    public CustomTrackRenderer(Handler eventHandler, Callback callback) {
        super(eventHandler, callback);
    }
    
    @Override
    protected void onEnabled(int track, long positionUs, boolean joining) {
        mHandler.post(mUpdateTimeTask);
    }
    
    @Override
    protected void onDisabled() {
        mHandler.removeCallbacks(mUpdateTimeTask);
    }
    
    @Override
    protected void onStarted() {
        mHandler.post(mUpdateTimeTask);
    }
    
    @Override
    protected void onStopped() {
        mHandler.removeCallbacks(mUpdateTimeTask);
    }
    
    @Override
    protected void onReleased() {
        mHandler.removeCallbacks(mUpdateTimeTask);
    }
    
    @Override
    protected void onSeekTo(long timeUs) {
    }
    
    @Override
    protected void onStarted(long positionUs) {
        mHandler.post(mUpdateTimeTask);
    }
    
    @Override
    protected void onStopped(long positionUs, boolean joining) {
        mHandler.removeCallbacks(mUpdateTimeTask);
    }
    
    @Override
    public void handleMessage(int messageType, Object message) throws ExoPlaybackException {
        switch (messageType) {
            case MSG_SET_PLAYER:
                mPlayer = (ExoPlayer) message;
                break;
            default:
                super.handle