Extract thumbnail on mp4

[pierrexn]

Try to extract thumbnail on this .mp4 (Windows x64)

In the callback for p.prepare, p.seek return true but callbakc for p.onFrame is never called

https://github.com/wang-bin/mdk-sdk/assets/1200371/5fee6721-f7d6-40b6-83b2-6be7a14828fb

[feiyangqingyun]

这个文件估计有问题，用vlc或者ffplay播放都是没有任何画面，只有声音。

[wang-bin]

Because no video track in this file. Thumbnail example works as expected

[pierrexn]

i use the code that you have sent me

p.prepare(from, [&](int64_t pos, bool*) {
            if ((pos < 0 || p.mediaInfo().video.empty() && test_flag(p.mediaStatus(), mdk::MediaStatus::Loaded)))
                pm.set_value(-2);
            else
            {
                auto ret = p.seek((p.mediaInfo().duration * video_frame_percent) / 100
                    , mdk::SeekFlag::FromStart | mdk::SeekFlag::KeyFrame | mdk::SeekFlag::Backward // KeyFrame: thumbnail should be fast. backward: avoid EPERM error
                    , [&](int64_t pos) {
                        if (pos < 0 && test_flag(p.mediaStatus(), mdk::MediaStatus::Loaded)) { // check loaded: unfinished seek callback
                            pm.set_value(-3);
                        }
                    });
                if (ret == 0)
                    pm.set_value(-1);
            }
            return true;
        });

As i see in Thumbnail example, you have no more test_flag(p.mediaStatus(), mdk::MediaStatus::Loaded)

[wang-bin]

the example is updated: https://github.com/wang-bin/mdk-examples/blob/master/Native/Thumbnail.cpp

[pierrexn]

Thanks with updated code, it seems to work...