Problems with MediaExtractor

问题:

I am trying to get specific frames at specific times as images from a movie using MediaExtractor and MediaCodec. I can do it successfully if:

• I use extractor.seekTo(time, MediaExtractor.SEEK_TO_PREVIOUS_SYNC); , however, this only gives the nearest sync frame not the target frame.
• I sequentially extract all frames using extractor.advance(); , but I need to get the target frame not all.

So, I try the following:

extractor.seekTo(time, MediaExtractor.SEEK_TO_PREVIOUS_SYNC);
while(extractor.getSampleTime()<time /*target time*/) extractor.advance();

This provides the correct frame, but for some reason the image is corrupted. It looks like the correct image (the one I get from the successful cases), but with some pixelation and a strange haze.

The while-loop is the only thing that is different between the successful cases and the corrupted ones. What to do to advance MediaExtractor to a specific time (not just sync time) without getting a corrupted image?

回答1:

Thanks to fadden comment, I have to keep feeding the encoder since the I-frame has the full picture and the P and B frames have differences (this is how compression is achieved). So I need to start with an I-frame (it was same as sync frame) and keep feeding the other frames to the decoder to receive the full image.