Everybody is good, I ask you, use a webcam manufacturer SDK, can normal real-time access to the I frame from the callback function, P frame data, use ffmpeg decode these frame P frame, I now also normal decoding, and then turn the decoded data YUV format saved BMP images, including the I frame picture looks normal, but most parts of the P frame can see changes of gray, after inquire on the net, probably mean P frame decoding only difference data, can't restore full image, need to decode with reference frame, according to the hints I tried various combinations: P frame plus I frame data decoding, or after the I frame decoder YUV data preservation and P frame after the decoding function, can restore normal P frame picture, to ask you, have done P frame decoding reconstruction images, please comment, thank you!