On date Sunday 2011-07-24 04:51:49 -0400, Matthew Einhorn encoded: > Hi, > > I'm using the ffmpeg API to decode videos and I ran into two issues > while using it. > > 1. I'm decoding by calling in a loop av_read_frame followed by > avcodec_decode_video2 and if frameFinished I then use sws_scale to > convert from my source format to dest format. This work fine for all > videos except pal8 videos. For pal8, sws_scale results in a completely > black picture. I suspected that the pal8 palette must be massed up and > indeed the palette returned by avcodec_decode_video2 is all zero.
If the problem is the source image, you should check that the palette in data[1] provided to libswscale is correct (e.g. you can check that it is different from 0). Also check if the ff* tools can deal with the file correctly. If not a sample program / sample test showing the problem may be useful. > In particular, from what I seemed to have read and seen of ffmpeg, for > pal8 AVFrame data[0] is the data, while data[1] is the palette. When > calling avcodec_decode_video2 on a pal8 video, data[0] is indeed data > (bunch of different values), while data[1] is an array with all > elements zero. Indeed, when I edited data[1] to some random values the > sws_scale output image was not black anymore and you could see the > remnants of my picture. > > So I'm wondering, is the video file broken and that's why the palette > doesn't show up? Or did I miss a flag when initializing codec/format > context etc. so that the palette isn't read? AFAIK you don't need any special hacks for working with palette formats. > 2. I'm looking for a function similar to avcodec_find_best_pix_fmt. > What I want is to pass in a list of formats and the function would > return what's the closest format. For example, say the source format > is pal8 and I pass in as possible destination formats: RGB24 and > GRAY8. Then the function should return GRAY8. > avcodec_find_best_pix_fmt would return in that case RGB24 which "is" > the best format, but in this case would waste 2 extra bytes since pal8 > is only 8 bytes depth and gray to start with. > > Does a function like this exist? Would it be easy for me to write such > a function using the ffmpeg API? And if so can I get some pointers? Should be easy to hack the logic of avcodec_find_best_pix_fmt() for implementing an avcodec_find_closest_pix_fmt() or such. > Thanks in advance for any help, _______________________________________________ Libav-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/libav-user
