On Thu, Jul 28, 2011 at 6:02 AM, Stefano Sabatini <[email protected]> wrote: > On date Tuesday 2011-07-26 13:58:00 -0400, Matthew Einhorn encoded: >> On Sun, Jul 24, 2011 at 9:41 AM, Stefano Sabatini >> <[email protected]> wrote: >> > On date Sunday 2011-07-24 04:51:49 -0400, Matthew Einhorn encoded: > [...] >> Upon spending some time with the debugger I've isolated the problem >> into a very weird corner. But first a bit more about my code (partly >> attached). My code is a dll wrapper to the ffmpeg dlls. Upon one dll >> call you create an object for a video and initialize all the >> format/conversion/codec contexts (open function). Then with further >> dll calls you request the next frame. As said, this works fine now for >> all video formats I tested with except pal8 (rawvideo). With pal8, >> calling avcodec_decode_video2(m_pCodecCtx, m_pFrame, &nFrameFinished, >> m_pAVPacket) copies a palette of zero into m_pFrame->data[1] >> (palette_has_changed is also zero). So this has nothing to do with the >> sws_scale, because sws_scale gets a bad palette. So the question is >> why avcodec_decode_video2 doesn't read the palette. The video file >> isn't bad because of the following. > > So far so good. > >> I was able to fix this if before returning from the open function I >> added one call to avcodec_decode_video2 (and of course before that to >> av_read_frame). That is, if I asked ffmpeg to decode the first frame >> before I returned from the function that initialized frames, context >> etc. the palette was read correctly in the first and subsequent frames >> (palette_has_changed was one). But if I requested the first frame >> after returning from my open frame function, in a separate function, >> the palette isn't read properly. >> >> Now, this smells of something going out of context and closed when my >> open function returns. It cannot be my variables because all of my >> variables are created as class variables beforehand which stay put. I >> also don't use any smart pointers or such. So it must be (I think) >> that one of the av alloc functions clears something if I don't decode >> a frame before returning from the function that called the av alloc >> function. I think it's something with the decoder, possibly a buffer? >> >> My dlls are called from the same thread every time they are called and >> the dll doesn't unload or move between calls. Now ffplay does all its >> work from one central main function with calls to other functions (and >> it's not a dll) so that's why I think ffplay doesn't have an issue >> with it. >> > >> Now, I understand that this might be difficult to debug so I'm mostly >> asking for clues and what to look at. I.e. in all the format/codec >> contexts structs is there some function pointer or member variables >> that are responsible for getting the palettes and will help me track >> down the issue? > > Why the > av_free_packet(m_pAVPacket); > > in cDecodeFrame()? > > This looks suspicious. >
The reason for the av_free_packet call after decoding the frame is that that's how the dranger example did it. But ffplay also does the same thing at line 1773: http://www.ffmpeg.org/doxygen/trunk/ffplay_8c-source.html#l01771 When I removed the av_free_packet call it introduced a memory leak into the application and the memory use of the app grew with each call to get next frame and it also didn't fix the pal8 palette issue. >> avcodec_decode_video2 ends up calling some function >> pointer so I couldn't follow through the code to see where it's >> actually read. It could also be that the problem is with the the >> zeranoe dlls in which case this might not be the best place to solve >> it, but I doubt it because it works fine for all the other videos. >> >> >> >> 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. >> > >> >> I looked through the code for the above functions and I think as is, >> the avcodec_find_best_pix_fmt function should return the closest pix >> format like I want. I think the only reason it doesn't (I think) is >> because the pal8 format in particular might be set wrongly. >> > >> If you look at the pix_fmt_info array that the >> avcodec_find_best_pix_fmt1 func is referring to, you'll see this >> definition for pal8: >> [PIX_FMT_PAL8] = { >> .is_alpha = 1, >> .color_type = FF_COLOR_RGB, >> .depth = 8, >> }, >> >> shouldn't it be .color_type = FF_COLOR_GRAY? Because it's set to >> FF_COLOR_RGB, the avcodec get loss function returns a chroma and >> colorspace loss when converting from pal8 to gray8. That's why RGB24 >> gets picked over gray8. But I thought that pal8 is already gray (B/W) >> so there shouldn't be any loss? Admittedly, I don't know too much >> about the pix formats. > > Pal8 works by storing a palette in data[1], which maps an integer in > the range 0-255 to an RGBA 32-bits entry. > > The actual chromatic image features can be guessed only by analyzing > the palette itself, in case you have all the RGBA entries set to a > gray color then it will be gray, but in general a PAL8 image will > contain a colored (R != G != B) data. > I didn't know that. The pal8 videos I saw was gray so I assumed all of them were (although if they were all gray a palette wouldn't really be needed...). So avcodec_find_best_pix_fmt should work fine for me then. Thanks, Matt _______________________________________________ Libav-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/libav-user
