On Thu, Jul 28, 2011 at 8:15 AM, Matthew Einhorn <[email protected]> wrote: > 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 >
FYI this seems to have been fixed in one of the recent gits. Thanks, Matt _______________________________________________ Libav-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/libav-user
