On 11/9/2024 12:55 PM, Pavel Koshevoy wrote:
On Sat, Nov 9, 2024 at 6:22 AM James Almer <jamr...@gmail.com> wrote:On 11/9/2024 1:40 AM, Pavel Koshevoy wrote:On Fri, Nov 8, 2024 at 7:29 PM James Almer <jamr...@gmail.com> wrote:On 11/8/2024 10:51 PM, Pavel Koshevoy wrote:I ran into segfaults in zimg when I attempted to use zscale to convert a 512x538@yuv444p16le(tv) image from HLG to Bt.709 with this filter chain:buffer=width=512:height=538:pix_fmt=yuv444p16le:time_base=1/1:sar=1/1,zscale=min=2020_ncl:rin=limited:pin=2020:tin=arib-std-b67:cin=left:t=linear,format=gbrpf32le,tonemap=gamma:desat=0,zscale=tin=linear:npl=100:p=709:m=709:r=limited:t=709,format=pix_fmts=yuv444p16le,buffersinkI found several issues: - realign_frame called av_pix_fmt_count_planes with incorrectparameter.- av_frame_get_buffer did not align data pointers to specifiedalignment.Because it's not supposed to. The align parameter doxy states "buffer size alignment", which is the result of aligning the stride/linesizes, not the data pointers. You may want to use ff_default_get_video_buffer2(), which will add align amount of bytes to the allocated buffers (On top of aligning the linesizes to it), and then align the pointers with FFALIGN().I am not the maintainer of vf_zscale, and I am not intimately familiarwithprivate ffmpeg APIs such as ff_default_get_video_buffer2, and at first glance that function doesn't appear to be a drop-in replacement for av_frame_get_buffer. ff_default_get_video_buffer2 requires AVFilterLink parameter?! -- realign_frame doesn't have that, it has an AVFrame which it needs to re-align to make it compatible with libzimg API.It's trivial to make realign_frame take the necessary AVFilterLink as input argument.... and why isn't av_frame_get_buffer populating AVFrame.data pointers aligned as specified by the align parameter? It costs at most (align - 1) more padding bytes to make it align the pointers, so I don't understand why it doesn't dothat. Buffer alignment is set at configure time. It will be set to the highest needed alignment for the enabled simd (64 if avx512, else 32 if avx, else 16 if neon/sse, else 8). This is handled by av_malloc(), which is ultimately used by all alloc functions.Yes, I have noticed this while stepping through ffmpeg and zimg code. The surprising thing I've observed is that ff_get_cpu_max_align_x86() (called from av_cpu_max_align()) returned 8 ... it's surprising for an ffmpeg built and running on a Ryzen R9 5950x -- I would have expected 32.
Yeah, av_cpu_max_align() returns a value depending on runtime parameters, so unless you force cpuflags using av_force_cpu_flags() to disable everything SSE and above (or it being disabled during configure), it should not return 8.
As a side note ... this ffmpeg build (and zimg build) were produced by conan, so perhaps the conan recipe for ffmpeg needs some changes to make av_cpu_max_align() work as expected on 5950x. (https://conan.io/center/recipes/ffmpeg)
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