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Possible bug with av_frame_get_buffer() when trying to get audio frame buffer #50
Description
Using FFmpeg version 7.1, though I did test with 7.0 and it persisted there as well.
The upper half of this snippet always fails with the EINVAL error return code, despite the fact that the frame has the nb_samples, ch_layout, and sample_format fields set, which should be all that is required to allocate the buffers according to the documentation.. I have looked over the libav source code and manually tried the checks that can return EINVAL, and this setup shouldn't be tripping them as far as I can tell. The video frame buffer get is there as a sanity check and it works exactly as expected.
Addendum: I finally managed to make a C project to test this, and have confirmed that it works fine in raw C. This code should be equivalent to the C# code:
This correctly returns 0 and allocates the buffers, whereas the C# code has the previously described error.
Activity
zgabi commentedon Jan 18, 2025
I got 0:
I'm using ffmpeg 7.0.1, from gyan.dev:
ffmpeg-7.0.1-full_build-shared.7z
After upgrade to 7.1 it still works. So probaby you are using a "wrong" ffmpeg version. From where did you download id?
Error-String-Expected-Got-Nil commentedon Jan 19, 2025
After MUCH investigation I figured out what the problem was.
In my use-case, I am running a 32-bit process (I'm making a video encoder I intend to build into a mod for a Unity game, which is 32 bit). The
AVFramestruct in C/direct libav has 4 fields of typesize_t, which is an unsigned integer type who's size is system/platform-dependent, as it has a size of 8 bytes in 64 bit, and 4 bytes on 32 bit.The
AVFramestruct in FFmpeg.AutoGen, however, just usesulongs for these fields. Thus, when accessing the fields of theAVFramein C#, there is a serious misalignment of their locations in memory, making writes and reads to certain fields go to the wrong locations. None of the affected fields are relevant for video frames (as only fields sequentially below thesize_tfields are affected), but they are relevant for audio frames.I made my own version of the
AVFramestruct in C# usinguints instead ofulongs for these fields, and with some pointer casts, it proceeded to work exactly as expected.I'm not sure if there's a good library-side solution for this, I don't think there's a way to make the type of some field depend on whether the process is 32 or 64 bit. But at least the issue is clear now.