Potential Memory Leak in libmpv Render Context with GPU Hardware Decoding (Qt OpenGLWidget)

[dingph]

Hello,

I'm using the libmpv library for video playback within a Qt application. I have encountered a consistent memory leak issue starting from the specific build mpv-dev-x86_64-v3-20250302-git-ee07dcf.7z (dated March 2, 2025) and later versions. The problem does not occur in builds prior to this date.

Reproduction Steps:

Initialize mpv (mpv_create()) and set properties to use GPU hardware decoding (hwdec=auto-safe or similar).

Initialize an OpenGL render context using mpv_render_context_create() with parameters for OpenGL backend and Qt integration.

Render video frames using mpv_render_context_render() onto a Qt QOpenGLWidget.

Play either an RTSP stream or a local video file.

Observe a steady increase in the application's memory usage (RAM) over time during playback. The memory does not get freed even after stopping playback or closing the video file. The leak appears to be proportional to playback duration.

My Environment:

libmpv Version: mpv-dev-x86_64-v3-20250302-git-ee07dcf.7z (and later 2025 builds). Previous builds (e.g., from February 2025) are fine.

System: Windows 10/11, x86_64.

Graphics: NVIDIA discrete GPU (tested with RTX series).

Backend: OpenGL.

Rendering Widget: Qt QOpenGLWidget.

Playback Source: Both RTSP streams and local video files trigger the leak.

[kasper93]

Probably related to #17217

[kasper93]

mpv-dev-x86_64-v3-20250302-git-ee07dcf.7z (dated March 2, 2025) and later versions. The problem does not occur in builds prior to this date.

Which one is previous build, you have tested? I would assume mpv-dev-x86_64-v3-20250216-git-f94b44c.7z? So the range of commits would be f94b44c...ee07dcf correct?

If earlier build, there is another change, but please confirm which builds your are testing.

[dingph]

Hello,
you are right, This narrows the introducing commit to between f94b44c (2025-02-16) and ee07dcf (2025-03-02).

I am using the libmpv library for video playback within a Qt application (QOpenGLWidget) and have confirmed a memory leak regression that was introduced in builds starting from early March 2025.


1. Summary of the Bug
   
   When using GPU hardware decoding (hwdec) with the OpenGL render context, the application's memory (RAM) increases steadily during playback and is not freed after stopping.
   
   The leak occurs with both RTSP streams and local files.
   
   Crucially, this is a regression. The leak does not exist in builds from February 2025 and earlier.
   
2. Exact Versions Tested (This is key for bisecting)
   I have conducted binary testing with the following official dev builds:
   
   LEAKING VERSIONS (The regression starts here):
   
   mpv-dev-x86_64-v3-20250302-git-ee07dcf.7z
   
   mpv-dev-x86_64-v3-20250309-git-edf4fdf.7z
   
   mpv-dev-x86_64-v3-20250608-git-a418d21.7z
   
   CLEAN VERSIONS (No leak):
   
   mpv-dev-x86_64-v3-20250216-git-f94b44c.7z
   
   mpv-dev-x86_64-v3-20250209-git-e4b64fb.7z
   
   mpv-dev-x86_64-v3-20230129-git-86093fc.7z
   
   
   
   

[kasper93]

Should be fixed by #17303, see #17217 for more info.