VLC plays an mp4 but mpv doesn't

I have videos that I have ripped off a streaming site, the vast majority play with mpv.

One or two, I get the error:

[ffmpeg/demuxer] mov,mp4,m4a,3gp,3g2,mj2: Invalid sample size -3
[ffmpeg/demuxer] mov,mp4,m4a,3gp,3g2,mj2: error reading header
[lavf] avformat_open_input() failed
[ffmpeg/demuxer] mov,mp4,m4a,3gp,3g2,mj2: Invalid sample size -3
[ffmpeg/demuxer] mov,mp4,m4a,3gp,3g2,mj2: error reading header
[lavf] avformat_open_input() failed
Failed to recognize file format

If I fire up VLC, I get:

avcodec decoder: Using Intel i965 driver for Intel(R) Sandybridge Mobile - 2.4.0 for hardware decoding

And all is good.

Is this an ffmpeg issue?. Does anyone have any ideas how I can fix this?

Video drivers/ffmpeg is well beyond me.

ffmpeg version 4.2.4-1ubuntu0.1 Copyright (c) 2000-2020 the FFmpeg developers built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)

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