[FFmpeg-devel] [PATCH] fftools/ffmpeg_mux: keep write_header and write_packet in the same thread

[Zhao Zhili]

> On Nov 1, 2023, at 17:01, angus.chen-at-intel.com at ffmpeg.org wrote:
> 
> From: "Chen, Angus" <angus.chen at intel.com>
> 
> sdl2_muxer(wayland):
> In ffmpeg6, we create a separate thread for muxer after calling avformat_write_header().
> It may generate EGL_BAD_ACCESS when we call write_packet. This is because egl_context
> is bound to previous thread.
> From EGL spec: If ctx is current to some other thread, or if either draw or read are
> bound to contexts in another thread, an EGL_BAD_ACCESS error is generated.

As I replied in

https://patchwork.ffmpeg.org/project/ffmpeg/patch/20230918063728.198377-1-haihao.xiang@intel.com/

The patch only works on some platforms. SDL should run in main thread.

I don’t think it can be fixed at here.

There are at least two methods:
1. Use ffmpeg main thread to handle special tasks like this.
2. Give up and suggests user to pipe ffmpeg output to ffplay, or something like this.

> 
> Signed-off-by: Chen, Angus <angus.chen at intel.com>
> ---
> fftools/ffmpeg_mux.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/fftools/ffmpeg_mux.c b/fftools/ffmpeg_mux.c
> index 7a924dba6c..d9eee3bb6d 100644
> --- a/fftools/ffmpeg_mux.c
> +++ b/fftools/ffmpeg_mux.c
> @@ -215,12 +215,21 @@ static void *muxer_thread(void *arg)
>     OutputFile *of = &mux->of;
>     AVPacket  *pkt = NULL;
>     int        ret = 0;
> +    AVFormatContext *fc = mux->fc;
> 
>     pkt = av_packet_alloc();
>     if (!pkt) {
>         ret = AVERROR(ENOMEM);
>         goto finish;
>     }
> +    ret = avformat_write_header(fc, &mux->opts);
> +    if (ret < 0) {
> +        av_log(mux, AV_LOG_ERROR, "Could not write header (incorrect codec "
> +               "parameters ?): %s\n", av_err2str(ret));
> +        goto finish;
> +    }
> +    //assert_avoptions(of->opts);
> +    mux->header_written = 1;
> 
>     thread_set_name(of);
> 
> @@ -599,15 +608,6 @@ int mux_check_init(Muxer *mux)
>             return 0;
>     }
> 
> -    ret = avformat_write_header(fc, &mux->opts);
> -    if (ret < 0) {
> -        av_log(mux, AV_LOG_ERROR, "Could not write header (incorrect codec "
> -               "parameters ?): %s\n", av_err2str(ret));
> -        return ret;
> -    }
> -    //assert_avoptions(of->opts);
> -    mux->header_written = 1;
> -
>     av_dump_format(fc, of->index, fc->url, 1);
>     nb_output_dumped++;
> 
> -- 
> 2.29.0
> 
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