Re: [FFmpeg-devel] [PATCH] fftools/cmdutils: add an option to append to the report file

[James Almer <jamrial@gmail.com>]

On 2/1/2022 8:58 AM, Dan Zwell wrote:
> There are times when we want ffmpeg to log, but we don't want it to
> overwrite the log file. In addition to the use case described in the
> ticket, a third party tool that invokes ffmpeg may write additional
> information to the log file, such as why the encoding options were
> chosen.
> 
> This implements:
> https://trac.ffmpeg.org/ticket/3059
> 
> Note: unknown keys are ignored, so adding a new "append" key does not
> break backward compatibility.
> 
> Signed-off-by: Dan Zwell <devel@zwell.net>
> ---
>   doc/fftools-common-opts.texi | 3 +++
>   fftools/cmdutils.c           | 8 +++++++-
>   2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/fftools-common-opts.texi b/doc/fftools-common-opts.texi
> index d9145704d6..4c6c297315 100644
> --- a/doc/fftools-common-opts.texi
> +++ b/doc/fftools-common-opts.texi
> @@ -270,6 +270,9 @@ of the program, @code{%t} is expanded to a 
> timestamp, @code{%%} is expanded
>   to a plain @code{%}
>   @item level
>   set the log verbosity level using a numerical value (see 
> @code{-loglevel}).
> +@item append
> +@code{append=1} tells ffmpeg to append to a report file if it exists 
> instead
> +of overwriting it.

Maybe "A non zero value", since it will work with more than just 1.
Alternatively, you can check for the argument and error out on anything 
but 0 or 1.

>   @end table
>    For example, to output a report to a file named @file{ffreport.log}
> diff --git a/fftools/cmdutils.c b/fftools/cmdutils.c
> index 4b50e15eef..350329ee8b 100644
> --- a/fftools/cmdutils.c
> +++ b/fftools/cmdutils.c
> @@ -983,6 +983,7 @@ static int init_report(const char *env)
>       time_t now;
>       struct tm *tm;
>       AVBPrint filename;
> +    int append = 0;
>        if (report_file) /* already opened */
>           return 0;
> @@ -1012,6 +1013,8 @@ static int init_report(const char *env)
>                   exit_program(1);
>               }
>               envlevel = 1;
> +        } else if (!strcmp(key, "append")) {
> +            append = strtol(val, NULL, 10);

Don't silently ignore invalid arguments. See how level is handled above.

>           } else {
>               av_log(NULL, AV_LOG_ERROR, "Unknown key '%s' in 
> FFREPORT\n", key);
>           }
> @@ -1032,7 +1035,10 @@ static int init_report(const char *env)
>       if (!envlevel)
>           report_file_level = FFMAX(report_file_level, prog_loglevel);
>   -    report_file = fopen(filename.str, "w");
> +    if (append)
> +        report_file = fopen(filename.str, "a");
> +    else
> +        report_file = fopen(filename.str, "w");
>       if (!report_file) {
>           int ret = AVERROR(errno);
>           av_log(NULL, AV_LOG_ERROR, "Failed to open report \"%s\": %s\n",
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