[FFmpeg-devel] [RFC]lavu/timecode: Increase AV_TIMECODE_STR_SIZE.

[Aaron Levinson]

On 5/5/2017 12:20 AM, Carl Eugen Hoyos wrote:
> 2017-05-05 3:29 GMT+02:00 Aaron Levinson <alevinsn at aracnet.com>:
>> On 5/4/2017 4:27 PM, Carl Eugen Hoyos wrote:
>>>
>>> Hi!
>>>
>>> Attached patch is one possibility to fix the following warning with gcc 7:
>>> libavutil/timecode.c: In function ‘av_timecode_make_string’:
>>> libavutil/timecode.c:103:60: warning: ‘%02d’ directive output may be
>>> truncated
>>> writing between 2 and 10 bytes into a region of size between 0 and 7
>>> [-Wformat-truncation=]
>>>      snprintf(buf, AV_TIMECODE_STR_SIZE, "%s%02d:%02d:%02d%c%02d",
>>>                                                             ^~~~
>>> libavutil/timecode.c:103:41: note: directive argument in the range [0,
>>> 2147483647]
>>>      snprintf(buf, AV_TIMECODE_STR_SIZE, "%s%02d:%02d:%02d%c%02d",
>>>                                          ^~~~~~~~~~~~~~~~~~~~~~~~
>>> libavutil/timecode.c:103:5: note: ‘snprintf’ output between 12 and 32
>>> bytes
>>> into a destination of size 16
>>>      snprintf(buf, AV_TIMECODE_STR_SIZE, "%s%02d:%02d:%02d%c%02d",
>>>      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>               neg ? "-" : "",
>>>               ~~~~~~~~~~~~~~~
>>>               hh, mm, ss, drop ? ';' : ':', ff);
>>>               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>
>>> Several similar warnings are printed, an alternative is to disable the
>>> warning.
>>>
>>> The warning seemed wrong on first sight but may actually be correct, we
>>> accept invalid fps for timecode.
>>
>>
>> Regarding the change in your patch:
>>
>> -#define AV_TIMECODE_STR_SIZE 16
>> +#define AV_TIMECODE_STR_SIZE 23
>>
>> It seems like 23 characters wouldn't be sufficient based on the warning:
>> "output between 12 and 32 bytes into a destination of size 16".  I would
>> guess that you would need at least 32 characters and perhaps one more (?)
>> for the terminating null character to avoid that warning.
>
> How can I reproduce / test your findings?

#define AV_TIMECODE_STR_SIZE 32 or 33 and confirm that gcc 7 warnings go 
away.

Aaron Levinson