On 2021-03-01 16:43, Mark Filipak (ffmpeg) wrote:
The ffmpeg filter pipeline assigns a 'PTS' to each frame, frame by
frame. Is *that* 'PTS' an int64_t?
I don't know how to answer this question. I don't know of a single piece
of code which is the "ffmpeg filter pipeline". I understand that term to
refer to a collection of design parameters which organises the
interaction of code modules. It is the code modules which store
Presentation Timestamps (PTSs).
It is meaningful, I believe, to ask if the code modules store PTS values
as int64_t types. I believe the answer is generally "yes".
The C++ standards define int64_t as a "signed integer type with width of
exactly… 64 bits… with no padding bits and using 2's complement for
negative values". Source:
https://en.cppreference.com/w/cpp/types/integer . Thus data values of
type int64_t are capable of storing negative integer values.
Things I have found.
https://ffmpeg.org/ffmpeg-filters.html#fps-1
"...trim any frames with a negative PTS."
That implies that PTS can be negative (ergo, is a signed integer).
Yes, I believe that FFmpeg will accept and generate streams which have
negative values for PTS.
http://svn.ffmpeg.org/doxygen/1.0/structAVFrame.html
Is AVFrame the structure of frames in the filter pipeline? If so, then
"int64_t pts
" presentation timestamp in time_base units (time when frame
should be shown to user) If "AV_NOPTS_VALUE then frame_rate =
1/time_base will be assumed."
appears to answer my question, unless it's a different 'frame'...
...What exactly is 'AVFrame'?
I am not sure. I won't try to answer this question.
http://svn.ffmpeg.org/doxygen/1.0/avformat_8h-source.html
"00320 typedef struct AVFrac {
"00321 int64_t val, num, den;
"00322 } AVFrac;"
http://svn.ffmpeg.org/doxygen/1.0/structAVFrac.html#_details
"The exact value of the fractional number is: 'val + num / den'."
That appears to be a definition of something called "PTS" but seems to
not be what's assigned to a frame in the filter pipeline.
That code looks to me like it defines a data type for storing rational
numbers. The copyright notice on that module says year 2001, and
"Fabrice Bellard", the original developer of FFmpeg. That hints that
this module is old code. A mention of PTS there is perhaps a statement
of 20-year-old intentions, rather than a claim about what the current
code does. The fact that the code defines a data type does not say
whether the code actually uses that data type.
The label (name) of what is actually assigned to frames in the filter
pipeline as 'PTS' is unknown to me.
I don't know how to answer this question. See above about the concept of
a "filter pipeline".
Best regards,
—Jim DeLaHunt
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