[FFmpeg-devel] [PATCH] avcodec/setts_bsf: allow to use input stream timebase too

[Andreas Rheinhardt]

Paul B Mahol:
> On Sun, Aug 22, 2021 at 2:48 PM Andreas Rheinhardt <
> andreas.rheinhardt at outlook.com> wrote:
> 
>> Paul B Mahol:
>>> Signed-off-by: Paul B Mahol <onemda at gmail.com>
>>> ---
>>>  doc/bitstream_filters.texi | 5 ++++-
>>>  libavcodec/setts_bsf.c     | 5 ++++-
>>>  2 files changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
>>> index 1900eb4352..b5a0be8ca2 100644
>>> --- a/doc/bitstream_filters.texi
>>> +++ b/doc/bitstream_filters.texi
>>> @@ -777,8 +777,11 @@ The previous output DTS.
>>>  @item PREV_OUTPTS
>>>  The previous output PTS.
>>>
>>> + at item ITB
>>> +The input timebase of stream packet belongs.
>>> +
>>>  @item TB
>>> -The timebase of stream packet belongs.
>>> +The output timebase of stream packet belongs.
>>>
>>>  @item SR
>>>  The sample rate of stream packet belongs.
>>> diff --git a/libavcodec/setts_bsf.c b/libavcodec/setts_bsf.c
>>> index d604f91f71..965c999500 100644
>>> --- a/libavcodec/setts_bsf.c
>>> +++ b/libavcodec/setts_bsf.c
>>> @@ -41,7 +41,8 @@ static const char *const var_names[] = {
>>>      "DTS",         ///< original DTS in the file of the frame
>>>      "STARTPTS",    ///< PTS at start of movie
>>>      "STARTDTS",    ///< DTS at start of movie
>>> -    "TB",          ///< timebase of the stream
>>> +    "ITB",         ///< input timebase of the stream
>>> +    "TB",          ///< output timebase of the stream
>>>      "SR",          ///< sample rate of the stream
>>>      "NOPTS",       ///< The AV_NOPTS_VALUE constant
>>>      NULL
>>> @@ -59,6 +60,7 @@ enum var_name {
>>>      VAR_DTS,
>>>      VAR_STARTPTS,
>>>      VAR_STARTDTS,
>>> +    VAR_ITB,
>>>      VAR_TB,
>>>      VAR_SR,
>>>      VAR_NOPTS,
>>> @@ -154,6 +156,7 @@ static int setts_filter(AVBSFContext *ctx, AVPacket
>> *pkt)
>>>      s->var_values[VAR_PREV_OUTDTS] = s->prev_outdts;
>>>      s->var_values[VAR_STARTPTS]    = s->start_pts;
>>>      s->var_values[VAR_STARTDTS]    = s->start_dts;
>>> +    s->var_values[VAR_ITB]         = ctx->time_base_in.den  ?
>> av_q2d(ctx->time_base_in)  : 0;
>>>      s->var_values[VAR_TB]          = ctx->time_base_out.den ?
>> av_q2d(ctx->time_base_out) : 0;
>>>      s->var_values[VAR_SR]          = ctx->par_in->sample_rate;
>>>
>>>
>> This is of no use: It is the user which sets the input timebase and it
>> is the bsf which (in its init function) chooses the output timebase (the
>> generic bsf code sets it equal to the input timebase and most (all?)
>> filters don't change it). This filter does not change it, so input and
>> output timebases are always equal.
>>
>> The bug in #9382 is really in ffmpeg.c, it can't be fixed in this bsf at
>> all as it lacks the information about the muxing timebase.
>>
> 
> Are you telling me that one field there is now useless?
> Above Code is correct.
> 
time_base_in and time_base_out always coincide, so adding the new
variable would be useless (and confusing). But if your "now" corresponds
to current master, then none of the variables are useless.

- Andreas