[FFmpeg-devel] [PATCH v2] avcodec/noise_bsf: add expr support

[Gyan Doshi]

On 2021-07-29 02:33, Michael Niedermayer wrote:
> On Wed, Jul 28, 2021 at 09:56:35AM +0530, Gyan Doshi wrote:
>> ---
>>   doc/bitstream_filters.texi |  64 ++++++++++++---
>>   libavcodec/noise_bsf.c     | 161 +++++++++++++++++++++++++++++++++----
>>   tests/fate/matroska.mak    |   2 +-
>>   3 files changed, 199 insertions(+), 28 deletions(-)
>>
>> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
>> index d10842ae47..46e4869f80 100644
>> --- a/doc/bitstream_filters.texi
>> +++ b/doc/bitstream_filters.texi
>> @@ -534,20 +534,62 @@ container. Can be used for fuzzing or testing error resilience/concealment.
>>   Parameters:
>>   @table @option
>>   @item amount
>> -A numeral string, whose value is related to how often output bytes will
>> -be modified. Therefore, values below or equal to 0 are forbidden, and
>> -the lower the more frequent bytes will be modified, with 1 meaning
>> -every byte is modified.
>> - at item dropamount
>> -A numeral string, whose value is related to how often packets will be dropped.
>> -Therefore, values below or equal to 0 are forbidden, and the lower the more
>> -frequent packets will be dropped, with 1 meaning every packet is dropped.
>> +Accepts an expression whose evaluation per-packet determines how often bytes in that
>> +packet will be modified. A value below 0 will result in a variable frequency.
>> +Default is 0 which results in no modification. However, if neither amount or drop is specified,
>> +amount will be set to @var{-1}. See below for accepted variables.
>> + at item drop, dropamount
>> +Accepts an expression evaluated per-packet whose value determines whether that packet is dropped.
>> +Evaluation to a positive value results in the packet being dropped. Evaluation to a negative
>> +value results in a variable chance of it being dropped, roughly inverse in proportion to the magnitude
>> +of the value. Default is 0 which results in no drops. See below for accepted variables.
>>   @end table
>>   
>> -The following example applies the modification to every byte but does not drop
>> -any packets.
>> +Both @code{amount} and @code{drop} accept expressions containing the following variables:
>> +
>> + at table @samp
>> + at item n
>> +The index of the packet, starting from zero.
>> + at item tb
>> +The timebase for packet timestamps.
>> + at item pts
>> +Packet presentation timestamp.
>> + at item dts
>> +Packet decoding timestamp.
>> + at item nopts
>> +Constant representing AV_NOPTS_VALUE.
>> + at item startpts
>> +First non-AV_NOPTS_VALUE PTS seen in the stream.
>> + at item startdts
>> +First non-AV_NOPTS_VALUE DTS seen in the stream.
>> + at item duration
>> + at itemx d
>> +Packet duration, in timebase units.
>> + at item pos
>> +Packet position in input; may be -1 when unknown or not set.
>> + at item size
>> +Packet size, in bytes.
>> + at item key
>> +Whether packet is marked as a keyframe.
>> + at item state
>> +A pseudo random integer, primarily derived from the content of packet payload.
>> + at end table
>> +
>> + at subsection Examples
>> +Apply modification to every byte but don't drop any packets.
>> + at example
>> +ffmpeg -i INPUT -c copy -bsf noise=1 output.mkv
>> + at end example
>> +
>> +Drop every video packet not marked as a keyframe after timestamp 30s but do not
>> +modify any of the remaining packets.
>> + at example
>> +ffmpeg -i INPUT -c copy -bsf:v noise=drop='gt(t\,30)*not(key)' output.mkv
>> + at end example
>> +
>> +Drop one second of audio every 10 seconds and add some random noise to the rest.
>>   @example
>> -ffmpeg -i INPUT -c copy -bsf noise[=1] output.mkv
>> +ffmpeg -i INPUT -c copy -bsf:a noise=amount=-1:drop='between(mod(t\,10)\,9\,10)' output.mkv
>>   @end example
>>   
>>   @section null
>> diff --git a/libavcodec/noise_bsf.c b/libavcodec/noise_bsf.c
> Thanks for implementing eval support

Will apply tonight if no further comments.

Thanks,
Gyan