[FFmpeg-devel] [PATCH]Reset rotation information when using the transpose filter

[Reimar Döffinger]

On 15 Nov 2012, at 19:57, Nicolas George <nicolas.george at normalesup.org> wrote:
> Le quintidi 25 brumaire, an CCXXI, Reimar Döffinger a écrit :
>> Well, I think there is rarely (never?) a use case for both.
>> So _ideally_ I would say the best thing would be to have these possible
>> behaviours:
>> 1) -vf rotate=n:hard : read in the metadata rotate from the input,
>> remove it on the output, rotate by n + previous metadata rotate
>> 2) -vf rotate=n:soft : do not do any processing, update or add
>> rotate metadata to correspond to the previous value + n.
> 
> Is there any good reason to keep soft rotation when transcoding? The way I
> see it, but I may be wrong, soft rotate is for rotating without transcoding,
> and hard rotate should be preferred whenever possible, if only because a lot
> of players will ignore soft rotate.

You might not care about those and want to save a bit of processing time.
You might also be able to get better compression/quality (both maximum size and motion vector length can differ for horizontal and vertical) and better decompression performance (basically, the less vertical movement the easier decoding is to parallelize).
It's rather theoretical though I guess.