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

[Don Moir]

> 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.

I look at the metadata rotate value as orientation for normal viewing. I have 3 files where it's set to 90, 180, and 270. If I don't 
take this into account, the video will be either sideways or upside down and this is not what the user expects. Additional rotation 
is independent of this.