[FFmpeg-user] dv => mp4: deinterlace or not, and how?

[sean darcy]

On 05/05/2011 06:32 PM, Mark Himsley wrote:
> On 05/05/2011 21:36, Baptiste Coudurier wrote:
>> Hi,
>>
>> On 05/05/2011 01:19 PM, sean darcy wrote:
>>> I have an interlaced dv file. I'm transcoding it with x264 to mp4.
>>>
>>> 1. ffmpeg -i file.dv -an -vcodec libx264 -b<x>  out.mp4
>>>
>>> If I just leave it like that, is out.mp4 interlaced or progressive?
>>
>> progressive. By default encoding is progressive.
>
> I'd like to clarify that answer.
>
> I agree 100% that the mp4 will be encoded progressive. The problem is
> that it could be badly encoding interlaced material. What I mean is, it
> will be using progressive frame encoding techniques to encode a frame
> that might be carrying interlaced material, which would therefore
> display with comb edges on movement etc.
>
> [...]
>>> 3. ffmpeg -i file.dv -an -vcodec libx264 -b<x>  -flags +ilme+ildct out.mp4
>>>
>>> Here I assume out.mp4 is interlaced. How is this different from 1.
>>> above? Is it different?
>>
>> Correct.
>
> It is different from 1 because it encodes the two fields as temporally
> different half-frames (if you don't mind my over-simplification).
>
> In your option 1, the encoder can reduce bit-rate by
> throwing-away/hiding stuff on every line of the picture, in one go.
> Because interlacing works by every other line being from a different
> temporal snapshot, that throwing-away/hiding could move pixels from one
> temporal snapshot to another. Than can look really horrible.
>
> In your opting 3 the encoder knows that the image is made up of the two
> temporal snapshots and will not do that, but can use its knowledge that
> the second snapshot may contain the same image as the first snapshot,
> only with some/all parts moved, to reduce the bit-rate - by encoding the
> second field as deltas from the first field.
>
Thanks. Very helpful. I have realized I need to deinterlace, but now I 
know what to do if I'm keeping the stream interlaced.