[FFmpeg-user] Detect if an MTS file is interlaced or not?

[Mike Scheutzow]

Thomas Worth wrote:
> On Wed, Jun 8, 2011 at 2:13 AM, Thomas Worth <dev at rarevision.com> wrote:
>> I'd like to know if there's a way to tell if an MTS file is
>> interlaced, preferably without having to decode it first. The problem
>> I have is that libav always returns 59.94 for the frame rate of
>> interlaced NTSC streams, even though we know it's 29.97. And of
>> course, r_frame_rate always returns 0 with the "mpegts" format so I am
>> left to calculate the frame count manually. I need the correct frame
>> rate to do this, however and there's no way of telling ahead of time
>> whether the input video will be interlaced or not. Any ideas?
>>
> 
> Sorry to nag, but I didn't get a response to this. All I need is a way
> to determine whether an input MTS file (with an H.264 stream) is
> interlaced or not. I thought this could be accomplished by reading
> values from the MTS format context, but I've had no luck. I even tried
> decoding an AVFrame and reading the avframe->interlaced_frame value,
> but it did not report the frame as interlaced even though the video is
> indeed interlaced (comments in avcodec.h say this value is set by the
> decoder).
> 
> Obviously VLC is playing the file back at its intended frame rate even
> though the frame rate reported by avformat is 59.94 (the actual frame,
> not field rate should be 29.97). Where is it getting this information?
> It doesn't seem to be getting it from r_frame_rate, since that is
> always double the playback rate with MTS it seems.


It sounds as if you are trying to decode a file with video field 
pictures (as opposed to frame pictures.) The ffmpeg rate-estimation code 
always makes a mistake and doubles the frame rate in this situation.

I use '-r 30000/1001' on the command line to just tell ffmpeg the 
correct frame rate.

 > It doesn't seem to be getting it from r_frame_rate, since that is
 > always double the playback rate with MTS it seems.

The double rate is not an artifact of the container. The container knows 
nothing about the frame rate.


Mike Scheutzow