[FFmpeg-devel] [PATCH] avformat/avienc: fix fields-per-frame value for interlaced video streams

[Tobias Rapp]

On 22.11.2017 23:52, Carl Eugen Hoyos wrote:
> 2017-11-22 16:41 GMT+01:00 Tobias Rapp <t.rapp at noa-archive.com>:
>> Writes one set of field framing information for progressive streams and
>> two sets for interlaced streams. Fixes ticket #6383.
>>
>> Unfortunately the OpenDML v1.02 document is not very specific what value
>> to use for start_line when frame data is not coming from a capturing
>> device, so this is just using 0/1 depending on the field order as a
>> best-effort guess.
> 
> I believe your approach is sane but the only available examples
> may indicate that it should be set to something like height / 2 ;-(

Indeed my main problem is that I have not found some real-world example 
file with two sets of field framing information. I scanned the files at 
http://streams.videolan.org/samples/ but out of >900 AVI files only 
about 40 files contain a vprp chunk but none contains two fields.

I have found two files that have FieldPerFrame=2 (indicating an 
interlaced video stream) but they contain a truncated vprp chunk (no 
field framing information):
http://streams.videolan.org/samples/V-codecs/MJPEGs/matrox-capture.avi
http://streams.videolan.org/samples/avi/TRA3106.avi

As this clearly doesn't match the specs I didn't want to follow these 
two examples.

I can use height/2 for start_line offset instead of 1 if that sounds 
better, to me it would look like an indication that the fields are 
stored separated, but no strong opinion from my side.

Regards,
Tobias