FR: Support both distinct video format FourCCs in an AVI header

[LigH]

There are two distinct FourCCs in an AVI header describing the video stream:

1. the description of the video codec used to create the video stream (first appearance, just after the "vids" chunk ID);

2. the description of the video codec required to decode the video stream (second appearance in the "biCompression" field of the BITMAPINFOHEADER structure in the Stream Format chunk)

There are several cases of differences between them, e.g.:

• xvid / XVID
• divx / DX50 (to separate DivX 4 from DivX 5+)
• hfyu / FFDS (for the YV12 variant of Huffyuf, first supported in ffvfw)

Players should only be interested in the second (bitmap compression) FourCC, but you can't be sure that there are no players which would check both for supported values and refure playback if not both are as expected. Therefore I hope you can support forcing both FourCCs if desired, maybe in the format: -vtag divx:DX50

[cehoyos]

Please provide an example for which this feature would be needed.

[cehoyos]

Please reopen if you can explain a use-case for this feature-request.