[FFmpeg-devel] [PATCH v2 08/11] vaapi_encode_mjpeg: Warn if input is not full range

Mark Thompson sw at jkqxz.net
Sun Feb 10 20:21:42 EET 2019

On 05/02/2019 13:27, Carl Eugen Hoyos wrote:
> 2019-01-28 0:47 GMT+01:00, Mark Thompson <sw at jkqxz.net>:
>> +    if (avctx->color_range == AVCOL_RANGE_MPEG) {
>> +        av_log(avctx, AV_LOG_WARNING, "Input video does not appear "
>> +               "to use full-range: output colours may be incorrect.\n");
> The wording seems not ideal to me:
> Are you not sure if the encoder will produce correct output for
> mpeg-range jpeg?
> That's how it sounds to me...

The problem is that, unlike H.264 and other codecs, JPEG has no way to signal that the data are actually limited-range.  The encode will preserve the values, but those values will not have the right interpretation at a remote end which only looks at the JPEG data.  On the other hand, if signalled by some out-of-band method (perhaps the container, or you control both ends) everything is perfectly usable.

I agree the message isn't particularly clear; do you have any thoughts about how it should be phrased?

- Mark

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