user6317: On the Internet, I sometimes see lower resolution videos that have a larger file size than a higher resolution version.
Which of these should have a better apparent quality when displayed on a 50'' FHD TV?
A 4GB 480p or a 2GB 1080p ???

user2836: There is no concrete answer to this. It depends entirely on the content of the video. Video compression effectively looks for patterns in video. If lots of patterns can be found, then high compression can be achieved with high resolution and low but rate.   If the video is hard to find patterns though, then high compression results in altering the video to make patterns and this produces artifacts that distort the video. 
Reducing the resolution of the file in these cases allows for fewer artifacts since less alterations need to be made to the video to find a pattern. 
I'm over simplifying here with some technical inaccuracies to make it more accessible, but that is the general idea for compression. If the hd video doesn't have artifacts then the hd video is better, but the sd file is far less likely to have artifacts if similar codecs were used for both. 

user3295: Well you CAN make rough assumptions. For a live action film a bit-rate of 3-8 Mbit/s is very advisable at 1080p. At 3Mbit/s you will very likely have noticable artifacts, thats usually an advisable bitrate for 720p video.
A file at SD resolution 480p/567p that is around 4GB in size you probably deal with a DVD that wasn't trans-coded for archiving.
Which is better is hard to say though, in case of a DVD encode you probably have MPEG2 or MPEG4-v2 encoded video and with HD/Blu-ray you will very likely have h264 which is more efficent than MPEG2/MPEG4-v2/Xvid (h264 is MPEG4-v10). So a low bitrate with h264 is not as bad as a low bitrate with MPEG2/MPEG4-v2/Xvid.
Generally I would probably go with the 1080p with less bitrate if its smaller in size, just because its smaller in size and its very likely that on a 1080p monitor/TV the video will not look worse than the upscaled DVD.

6317: <p>On the Internet, I sometimes see lower resolution videos that have a larger file size than a higher resolution version.</p>

<p>Which of these should have a better apparent quality when displayed on a 50'' FHD TV?
A 4GB 480p or a 2GB 1080p ???</p>
 2836: <p>There is no concrete answer to this. It depends entirely on the content of the video. Video compression effectively looks for patterns in video. If lots of patterns can be found, then high compression can be achieved with high resolution and low but rate.   If the video is hard to find patterns though, then high compression results in altering the video to make patterns and this produces artifacts that distort the video. </p>

<p>Reducing the resolution of the file in these cases allows for fewer artifacts since less alterations need to be made to the video to find a pattern. </p>

<p>I'm over simplifying here with some technical inaccuracies to make it more accessible, but that is the general idea for compression. If the hd video doesn't have artifacts then the hd video is better, but the sd file is far less likely to have artifacts if similar codecs were used for both. </p>
 3295: <p>Well you CAN make rough assumptions. For a live action film a bit-rate of 3-8 Mbit/s is very advisable at 1080p. At 3Mbit/s you will very likely have noticable artifacts, thats usually an advisable bitrate for 720p video.
A file at SD resolution 480p/567p that is around 4GB in size you probably deal with a DVD that wasn't trans-coded for archiving.</p>

<p>Which is better is hard to say though, in case of a DVD encode you probably have MPEG2 or MPEG4-v2 encoded video and with HD/Blu-ray you will very likely have h264 which is more efficent than MPEG2/MPEG4-v2/Xvid (h264 is MPEG4-v10). So a low bitrate with h264 is not as bad as a low bitrate with MPEG2/MPEG4-v2/Xvid.</p>

<p>Generally I would probably go with the 1080p with less bitrate if its smaller in size, just because its smaller in size and its very likely that on a 1080p monitor/TV the video will not look worse than the upscaled DVD.</p>
