user35344: I know it's possible with after effects, but is it possible to modify existing text in a mp4 file, without the original source file ?

user19692: With only an MP4 (movie container file often using H.264 codec), you cannot edit the text as text, only as an image. In the MP4 file, the text is now pixels (compressed, keyframed, digitized, whatever --  but still ultimately just image data, not text.)
MP4 files can have a subtitle stream, which could be separated from the image. But you mentioned text, so I assume you mean text overlaid within the image frame, not subtitle text.
One strategy would be to block or mask the existing text and replace it with new text superimposed over the image. I've had to do that to change captions on industrial videos.
You can also try to crop out the text, using only part of the frame and enlarging or letterboxing it to give you a new video without the text.

35344: <p>I know it's possible with after effects, but is it possible to modify existing text in a mp4 file, without the original source file ?</p>
 19692: <p>With only an MP4 (movie container file often using H.264 codec), you cannot edit the text as text, only as an image. In the MP4 file, the text is now pixels (compressed, keyframed, digitized, whatever --  but still ultimately just image data, not text.)</p>
<p>MP4 files can have a subtitle stream, which could be separated from the image. But you mentioned text, so I assume you mean text overlaid within the image frame, not subtitle text.</p>
<p>One strategy would be to block or mask the existing text and replace it with new text superimposed over the image. I've had to do that to change captions on industrial videos.</p>
<p>You can also try to crop out the text, using only part of the frame and enlarging or letterboxing it to give you a new video without the text.</p>
