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doc/examples/encode_video: add explanations in comments.

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This commit is contained in:
Nicolas George 2021-08-16 15:05:59 +02:00
parent 3969c2abfb
commit 1698cd8422
1 changed files with 21 additions and 3 deletions
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24
doc/examples/encode_video.c
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@ -155,12 +155,25 @@ int main(int argc, char **argv)
for (i = 0; i < 25; i++) { for (i = 0; i < 25; i++) {
fflush(stdout); fflush(stdout);
/* make sure the frame data is writable */ /* Make sure the frame data is writable.
On the first round, the frame is fresh from av_frame_get_buffer()
and therefore we know it is writable.
But on the next rounds, encode() will have called
avcodec_send_frame(), and the codec may have kept a reference to
the frame in its internal structures, that makes the frame
unwritable.
av_frame_make_writable() checks that and allocates a new buffer
for the frame only if necessary.
*/
ret = av_frame_make_writable(frame); ret = av_frame_make_writable(frame);
if (ret < 0) if (ret < 0)
exit(1); exit(1);
/* prepare a dummy image */ /* Prepare a dummy image.
In real code, this is where you would have your own logic for
filling the frame. FFmpeg does not care what you put in the
frame.
*/
/* Y */ /* Y */
for (y = 0; y < c->height; y++) { for (y = 0; y < c->height; y++) {
for (x = 0; x < c->width; x++) { for (x = 0; x < c->width; x++) {
@ -185,7 +198,12 @@ int main(int argc, char **argv)
/* flush the encoder */ /* flush the encoder */
encode(c, NULL, pkt, f); encode(c, NULL, pkt, f);
/* add sequence end code to have a real MPEG file */ /* Add sequence end code to have a real MPEG file.
It makes only sense because this tiny examples writes packets
directly. This is called "elementary stream" and only works for some
codecs. To create a valid file, you usually need to write packets
into a proper file format or protocol; see muxing.c.
*/
if (codec->id == AV_CODEC_ID_MPEG1VIDEO || codec->id == AV_CODEC_ID_MPEG2VIDEO) if (codec->id == AV_CODEC_ID_MPEG1VIDEO || codec->id == AV_CODEC_ID_MPEG2VIDEO)
fwrite(endcode, 1, sizeof(endcode), f); fwrite(endcode, 1, sizeof(endcode), f);
fclose(f); fclose(f);