Subject: [PATCH] examples/transcoding: Fix time_base handling

From: Jack Lau <[email-masked]>
Date: Tue, 4 Feb 2025 21:39:20 +0800

The `dec_ctx->time_base` was incorrectly default set to 0/60, while `enc_ctx->time_base` was derived from `dec_ctx->framerate`. This mismatch could cause incorrect video duration in the output.

This patch aligns `enc_ctx->time_base` with `dec_ctx->time_base` to prevent rescaling issues and ensure correct video duration.

Signed-off-by: JackLau1222 <[email-masked]>
---
 doc/examples/transcoding.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/examples/transcoding.c b/doc/examples/transcoding.c
index 013f89fc7d..847bdb7e1a 100644
--- a/doc/examples/transcoding.c
+++ b/doc/examples/transcoding.c
@@ -172,7 +172,7 @@ static int open_output_file(const char *filename)
                 else
                     enc_ctx->pix_fmt = dec_ctx->pix_fmt;
                 /* video time_base can be set to whatever is handy and supported by encoder */
-                enc_ctx->time_base = av_inv_q(dec_ctx->framerate);
+                enc_ctx->time_base = dec_ctx->time_base;
             } else {
                 enc_ctx->sample_rate = dec_ctx->sample_rate;
                 ret = av_channel_layout_copy(&enc_ctx->ch_layout, &dec_ctx->ch_layout);
@@ -180,7 +180,7 @@ static int open_output_file(const char *filename)
                     return ret;
                 /* take first format from list of supported formats */
                 enc_ctx->sample_fmt = encoder->sample_fmts[0];
-                enc_ctx->time_base = (AVRational){1, enc_ctx->sample_rate};
+                enc_ctx->time_base = dec_ctx->time_base;
             }
 
             if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
-- 
2.45.2