ffmpeg: copy trailing_padding when using -acodec copy

Signed-off-by: James Almer <jamrial@gmail.com>

ffmpeg.c

@@ -3000,6 +3000,7 @@ static int transcode_init(void)
                 enc_ctx->audio_service_type = dec_ctx->audio_service_type;
                 enc_ctx->block_align        = dec_ctx->block_align;
                 enc_ctx->initial_padding    = dec_ctx->delay;
+                enc_ctx->trailing_padding   = dec_ctx->trailing_padding;
                 enc_ctx->profile            = dec_ctx->profile;
 #if FF_API_AUDIOENC_DELAY
                 enc_ctx->delay              = dec_ctx->delay;